Scrap Tires: Handbook on

Recycling Applications

and Management for the

U.S. and Mexico

December 2010

Office of Resource Conservation and Recovery

1200 Pennsylvania Avenue NW 

Mail Code: 5304P 

Washington DC 20460

www.epa.gov/waste

EPA530-R-10-010
DISCLAIMER

This document has undergone USEPA and external review by subject matter experts. All web links provided 

in this document were accurate and valid at the time of publication. Mention of trade names or commercial 

products does not constitute endorsement or recommendation for use.

Several web links provided in this document are not contained in domains created or maintained by USEPA. 

These links simply provide access to additional information in accordance with the intended purpose of this 

document. The USEPA cannot attest to the accuracy of information or the privacy protection provided by any 

external web site. Providing links to external web sites does not constitute an endorsement by USEPA of the 

site sponsors or the information or products presented on the sites.
i

Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

TABLE OF CONTENTS

Acknowledgements........................................................................................................................................ ii

Acronyms........................................................................................................................................................ iii

Chapter 1: Introduction ................................................................................................................................. 1

Background on U.S. - Mexico Border Region............................................................................................................................................1

Overview................................................................................................................................................................................................................2

Chapter 2 Scrap Tire Management Program Characteristics ...................................................................... 3

U.S. State Involvement......................................................................................................................................................................................3

Abatement Planning .........................................................................................................................................................................................7

Contractors........................................................................................................................................................................................................ 14

Project Management...................................................................................................................................................................................... 16

Summary ............................................................................................................................................................................................................ 20

Chapter 3 Ground Rubber............................................................................................................................21

Major U.S. Ground Rubber Markets........................................................................................................................................................... 21

Athletic and Recreational Surfaces Market............................................................................................................................................ 22

Molded and Extruded Products................................................................................................................................................................. 27

Rubber Modified Asphalt.............................................................................................................................................................................. 30

Other Markets................................................................................................................................................................................................... 32

Summary ............................................................................................................................................................................................................ 33

References.......................................................................................................................................................................................................... 33

Chapter 4 Energy Utilization .......................................................................................................................35

Chemical Characteristics of Scrap Tires................................................................................................................................................... 35

Cement Kilns..................................................................................................................................................................................................... 38

Combined Energy/Materials Recovery: Pyrolysis/Gasification ....................................................................................................... 47

Summary ............................................................................................................................................................................................................ 50

References.......................................................................................................................................................................................................... 50

Chapter 5 Tire Derived Aggregate and Whole Tires for Civil Engineering Applications.........................51

TDA as Drainage Aggregate ........................................................................................................................................................................ 52

TDA as Lightweight Fill.................................................................................................................................................................................. 58

Whole Tires for Wall Construction.............................................................................................................................................................. 66

References.......................................................................................................................................................................................................... 67

Chapter 6 Transportation and Processing Economics ...............................................................................71

Collection and Transportation.................................................................................................................................................................... 71

Processing .......................................................................................................................................................................................................... 73

Economic Sensitivity ...................................................................................................................................................................................... 79

Summary ............................................................................................................................................................................................................ 80

Chapter 7 Conclusion ...................................................................................................................................81

Glossary.........................................................................................................................................................83

Appendix A TDA Material Specifications.................................................................................................. A-1

Appendix B Design Guidelines To Minimize Internal Heating of Tire Shred Fills .................................. A-3

Appendix C Engineering Properties of TDA............................................................................................. A-5

Appendix D Calculation of Final In-Place Unit Weight and Overbuild................................................. A-11

Appendix E Case Histories – Use of TDA as Lightweight Embankment Fill.......................................... A-15

Appendix F Comparative Transportation Cost Example ....................................................................... A-21

Appendix G Scrap Tire Processing Facility Economic Parameters ........................................................ A-23

Appendix H Comparative Volume Sensitivity Of Tire Processing Facilities......................................... A-27
ii

Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

ACKNOWLEDGEMENTS

Through the U.S.- Mexico Border 2012 program, USEPA designed this handbook in cooperation with SEMARNAT 

as a resource for developing scrap tire markets in the border region between Mexico and the United States—

although the information is useful for any country. 

USEPA would like to specifically thank Mr. Terry Gray of T.A.G Resource Recovery and Dr. Dana Humphrey of the 

University of Maine as primary authors of this document. They are highly respected experts in the scrap tire 

field. Neither Mr. Gray nor Dr. Humphrey are USEPA employees.

The following individuals also made significant contributions to the document: 

Jose Arreola, Border Environment Cooperation Commission (BECC)

Michael Blumenthal, Rubber Manufacturers Association

Jack Brunner, Tetra Tech EM Inc.

Bethany Hand, Tetra Tech EM Inc. 

Ellie Kanipe, USEPA Office of Resource Conservation and Recovery, Border 2012 Program

Todd Marvel, Illinois EPA

Christopher Newman, USEPA Region 5

Adriana Oropeza, SEMARNAT

Rick Picardi, USEPA Office of Resource Conservation and Recovery, Mexico/Commission for Environmental 

Cooperation Team 

Emily Pimental, USEPA Region 9, U.S. – Mexico Waste Management Program

Paul Ruesch, USEPA Region 5 

Julie Shannon, USEPA Pollution Prevention Division

Mary Sikora, Tire Industry Association
iii

Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

o

C Degree Celsius

o

F Degree Fahrenheit 

ρ Density 

% Percentage

AASHTO American Association of State 

Highway Transportation Officials 

Al2

O3 Aluminum oxide

ARA American Retreaders’ Association

ASTM American Society for Testing and 

Materials

Btu British thermal units 

c Coefficient

CaCO3 Calcium carbonate

CalRecycle California Department of Resources 

Recycling and Recovery

CaO Calcium oxide

CCL Compacted clay liner 

CFR Code of Federal Regulations

cm Centimeter

cm/s Centimeters per second 

CM Columbus McKinnon

CO Carbon monoxide

CO2 Carbon dioxide

CRREL Cold Regions Research and 

Engineering Laboratory

CRMAC Crumb rubber modified asphalt 

concrete

EPDM Ethylene-propylene-diene monomer 

EQUIV Equivalent

ESPs Electrostatic precipitators 

F&B F&B Enterprises

Fe2

O3 Iron oxide

FIFA Fédération Internationale de Football 

Association 

g/m2

 Grams per square meter 

GIS Geographic Information System 

GPS Global Positioning System

H2

O Water

HCl Hydrochloric acid

ISC Industrial Source Complex

ISTEA Intermodal Surface Transportation 

Efficiency Act, 1990

K Earth pressure coefficient 

K2

O Potassium oxide

Ko Coefficient of lateral earth 

pressure at rest

kh Semi-empirical value

kcal/kg Kilocalories per kilogram 

kg Kilogram

km Kilometer

kPa KiloPascals

kW KiloWatt

kW/yr KiloWatt per year

lbs Pounds

lbs/hour Pounds per hour

LCRS Leachate Collection and Removal 

System 

LFG Landfill gas 

m Meter

m2 Square meter 

m3

/sec Cubic meter per second

Mg/m3

 Macrograms per cubic meter

MgO Magnesium oxide

mm Millimeter

ACRONYMS
iv

Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

MSW Municipal Solid Waste

MSWLF Municipal Solid Waste Landfills 

mw/yr MegaWatt/year

NA Not available

Na2

O Sodium oxide

NAPA U.S. National Asphalt Paving 

Association

NCAA National Collegiate Athletic 

Association 

ND Not detected

NOx Nitrogen oxide

NTDRA U.S. National Tire Dealers and 

Retreaders Association

OTR Off the Road 

oz/yd3 Ounces per cubic yard 

OGFC Open-graded friction course

P2

O5 Phosphorus pentaoxide

PAH Polynuclear aromatic hydrocarbons 

PCBs Polychlorinated biphenyls

PCDD olychlorinated dibenzodioxins 

(dioxins)

PCDF Polychlorinated dibenzofurans

pcf Pounds per cubic foot

PNA Polynuclear aromatics

psf Pounds per square foot 

psi Pounds per square inch 

PTE Passenger tire equivalent 

PVC Polyvinyl chloride

Q Surcharge

RCRA Resource Conservation Recovery Act

Ref Reference

RFP Request for Proposals

RFQ Request for Qualifications 

RMA U.S. Rubber Manufacturers Association 

RPA U.S. Rubber Pavements Association

RUMAC Rubber Modified Asphalt Concrete

SBR Styrene-butadiene rubber 

SEMARNAT Secretaría de Medio Ambiente 

y Recursos Naturales (Mexican 

Ministry of Environment and Natural 

Resources)

SiO2 Silicon dioxide

SOx Sulfur oxide

SO3 Sulfur trioxide

STMC U.S. Scrap Tire Management Council

TDA Tire-derived Aggregate

TDF Tire-derived fuel

TiO2 Titanium dioxide

TISC Tire Industry Safety Council

TOX Toxicity

TRA Tire Removal Agreement

TRIB U.S. Tire Retread Information Bureau 

TRRMMG U.S. Tread Rubber and Repair Materials 

Manufacturers Group (formerly the 

Tread Rubber Manufacturers Group)

US United States

USDOT U.S. Department of Transportation

USEPA U.S. Environmental Protection Agency

UV Ultraviolet

WSW White sidewall tires

YCCL Yolo County Central Landfill
1

Chapter 1: Introduction Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

BACKGROUND ON U.S. – MEXICO 

BORDER REGION

Scrap tires pose a problem in both the United States 

and Mexico. In the United States alone, 275 million 

tires were in stockpiles in 2003, and approximately 

290 million new scrap tires were generated, according 

to the U.S. Rubber Manufacturers Association. In 

Mexico, the Mexican Ministry of Environment and 

Natural Resources (SEMARNAT) estimates that about 

40 million scrap tires are generated annually. Millions 

of these scrap tires are stockpiled throughout the U.S.-

Mexico Border region, threatening the environmental 

and public health of both the U.S. and Mexico. 

These piles pose a public health concern. They are 

breeding grounds and havens for mosquitoes and 

other vectors, resulting in the spread of dengue 

fever, yellow fever, encephalitis, West Nile virus, and 

malaria. Improperly managed in stockpiles, in illegal 

dumps, and scattered along road sides, scrap tires 

are a significant border environmental problem as 

a result of the leaching process, fires hazards, and 

water contamination. Once ignited, tire fires are 

difficult to extinguish. When water is applied to fight 

the fire, serious air, ground water, and surface water 

contamination may result. Toxic emissions from tire 

fires, such as sulfuric acid and gaseous nitric acid, can 

irritate the skin, eyes, and mucus membranes, and can 

affect the central nervous system, cause depression, 

have negative respiratory effects and, in extreme 

cases, cause mutations and cancer. 

The scrap tire problem is heightened in the 

U.S – Mexico border region. There are 46 

known tire piles in the U.S.–Mexico border 

region, according to the Border 2012: 

U.S.-Mexico Border Scrap Tire Inventory 

Summary Report (May 2007). This border 

region is defined by the 100-kilometer 

(km) area on each side of the more than 

3,200–km-long (2,000 miles) border 

between the two countries. Throughout 

the entire border region, scrap tires are 

stockpiled at municipal solid waste landfills; 

junkyards; small businesses; and other 

privately or publicly owned properties. 

In 2008, the largest tire pile was located 

near Ciudad Juárez and it contained more 

than 4 million tires. Similarly, during the 

early stages of scrap tire management in the U.S., it 

was estimated that over 1 billion tires were in scrap 

tire piles throughout the United States. Further 

discussion on the tire problem can be found in the 

Good Neighbor 12th Report at www.epa.gov/ocem/

gneb/gneb12threport/English-GNEB-12th-Report.pdf.

The scrap tire problem is fueled by the current 

economic variations within the U.S.-Mexico border 

region. Millions of used tires move from the United 

States to northern Mexican border states for 

reuse and disposal. Because of their lower cost, 

approximately half of all tire purchases in Mexican 

border cities are used tires from the United States. 

They have a shorter lifespan than new tires 

because they are used tires with generally 15,000 

to 30,000 km (10,000 to 20,000 miles) of wear. 

Mexican law permits 1 million used tires to be 

imported across the border each year, which are 

reserved for the ports of entry in the states of Baja 

California (Tijuana and Mexicali) and Chihuahua 

(Ciudad Juárez). The Mexican State of Sonora 

also has a policy on used tire import. However, 

it is likely that more scrap tires may enter Mexico 

without proper authorization each year. For these 

reasons, the tire problem in the border region is 

significant. 

Scrap tires are processed differently in the United 

States and Mexico. In many U.S. states, scrap tires 

are regulated as a municipal solid waste under 

the U.S. Resource Conservation and Recovery Act 

CHAPTER 1

Introduction

Exhibit 1-1 United States – Mexico border region
2

Chapter 1: Introduction Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

(RCRA). Regulations are enforced at the state level, 

and most states have enacted scrap tire legislation. 

Common features of U.S. scrap tire programs include 

the following: 

•	 Taxes on tires or automobiles for program

funding

•	 Licensing or registration requirements for scrap

tire transporters, storage, processors, and some 

end users

•	 Manifests for scrap tire shipments

•	 Limitations on who may handle scrap tires

•	 Financial assurance requirements for scrap tire

handlers

•	 Market development. 

Through these efforts, the United States has 

increased the number of scrap tires sent to enduse markets from 17 percent in 1990 to more 

than 89 percent in 2007, according to the U.S. 

Rubber Manufacturers Association. As of 2007, 

the majority of tires in the United States were 

processed as tire derived fuel (TDF) (54 percent), 

in addition to civil engineering and ground rubber 

applications such as landfill drainage, rubberized 

asphalt, filtering septic systems, and other 

markets. 

In Mexico, scrap tires are governed under the 

2004 “General Law for the Prevention and Integral 

Management of Waste.” Under this law, every 

major generator of waste, including municipalities 

and industrial facilities, are required to develop 

integrated waste management plans. Scrap 

tires are “special management waste” under this 

law and, therefore, require an integrated waste 

management plan. 

Through the U.S.-Mexico Border 2012 Program 

(Border 2012), SEMARNAT and the U.S. 

Environmental Protection Agency (USEPA) are 

working jointly to clean up the border’s scrap tire 

piles and to find efficient and environmentally sound 

options for using them. Originating from the 1983 

La Paz Agreement, Border 2012 is a results-driven 

partnership among U.S. and Mexican federal, state, 

local governments, and U.S. tribes to protect public 

health and improve environmental conditions along 

the U.S.–Mexico border. Through Border 2012, 

SEMARNAT and USEPA promote partnerships with 

industry, academia, and all levels of government as 

they clean up tire piles (more than 5 million scrap 

tires were cleaned up from 2003 to 2009) and take 

steps to prevent further tire piles. These steps include 

developing this handbook; a border-wide inventory of 

tire piles; a compendium of border scrap tire projects; 

and an ongoing multi-stakeholder group that meets 

annually to collaborate in finding solutions. These 

plus additional resources and publications can 

be found on the Border 2012 Waste Policy Forum 

website, at www.epa.gov/usmexicoborder/fora/wasteforum/index.html.

OVERVIEW

The Scrap Tires: Handbook on Recycling Applications 

and Management for the U.S. and Mexico provides 

a resource for federal, state, and local governments 

along with private industry in developing markets 

for the valuable resources contained in scrap tires. 

Specific markets and applications addressed include 

energy use, tire-derived aggregate, and ground 

rubber. Transportation and processing economics 

are also discussed. This handbook is intended to 

accelerate scrap tire market development efforts 

by providing critical information based on past 

experiences. Technical, environmental, economic, 

and reference information is provided for major 

scrap tire recycling applications to allow industry 

and government to assess, prioritize, target, and 

develop markets as efficiently and rapidly as possible. 

Finally, the handbook presents information and 

lessons learned from those who have established 

and effectively managed scrap tire management 

programs. With this information, the handbook 

should further efforts in preventing creation of 

additional scrap tire piles, thereby helping to clean 

up border communities. This handbook has been 

developed specifically for the U.S.-Mexico border 

although the information is useful for any country. 

Whole tire erosion control wall, Los Arroyos, Mexico
3

Chapter 2: Scrap Tire Management Program Characteristics Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

CHAPTER 2

Scrap Tire Management 

Program Characteristics

This chapter provides information, based on 

the experiences of U.S. states, on setting up and 

implementing a regulatory tire management 

program. It is important to note that, although 

both the U.S. and Mexico have federal systems 

of government, historically Mexico has a more 

centralized, coordinated federal government, whereas 

powers tend to be distributed and passed down to 

state and local levels of government in the United 

States. In the U.S., although waste management is 

federally mandated, each state has the authority to 

establish the path it will follow to achieve compliance 

and the responsibility to manage the program. This 

information is based on USEPA’s Scrap Tire Cleanup 

Guidebook: A Resource for Solid Waste Managers 

across the United States. Additional information on 

U.S. EPA state scrap tire programs can be found on 

USEPA’s website at www.epa.gov/epawaste/conserve/

materials/tires/live.htm. The sections in this chapter 

explain various aspects involved in creating and 

managing a scrap tire program, based on lessons 

learned and case studies from a number of states. 

These sections are:

•	 U.S. State Involvement: Describes alternative 

approaches that states have used to develop and 

fund scrap tire programs.

•	 Abatement Planning: Provides information 

on how states identify and map stockpiles, their 

quantity estimation techniques, and approaches 

to setting priorities among stockpiles.

•	 Contractors: Describes how states evaluate 

the qualifications of potential contractors (also 

called consultants), their bidding and award 

processes, the types of contracts states use, 

and issues regarding bonding and insurance 

and capacity assessment.

•	 Project Management: Based on experiences 

in the United States, this section discusses 

considerations for improving management 

and implementation of tire stockpile 

abatement or cleanup projects. 

U.S. STATE INVOLVEMENT

In the United States, states are the driving force 

behind control and abatement of scrap tire 

stockpiles. Broad state adoption of regulations 

and regional coordination of neighboring 

states and local governments have dramatically 

decreased the incidence of illegal scrap tire 

storage and disposal. However, local regulations 

have a limited impact on controlling statewide 

scrap tire movement and accumulation. Scrap 

tires can be transported short distances 

inexpensively, so they usually are moved to the 

nearest unregulated jurisdiction or the destination 

with the lowest disposal cost. Concerns over the 

costs and hazards associated with large stockpiles 

as well as the proliferation of new stockpiles have 

driven most legislation in the United States. 

Factors Influencing a Scrap Tire Abatement Program

•	 Quantity: The number of stockpiles and the total scrap tire quantity affect the abatement schedule.

•	 Resources: Financial and staff resources required to plan, contract for, and monitor multiple site 

abatement projects must be available.

•	 Access: Obtaining site access for abatement can be a prolonged legal process, depending on the 

procedures defined in the enabling legislation.

•	 Infrastructure: Capacity limitations of both contractors and markets must be recognized to avoid 

detrimental impacts on the use of scrap tires being generated. The overall objective should be to 

create a sustainable infrastructure for using scrap tire resources over the long term.
4

Chapter 2: Scrap Tire Management Program Characteristics Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

This section defines important regulatory and 

enforcement roles that U.S. states have assumed 

to control and abate scrap tire stockpiles. Many 

stockpiles were created decades ago, when storage 

was unregulated. As a result, many states are forced 

to fund cleanup of these “legacy” stockpiles because 

those involved in creating the stockpiles lack the 

resources necessary to clean them up. Furthermore, 

no single scrap tire program is universally applicable 

because states have different industrial, economic, 

political, and geographic characteristics. Therefore, 

this section discusses alternatives that states have 

successfully used in developing and funding 

programs. 

 Scrap Tire Cleanup Programs and 

Funding

Scrap tire stockpiles do not have a positive net 

value because abating stockpiles costs more than 

can be derived from revenue generated from 

scrap tire uses. If stockpile owners are unable 

or unwilling to fund cleanups, the stockpiles 

become public liabilities, and funding to abate 

the associated public health and environmental 

hazards must be provided.

States in the U.S. generally establish funding 

mechanisms within the legislation that initiates 

the scrap tire programs. In general, most 

programs begin by documenting the extent of the 

problem by identifying, quantifying, and setting 

priorities among stockpiles. Furthermore, the 

presence of a processing and market infrastructure 

is important because most abatement programs 

seek to use scrap tires removed from stockpiles. 

 Effective scrap tire programs generally have the 

following financial management characteristics:

Dedicated Funding Source

Effective scrap tire programs require consistent 

and continuing funding. Ongoing monitoring and 

enforcement programs are required to prevent 

new stockpiles after existing stockpiles have been 

remediated. Dedicated trust funds have been used 

successfully to achieve uniformity, but the trust fund 

money may be re-allocated to non-tire program 

priorities during state budget shortfalls. More 

information on fee programs and funding can be 

found on line at www.epa.gov/epawaste/conserve/

materials/tires/laws.htm. 

Using a Dedicated Trust Fund for 

Scrap Tire Abatement in Oregon

Oregon initiated its waste tire management 

program in 1988, depositing the net revenue 

from its $1.00 per tire fee (minus $0.15 per tire for 

the dealer and $0.035 per tire in administrative 

costs) in a dedicated trust fund. Between 1988 

and 1993, Oregon abated 3,823,440 tires at 

63 sites at a cost of $3,749,041 and undertook 

101 other voluntary cleanups. The fund also 

supported market development and established 

an ongoing regulatory framework for processors 

and haulers. When the program ended in 1993, 

about $1.4 million remained in the trust fund. 

Enforcement efforts are now supported under 

the general umbrella of solid waste management 

fees levied on landfills.

Scrap Tire Abatement and 

the California Tire Recycling 

Management Fund 

In conjunction with the California Tire Recycling 

Act of 1989, the state established the Tire 

Recycling Management Fund. Funds are 

collected through the California Department of 

Resources Recycling and Recovery (CalRecycle), 

previously the California Integrated Waste 

Management Board, program that charges $1.75 

per tire on the sale of new motorized vehicle, 

construction equipment, or farm equipment 

tires. Revenues generated from the program 

are used for waste tire management such as 

research on new recycled tire use, assistance 

to local scrap tire program management, 

regulation of scrap tire facilities and tire haulers 

to protect public health and the environment, 

public education programs, storage of tires, and 

business development. Through this program, 

California estimates that approximately 75 

percent of scrap tires generated in 2004 were 

used in some way. Since the program began, 

California has been able to use some of the funds 

generated to support several scrap tire grants, 

including tire cleanup and amnesty, rubberized 

asphalt programs, tire-derived aggregate, 

business assistance, and tire enforcement. 

These grants have been invaluable in ensuring 

the sustainability of scrap tire programs in the 

state. Additional information on California Tire 

Management can be found on line at www.

calrecycle.ca.gov/Tires.
5

Chapter 2: Scrap Tire Management Program Characteristics Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

Adequate Resources

In general, funding levels equivalent to at least $1 

per scrap tire have proven adequate to implement 

comprehensive programs, with 35 to 50 percent of 

the funds initially committed to stockpile abatement. 

Market development grants are often available to 

assist in launching these programs. Providing grant 

funding would be a viable option for programs 

seeking support in Mexico. 

Funding Flexibility and Accrual

Abatement funds are often accrued in the early stages 

of the program while scrap tire stockpiles are being 

identified, prioritized, and legally accessed. This 

funding allows subsequent contractual commitments 

to be met and provides contingency funds for 

unpredictable events. As abatement is completed, 

it is generally appropriate to shift funding to other 

program priorities or to reduce revenue.

Regulatory and Permitting Programs

States have found that regulations and infrastructure 

are necessary for an abatement program to be 

effective and efficient. If management, transport, 

and disposal of the scrap tires generated each day 

are not controlled by regulations, new stockpiles will 

be created as old ones are cleaned up. Although 

some states have been successful with limited 

permitting or no permitting at all, others monitor tire 

movement with comprehensive manifest systems 

and require permits for all businesses involved. 

There have been successes and failures in both 

approaches. The primary objective of a regulatory 

or permitting program is generally to ensure the 

proper transportation, storage, recycling, and disposal 

of scrap tires and to prevent formation of illegal 

stockpiles. 

Processing and Storage Facilities

Some of the largest scrap tire stockpiles have been 

created at processing facilities or at storage facilities 

formed in anticipation of future processing, often 

before state programs were implemented. Virtually 

all state programs regulate processing and storage 

locations to control scrap tire accumulation. 

Storage facilities are generally required to be 

permitted or registered to store any scrap tire in 

quantities above a stated minimum that can typically 

range from 50 to 10,000 tires. The minimum should 

be carefully considered. Experience has shown the 

optimum quantity to be 1,500 to 2,500 tires, which 

allows a new tire store to accumulate a truckload of 

tires for optimum hauling efficiency.

Processing and larger storage facilities are 

generally permitted or registered. Maximum 

storage limits are normally established during 

permitting. Low limits can impair efficient 

operations by preventing maintenance of 

adequate inventories to compensate for inherent 

variations in supply, equipment maintenance 

downtime, or market fluctuations. On the other 

hand, high limits can increase public liability.

Haulers

Haulers, or transporters, may be considered the 

weak link in the scrap tire management chain. The 

transportation part of the scrap tire business is 

extremely competitive, and ultimately the disposal 

fee represents a major percentage of the revenue 

that haulers collect from new tire dealers. Controls 

are often necessary to reduce the possibility that 

haulers will use inappropriate disposal measures. 

One option states employ is to register haulers 

annually and provide decals, medallions, or placards 

for display at a prescribed location on each transport 

vehicle. This option allows enforcement officials to 

check compliance from their vehicles. Some states 

require financial assurance for each scrap tire-related 

vehicle or business, with varying amounts up to 

$20,000 per business. Small haulers are generally 

exempt from this measure; however, this group is 

most likely to illegally dump tires. Most states either 

do not require hauler bonds or keep them relatively 

small on a per-vehicle or per-business basis. 

Florida Enforcement Efforts Target 

Haulers and Tire Store Owners

As part of its efforts to control illegal dumping 

and formation of scrap tire stockpiles, Florida 

has developed regulations that require scrap tire 

haulers to register with the state and tire stores 

to use only registered haulers. Enforcement 

officers in one county conducted a “sting” 

operation when undercover officers posing 

as unregistered haulers offered to take scrap 

tires at below-market cost from tire stores. 

At the conclusion of the operation, 24 store 

managers who accepted the offer were served 

with warrants from the state attorney’s office 

for a statutory violation punishable by a fine of 

up to $1,500 and 1 year in jail. The judge was 

generally lenient with the managers as firsttime offenders. The sting served as a warning 

to store owners and focused broad public 

attention on proper tire disposal practices. 
6

Chapter 2: Scrap Tire Management Program Characteristics Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

Tire Stores

Tire stores can play a key role in preventing illegal 

disposal of scrap tires. When a store owner or 

operator receives a quote for tire disposal that is 

below the market price, it likely involves illegal 

disposal. An auditable trail is maintained, however, 

if the owner or operator is required to keep records 

of the registered hauler decal numbers and the tire 

quantities handled. A state with a manifest system 

can reinforce the responsibility of stores by requiring 

them to maintain a copy of each completed manifest 

showing the ultimate disposal site, as has been done 

in Oklahoma and Texas. Other states require hauling 

and disposal receipts to be maintained on the store’s 

property; however, the receipts are not required to 

be submitted to the regulatory agency. This system 

still allows for the regulatory agency to audit a used 

tire store’s records without the administrative costs 

of a formal manifest system.

Enforcement and Cost Recovery 

Tactics

Enforcement and abatement cost recovery tactics 

are integrally linked. With a goal of facilitating 

site access and scrap tire stockpile removal, it is 

important to avoid creating legal and economic 

obstacles that may delay abatement. Several 

states allow their agencies to enter into stockpile 

access and abatement agreements at public 

expense without cost recovery. This approach 

expedites site cleanup, and the site owner or operator 

usually welcomes the assistance. However, the 

approach increases public expense and provides no 

incentive to mitigate sites. This leniency may also lead 

to additional stockpile formation, as the site owner 

may simply open another site nearby.

Other states — Illinois, Nebraska, New York, and Ohio, 

for example — have provisions that allow agencies 

site access to conduct stockpile abatement without 

forfeiting cost recovery. 

Dedicated Legal Assistance 

Obtaining support from legal experts within 

a regulatory agency can be a major obstacle. 

Dedicating legal staff in both the regulatory agency 

and attorney general’s office can help to achieve 

successful legal efforts. 

Initial Legal Support

Rigorously supporting the initial legal proceedings 

(complaints, testimony, and depositions) with sound 

preparation, good research, and expert testimony 

can encourage defendants to take action and send a 

signal to others in the scrap tire industry.

Negotiations

When cases are strong and the regulatory department 

is determined, some site owners recognize the 

economic advantage of mitigating sites on their 

own. They can typically mobilize contractors and 

Illinois Use of Tire Removal 

Agreements

One option for avoiding obstacles to 

enforcement and cost recovery is use of 

a voluntary tire removal agreement (TRA) 

between the owner of a property where scrap 

tires are located and the regulatory agency or 

department. This voluntary, written agreement 

allows removal of all scrap tires from the 

property at no cost to the state. Provisions must 

be established in the TRA to ensure that the 

tire pile is cleaned up in a manner that is fully 

protective of human health and the environment 

during the entire period of the agreement. 

Statutory authority may allow for maximum 

removal schedules, such as 3 months if the site 

holds 1,000 or fewer tires or 1 year if the site 

holds more than 10,000 tires. Extensions of the 

removal schedule may be allowed if the property 

owner is operating in good faith to execute the 

agreement.

Forced Cleanups in Illinois

State of Illinois Compiled Statute 415, Title XIV, 

governs all used tire management practices; 

Section 55.3d of this statute enables the Illinois 

EPA to notify a landowner of the environmental 

and public health hazards associated with 

a scrap tire stockpile. The landowner then 

has an opportunity to develop, submit to the 

Illinois EPA, and implement an abatement 

plan. If the landowner is unwilling or unable to 

comply with the removal schedule, or does not 

submit a removal schedule in response to the 

notification, the state is granted access to the 

property via existing statutory authority. As an 

added precaution to confirm protection of the 

landowner’s constitutional rights, the Illinois EPA 

uses an access agreement that is signed by the 

landowner before the cleanup. If the landowner 

refuses to sign the access agreement, the Illinois 

EPA will then go into court to seek site access 

from a judge. Illinois EPA’s access agreement 

is available at www.epa.gov/reg5rcra/wptdiv/

solidwaste/tires/guidance/index.htm.
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select disposal methods at a lower cost than the 

department. Additionally, they can avoid the legal 

costs and state administrative expenses that would be 

incurred in legal cases. 

Judgment Collections

Only a small percentage of legal actions, or 

judgments, taken against site owners and operators 

are successfully realized. Offenders can hide assets, 

declare bankruptcy, or disappear. The primary 

value of cost recovery is to create an incentive for 

landowner abatement of a site, and not to realize 

financial judgments against offenders without assets.

Liens

Liens can be the most effective method of cost 

recovery from site owners. Most states do not 

foreclose on liens but hope to gain some revenue 

from negotiated interim payments or from sale of 

the property (especially commercial property) in the 

future.

ABATEMENT PLANNING

Scrap tire stockpile abatement is a technical, 

economic, and political challenge. Cleanups involve 

elusive factors such as weather, stockpile contents, 

and underlying topography. This section presents 

critical planning considerations states have used 

for both overall cleanup programs and individual 

abatement projects.

Stockpile Identification and Mapping

Stockpile identification is the first step in defining 

the magnitude of the scrap tire stockpile problem in 

any jurisdiction. The most effective methods have 

involved all levels of government and enforcement as 

well as industry groups and citizen reports.

State Government

State solid waste and public health departments play 

a focal role in scrap tire stockpile identification efforts 

and have a broad range of organizational structures. 

Centralized departments deploy personnel to each 

region of the state to work with county, city, and 

local officials in identifying and characterizing sites. 

Other departments either designate one person 

in each region to identify stockpiles or distribute 

responsibility to all staff based on geographic or 

industry area of expertise. Smaller identification 

groups are easier to train and gain greater knowledge 

through in-depth experience. However, these 

advantages can be offset by greater travel time, cost, 

and difficulty in making regular visits to examine 

changing site conditions.

One effective compromise is to use a broad base of 

personnel to identify stockpiles in their service areas 

and then task a smaller group to characterize and 

prioritize stockpiles. Contractors or consultants may 

be useful for supplementing agency resources in the 

early stages of program implementation. 

County and Local Governments

Most effective programs have drawn on county, city, 

and local governments to identify stockpiles. Police, 

code enforcement, mosquito control, solid waste 

management, public health, park, firefighting, 

and forestry personnel have all helped to identify 

stockpiles they encountered during their routine 

activities. 

One U.S. state sent surveys to all county and local 

governments that asked for stockpile sites to be 

identified by location, street address, and owner. 

Cooperation in these efforts can be enhanced 

by the survey objectives and methodology and 

by explaining the program’s ability to help local 

governments abate sites without using local 

resources.

Additional Identification Methods

Other creative methods can be used to support 

identification efforts, including the following 

approaches:

•	 A toll-free telephone number can be

established to encourage residents to report 

stockpiles and illegal disposal. 

•	 Both public service announcements and

promotion of initial abatement activities 

encourage reporting of additional stockpiles.

•	 Representatives of tire dealers, salvage

yards, and haulers can reach out within 

their industries to encourage stockpile 

identification.

Required Information

Once a stockpile is identified, characterization 

is conducted to gather information required for 

prioritization, stabilization, and abatement. The 

following information is particularly useful, especially 

for larger sites:

•	 Location, including street address, city, county,

and global positioning system (GPS) coordinates.

•	 Owner or operator’s name, address, telephone

number, and involvement.

•	 Stockpile characteristics such as dimensions, tire

sizes, age, tire compaction, whether scrap tires 
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are stacked or laced, the percentage of whole tires 

and shreds, and the presence of rims and other 

wastes.

•	Site characteristics such as stockpile spacing,

soil, topography, access, and drainage channels, 

as well as nearby surface water, residences, 

businesses, and population densities.

•	 Site conditions impacting fire control, such as

access roadways, water resources, perimeter and 

internal fire lanes, trees, and brush.

The information on site characteristics and conditions 

is useful for site stabilization and fire control planning 

for larger sites. For smaller sites, only the location, 

owner or operator, and stockpile characteristic 

information is needed. 

Mapping

Stockpile mapping offers political, technical, and 

economic benefits. It allows public officials and 

citizens to understand the extent of the problem, as it 

graphically illustrates the broad distribution of scrap 

tire sites in the state. Mapping enhances efficiency by 

supporting coordination of site-related activities such 

as inspections. 

Quantity Estimation Techniques

After stockpiles have been identified, the scrap tire 

quantity is estimated for prioritization, program 

planning, budgeting, and contract management. 

Stockpile estimating is relatively simple in principle, 

but can be affected by many variables. 

During initial site identification and examination, 

the dimensions of each stockpile segment can be 

measured using one of several techniques, including 

a long tape, a measuring wheel, or a calibrated pace. 

A 100-foot fiberglass tape requires two people for 

efficient use and is preferable for uneven terrain or 

in cases likely to require court testimony. A largediameter measuring wheel can be used on firm, level 

terrain but is unusable on rough or muddy ground. 

A calibrated pace can be used efficiently on most 

terrain, but its accuracy depends on the ability of 

the measurer to maintain a uniform pace. Taking 

measurements from the midpoint of the pile slope 

simplifies subsequent calculations. In addition, 

photographs should be taken during field inspections 

to document site conditions, to monitor changes in 

site conditions between inspections, and to serve as 

legal evidence. 

Estimating stockpile depth is often a challenge 

because the sides are sloped and are not easily 

measured. One technique is to have a person of 

known height stand as close to the pile as possible 

while an observer stands back and measures the pile 

depth in multiples of the first person’s height. The 

observer should be at least 10 times the estimated pile 

depth away to minimize angle distortion. A spotter’s 

scope or compact measuring device can also be used. 

Climbing a large pile can help to collect information 

about top contours, pile characteristics, dimensions, 

and firmness (which reflects density variations 

associated with compaction, aging, and lacing). Tires 

in stockpiles are irregularly shaped, flexible, and 

Border 2012: U.S.-Mexico Border 

Scrap Tire Inventory and Mapping

In 2007, as a step toward improving scrap tire 

pile management along the U.S.-Mexico border, 

the USEPA Office of Solid Waste (Currently the 

Office of Resource Conservation and Recovery) 

initiated a project to create a comprehensive 

scrap tire pile site inventory. (Scrap tire pile sites 

include sites where tire piles exist or have recently 

been cleaned up.) The primary objective was to 

compile existing data to create an inventory of all 

known tire pile sites on the Mexican side of the 

eastern border (along New Mexico and Texas). 

In 2002, USEPA Region 9 prepared a tire pile 

inventory for the western border (along California 

and Arizona) for the United States and Mexico, 

which was updated in 2003 and 2004. After data 

collected on the Mexican side of the eastern 

border had been compiled, these and other 

available data were used to create one geographic 

information system (GIS) map of scrap tire pile 

sites for the border region. This information can 

be found at www.epa.gov/epawaste/conserve/

materials/tires/pubs/2012-tires.pdf. 

Mapping Tip

Review of site background information, such as 

aerial photographs, topographic maps, or tax 

maps, before the scrap tire quantity is estimated 

can reduce the effort needed for field mapping. 

This information is often available in government 

or other Internet-accessible databases. The USEPA 

Scrap Tire Cleanup Guidebook also contains a 

section on mapping, and the information can 

be found at www.epa.gov/epawaste/conserve/

materials/tires/pubs/2012-tires.pdf. 
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unstable, so extreme care should be taken in climbing 

a tire pile. Stockpiles pose other risks to estimators, 

including disease-carrying mosquitoes, rodents, 

and snakes. Estimators should be alert and move 

cautiously.

Aerial photographs can be used to define the 

dimensions for a large stockpile, but a scale must be 

established based on nearby objects. To be effective, 

aerial photographs must be taken vertically to avoid 

dimensional distortion. Depth and density estimation 

requires ground observation. Detailed aerial surveys 

can be conducted, but the ground topography under 

the pile must be known or assumed. Aerial surveys 

are expensive, and their accuracy is questionable 

unless a pile is deep enough to reduce the margin of 

error associated with irregularities in surface depth. 

As a first step, the stockpile volume is estimated using 

calculations based on the dimensions. In some cases, 

irregular shapes in the tire pile can be converted into 

rectangles, circles, or other simple geometric shapes 

to simplify calculations without impairing accuracy. 

In other cases, a single irregularly shaped pile can 

be measured as two or more connected rectangular 

segments with different dimensions. If dimensions 

have been measured from the midpoint of the slope, 

the volume of a rectangular pile is simply the total of 

multiplying the length, width, and depth. Although 

this method is not geometrically perfect, the 

simplification does not significantly alter the total 

volume estimate.

The second step in estimating the tire quantity in 

a stockpile is estimating the pile density, or the 

quantity of scrap tires contained in each cubic 

meter, or yard, of the pile. Volume is translated 

into quantity or weight through assignment 

of a density. Because most tire stockpiles 

contain mixtures of various tire sizes, density is 

normally expressed in terms of the passenger 

tire equivalent (PTE), which is equal to 9 kg (20 

pounds) by definition. The densities of most scrap 

tires are roughly equivalent when expressed in 

6‘

60‘

Determination of tire stockpile depth

Determination of tire stockpile volume

The volume of common stockpile shapes can be calculated

with the following formulas:

Circle

∏r2d = 3.14 x circle radius x circle radius x depth

Triangle

1⁄2 lwd = 1⁄2 x length x width at base x depth (from base to peak of pile)

Trapezoid

1⁄2 l (w1 + w2) d = 1⁄2 length x (width at base + width at top) x depth
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terms of PTE/cubic yard. For instance, a medium 

truck tire weighs approximately 45 kg (100 pounds 

or five PTE) and occupies a volume equivalent to 

four to five passenger tires in a given stockpile. The 

equivalency more accurately reflects future tire use, 

processing, and disposal because most abatement 

activities and other considerations are based on 

weight.

The density of loose, shallow, whole-tire stockpiles 

is normally about 10 PTE/cubic yard but can range 

from 8 to 27 PTE/cubic yard. Densities below 10 

PTE/cubic yard reflect rimmed tires that do not 

collapse but account for only the rubber weight 

under the assumption that rims will be removed 

before tires are transported. Stacking or lacing 

increases the effective density to 12 to 15 PTE/

cubic yard for passenger tires and to 13 to 18 PTE/

cubic yard for medium truck tires. 

The density of shredded-tire stockpiles can 

range from 30 to 90 PTE/cubic yard (600 to 

1,800 pounds/cubic yard). The lower density 

range represents shallow, un-compacted piles 

of uniformly large particles such as single-pass 

shreds. The higher range represents deep 

stockpiles of finer tire-derived fuel (TDF) that has 

been heavily compacted by repeated movement 

of heavy equipment during stacking. The highest 

range represents a mixture of compacted tire 

shreds and dirt. 

Once the stockpile volume and density have been 

estimated, the tire quantity (or weight) is calculated 

by multiplying the volume (cubic yards) by the 

density (PTE/cubic yard). The result is a tire quantity 

expressed as PTE. The tire quantity can also be 

expressed as a weight (tons) by dividing by 100 PTE/

ton. 

Although the estimating methodology described 

above has been successfully applied to hundreds of 

scrap tire stockpiles, the following factors may affect 

its accuracy:

•	 Topography: The underlying topography 

can significantly affect pile volume and tire 

quantity, but may not be apparent from surface 

observations. Larger tire piles are more difficult 

to estimate because they may conceal ravines or 

pits filled with tires. Piles located on hillsides are 

also difficult to estimate because hillsides may 

curve or become steeper beneath the piles.

•	 Non-uniformity: A pile may appear to consist 

of loose tires on the surface, but laced tires or 

shreds may be present in the pile, significantly 

increasing pile density and tire quantity.

•	 Contamination: Piles can be contaminated with 

water, soil, automobile parts, or other waste that 

may not be visible from the surface. Water and 

dirt can significantly increase pile density and 

abatement costs. 

Stockpile Prioritization

With the understanding that resources are limited, 

stockpile stabilization, abatement, or both, should be 

initiated following a prioritized sequence based on 

the comparative hazards posed by various sites. A 

prioritization system may reflect impacts on citizens 

and the environment, and particularly impacts on 

sensitive receptors such as schools, hospitals, daycare 

centers, and nursing homes.

One prioritization method uses stockpile size as a 

multiplier because it typically magnifies the impacts 

of a tire fire. The multiplier ranges should reflect the 

quantities of tires in the piles being prioritized. For 

example:

Less than 100,000 tires = 1

100,000 to 250,000 tires = 2

250,000 to 1,000,000 tires = 3

More than 1,000,000 tires = 4

Table 2-1. Pile Quantity Estimation: Whole vs. Shredded Factors Affecting Tire Density

Whole Tire Stockpile Shredded Tire Stockpile

Depth: Increases the compaction of tires in a pile and 

therefore increases density.

Age: Allows additional compaction over time and 

therefore increases density. 

Heat: Increases the flexibility of tire rubber, thereby 

increasing compaction and density.

Shred size: Smaller shred size generally increases 

density.

Wire content: Wire removal decreases density. 

Depth: Depth increases compaction and density 

caused by overlying tire shreds (pieces).

Equipment movement: Equipment movement on 

ramps or top surfaces during stacking significantly 

increases density as well as probability that the pile 

will spontaneously ignite. 
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The potential impact on the general categories 

of air, water, and population are often evaluated 

independently (based on data from the initial site 

evaluation) using a scale of 1 to 10, with 10 indicating 

the greatest potential impact. These three ratings are 

added and multiplied by the size factor. Stockpile 

size is an important consideration, but impact is the 

controlling issue.

Stockpile sites can then be prioritized based on 

the resulting rating totals, with the highest rating 

representing the highest priority. Sites generally 

fall into rating groups with numerical separations 

between the groups. Within groups, rating 

differences are generally small, and the abatement 

sequence can be based on site access, contractor 

availability, markets, or location. 

Consistency is an extremely important component 

of any stockpile prioritization system, so using the 

smallest possible number of evaluators will increase 

consistency. However, it can be beneficial for two 

or three evaluators to compare their ratings so that 

subjective inconsistencies can be identified and 

corrected. 

Some states use independent contractors or 

consultants to manage or perform stockpile 

prioritization to limit political influences. Using a 

technically sound prioritization process conducted 

by unbiased evaluators also improves program 

development. 

Property Issues 

Scrap tire stockpiles are generally located on 

property that is owned and controlled by one or 

more individuals. Before a scrap tire remediation 

project begins, it is essential to obtain either a 

written property access agreement from the 

landowner or a court order granting property 

access for tire removal. At many sites, a property 

boundary survey is also necessary to ensure 

that remediation work does not inadvertently 

extend onto adjacent properties. If additional 

properties are involved, additional property access 

agreements or court orders will be needed.

The following issues should be considered in 

dealing with properties:

•	 Utilization: A property can contain buildings, 

other structures, and public utilities, such as 

electricity, natural gas, water, and/or sewage, 

which could be useful to a contractor during 

on-site activities. If any of these items are to 

be used, a written agreement establishing use 

conditions, obligations, and compensation can 

prevent subsequent misunderstandings.

•	 Damage: States have been sued for damage 

done by contractors acting as their agents. 

In some cases, the damage has been done 

by others before cleanup began. As a 

preventive measure, complete and dated sets 

of photographs before, during, and after site 

abatement are useful for documenting site 

conditions.

Table 2-2. Factors to Consider When Evaluating Impacts of Scrap Tire Stockpiles

IMPACT AIR WATER POPULATION

ISSUE Impact of fire plume on 

residents, businesses, and 

regional air quality

Impact of the contaminants 

found in tire rubber and 

residual ash on surface water 

or groundwater 

Impact of existing stockpile 

on area residents

FACTORS TO 

CONSIDER

• Prevailing wind direction

• Stockpile characteristics such

as height, trees and brush, 

and fire lanes

• Surrounding land use

• Sensitive receptors such as

schools, airports, and large 

public facilities (within 0.5- 

and 5.0-mile perimeter)

• Soil characteristics such as

permeability

• Aquifer characteristics such

as water table depth and 

drinking water use

• Site drainage

• Surface water proximity

• Sensitive receptors such

as wetlands, fisheries, or 

endangered species

• Stockpile characteristics

• Population proximity

• Mosquito species

• Identified local/regional

mosquito-borne diseases

• Rodent/snake infestation

• Stockpile characteristics
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•	 Restoration: Water in tires and rain create 

muddy conditions in unstable soil under a 

stockpile. Heavy equipment can create deep 

ruts, and water runoff can erode surface soil. 

After tires have been retrieved, contractors are 

generally required to level heavily rutted land. 

In most cases, re-establishing vegetation will 

control erosion.

Recognizing a property’s value while obtaining and 

maintaining the landowner’s cooperation facilitates 

abatement operations. If the property owner will 

not cooperate, a court order must be obtained to 

enter the property and remove the scrap tires. State 

legislation can aid this process if laws are enacted to 

create an administrative process for ordering scrap 

tire cleanups. One example is Ohio Revised Code 

3734.85, which can be found at www.ohio.gov/

government.htm.

Communications

Stockpile abatement involves many groups, 

including contractors, local governments, 

politicians, and the press. Informing and 

coordinating these groups are critical to successful 

scrap tire programs and abatement projects.

Contractors

Any special abatement project requirements 

should be clearly defined in detailed plans and 

specifications provided to prospective contractors 

in advance of the bidding process. Examples of 

items that should be addressed in such plans are 

as follows: 

•	 Site description

•	 Tire quantity estimate

•	 Tire pile length, width, and height

•	 Operating procedures

•	 Fencing

•	 Lighting

•	 Security

•	 Fire lanes

•	 Pile removal sequence

•	 Stabilized access and perimeter roadways

•	 Control of vegetation, mosquitoes, and run-off

•	 Water source and distribution

•	 Fire plan

•	 Utilities

•	 Progress reporting

Many contractors have developed their own 

abatement methods to optimize the efficiency of 

cleanup operations based on years of experience. 

An initial description of the project should be 

developed to provide a sound foundation for project 

communications and to minimize the need for 

extraneous discussion of activities planned. Example 

pre-bid documents prepared by the States of Iowa 

and Illinois are available at www.epa.gov/reg5rcra/

wptdiv/solidwaste/tires/guidance/index.htm. 

Elected Officials

Local and state elected officials are instrumental 

in creating and maintaining abatement programs. 

Providing updates on program implementation and 

abatement projects is important. Inviting elected 

officials to view stockpile sites before and after 

cleanup creates a good public relations opportunity. 

Local Governments

Local administrators and police and fire departments 

can provide critical support services at little or no 

cost if they are included in project communications. 

Informing these groups about project plans and 

associated benefits to the community enhances 

cooperation. 

Partnerships

Inter- and intra-governmental department taskforces, 

public-private collaborations, and multinational 

partnerships are able to accomplish a great deal as 

they can encompass the entire area, pool assets and 

resources, and work together to create and carry 

out abatement programs. Enhancing cooperation 

and building relationships on both sides is an added 

benefit to these partnerships. Information on U.S. 

and Mexico scrap tire partnerships can be found at 

www.epa.gov/Border2012/fora/waste-forum/tires-done.

html and in the 12th report of the Good Neighbor 

Environmental Board at www.epa.gov/ocem/gneb/

gneb12threport/English-GNEB-12th-Report.pdf. 

Press

Publicity allows citizens to understand an abatement 

program and the value received for public fees. In 

addition, publicity allows politicians and program 

participants to be recognized for accomplishing 

removal objectives. However, drawing attention to 

stockpile abatement projects before the cleanup is 

finished can have undesired effects. For example, 

many fires are actually started by site operators or 

local residents in the wake of publicity over cleanup. 

One approach is to issue a press release highlighting 

the last scrap tire being thrown onto a truck by a 

local community leader; the release can include site 

photographs taken before and during abatement.
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Tire Initiative Collaborative Effort

Border states, municipalities, and the tire industry are working together to address the border’s tire 

problem through a Border 2012 initiative called the Tire Initiative Collaborative Effort. The purpose of the 

collaborative effort is to increase awareness and understanding of the U.S.-Mexico Scrap Tire Integrated 

Management Initiative, a scrap tire management framework.

Partners

Environmental Secretariats: On August 14, 2008, the heads of the environmental departments in all 10 

Border States formally signed a Tire Initiative Letter of Understanding at the Border Governors Conference 

in Hollywood, California. The 10 Border States include California, Arizona, New Mexico, Texas, Baja 

California, Sonora, Chihuahua, Coahuila, Nuevo Leon, and Tamaulipas. 

Border Governors: At the XXVI Annual Border Governors Conference, a joint declaration was signed by 

border state governors to execute the tire initiative among the Environment Worktable representatives. 

Border Municipalities: AA number of border municipalities have agreed to take steps to implement the 

Tire Initiative.

Border Legislative Conference: At the 16th Border Legislative Conference on October 19, 2007, state 

legislators from the U.S. and Mexico expressed their support for the tire initiative. 

Tire Industry: The U.S. and Mexican tire industries, represented by the U.S. Rubber Manufacturers 

Association (RMA) and the Mexican Chamber of Rubber, are committed to collaborating with the U.S. 

and Mexican governments to solve the tire problems on the US-Mexico border. RMA signed a letter of 

understanding on May 18, 2008. 

For a more detailed listing of current partnerships between the U.S. and Mexico visit www.epa.gov/

usmexicoborder/infrastructure/index.html. 

U.S.-Mexico Scrap Tire Integrated Management Initiative 

USEPA and SEMARNAT agree that implementation of the U.S.-Mexico Scrap Tire Integrated Management 

Initiative principles and actions are necessary for proper management of scrap tires in the U.S.-Mexico 

border region. The tire initiative was accepted by the Border 2012 Tire Group and signed by SEMARNAT and 

USEPA in October 2006. 

Tire Initiative Principles

Better understand the problems contributing to scrap tire generation

Prevent new tire piles

Clean up “legacy” (existing) tire piles by environmental sound and cost-effective solutions

Involve stakeholders and communities in creating solutions

Tire Initiative Actions

Gather information to better understand scrap tire generation.

Encourage development and implementation, through incentives, of environmentally acceptable and 

economically viable end-use markets for scrap tires to increase recycling and reuse.

Abate tire piles by seeking funding to eliminate existing scrap tire piles, and by investing in temporary 

storage/transfer stations to facilitate tire recycling and reuse.

Involve federal, state and local government, business, universities, and nongovernmental organizations in 

the implementation of the Scrap Tire Integrated Management Initiative.

Support educational outreach programs on scrap tire recycling and reuse targeting diverse groups of 

stakeholders.
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CONTRACTORS 

The success of a scrap tire abatement program hinges 

on selecting contractors capable of carrying out the 

required tasks cost effectively in accordance with 

procedures and schedules. In many early abatement 

efforts, scrap tire processors were developing field 

operating experience, equipment was evolving, 

maintenance requirements were being defined, 

limited capital prevented use of efficient tire retrieval 

equipment, and few product markets existed, 

leading to project delays and failures. Although 

abatement still poses substantial challenges, the 

cumulative benefit of past experience, equipment 

improvements, appropriate retrieval equipment, 

and substantial market development has greatly 

enhanced the probability of success. One key 

to success is selection of contractors with good 

performance records and the ability to perform at a 

reasonable cost. This section defines critical factors 

and alternatives for successful evaluation and 

selection of stockpile abatement contractors.

Evaluating Contractor Qualifications

The amount of information requested from 

contractors during the evaluation process 

varies widely. Some state agencies request 

comprehensive data, while others simply request 

contact and pricing information. Below are the 

primary factors that have been used to evaluate 

contractors: 

Company History

Some contractors and processors have changed 

their names frequently, especially after failed 

projects. Requiring a contractor to identify all of 

its previous names and affiliated companies and to 

provide organizational charts can help the agency 

understand the contractor’s history. 

Company Financial Capabilities

Financial strength increases the probability that a 

contractor will have appropriate equipment and 

will be able to overcome unexpected problems. To 

identify the financial strength of contractors, some 

states request 2 or 3 years of financial data. Some 

privately held companies are reluctant to provide 

these data unless confidentiality can be maintained. 

An alternative is to require a contractor to document 

its ability to provide a bond or other financial 

assurance for an amount equal to the maximum 

required for the proposed abatement activities. This 

approach protects the agency’s financial interests and 

avoids confidentiality concerns.

Experience

Positive project experience increases the probability 

of future success, so it is critical for a contractor to 

document its experience on comparable projects. A 

contractor should describe its previous work in detail 

and should submit customer contact information to 

allow the agency to verify performance claims.

Equipment

Stockpile abatement involves tire retrieval, transport, 

and processing. Requiring a contractor to list and 

describe the major equipment to be used facilitates 

the evaluation. Retrieval equipment generally 

includes an excavator for larger sites, a front-end 

loader with a specially equipped bucket system for 

medium-sized sites, and a tracked bobcat with an 

appropriate bucket for smaller sites. 

Transport equipment typically consists of standard 

18-wheel trucks and trailers. High-volume trailers 

enhance efficiency if long-distance transport of whole 

tires is required. Some contractors use subcontractors 

to haul tires; information on the subcontractors, such 

as their licensing or relevant qualifications, should be 

required during the bidding process.

Tires can be processed on site or at a centralized 

processing facility. Processing equipment 

requirements depend on product and market 

specifications. A smaller product size specification 

normally requires multiple-size reduction units in 

series or extensive re-processing within a single 

unit (with a proportional decrease in effective 

capacity). The impact of dirt, rocks, and other 

contamination is generally proportional to the 

processing requirements. Large tire chips for highway 

embankment applications require less processing, 

but soil contamination must be removed. Nominal 

1-inch-diameter TDF has been produced at stockpile 

Improperly discarded tires

Photo courtesy of Brian Wright, Georgia
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sites, but dirt contamination significantly increases 

equipment maintenance requirements and associated 

downtime. It is generally not possible to produce 

crumb rubber from stockpiled tires unless they are 

unusually clean and are carefully retrieved.

Products and Markets

A contractor should be required to identify the 

intended uses for processed scrap tires and what 

percentage of the products is expected to be from 

stockpiled tires. In general, this percentage should 

not exceed 15 to 25 percent of the current-generation 

tires. In addition, the contractor should identify 

product specifications and an existing contractual 

basis with a customer who wants the processed scrap 

tire product. Lack of a contractual basis increases 

market vulnerability and the probability that products 

made from current-generation tires will be displaced. 

The proposed processing equipment must be capable 

of generating products that meet the specifications. 

Wastes

In some cases, contractors have received premium 

payments associated with scrap tire recycling while 

actually recovering only a very small percentage 

of tires as usable product. Substantial volumes of 

tires have been discarded or landfilled without the 

prior knowledge of the contracting governmental 

department. For this reason, a contractor should 

identify projected waste volumes and disposal 

methods so that the contracting governmental 

department can consider recovery percentages in 

its evaluation. On the other hand, the contracting 

department should not preclude landfill disposal of 

heavily contaminated tires or shreds. 

Personnel

A contractor should identify specific management 

personnel and their prior experience, including the 

on-site personnel who will be responsible for daily 

operations and equipment maintenance. 

Availability

Many contractors have limited equipment and may 

be involved with multiple sites prior to a new contract 

award. For this reason, a contractor should identify 

its anticipated mobilization time requirement and 

proposed start date; alternatively, an early start date 

can be established to reveal whether a contractor can 

perform according to the schedule. 

Cost

The contracting department can require a contractor 

to submit a bid based on a fixed price for the total site 

abatement. In general, contractors build a substantial 

safety factor into fixed-price bids, increasing the cost 

per ton of material to be removed. Most current 

abatement activities are performed on a cost per 

ton basis to enhance cost effectiveness. The risk 

associated with this approach involves additional 

costs associated with contamination, such as soil or 

automotive parts. To control abuse, retrieval and 

loading operations should be closely monitored, and 

the contracting department should reserve the right 

to adjust weights to control excess contamination. 

Bidding and Award Process

States have used a wide range of approaches in 

the contractor bidding and award process. One 

major variable has been the amount of information 

requested in request for proposal (RFP) documents. 

In some cases, only a fixed price was requested, 

and the project was awarded solely on this basis. 

One state used this approach during initial site 

abatement activities, and the contractors selected 

were inexperienced, underfinanced, and offered 

low bids based on a misunderstanding of the 

abatement requirements. 

An alternative RFP approach for major stockpile 

sites is to require contractors to provide 

detailed responses to the criteria cited in the 

previous subsection to increase the factual 

basis for evaluation. Less information may 

be requested for smaller sites or when the 

contracting department already has a thorough 

understanding of a contractor’s capabilities based 

on previous experience. Each criterion included 

in the RFP should be weighted based on their 

importance. A minimum of three experienced 

staff should evaluate and score proposals, with the 

total scores controlling contractor selection. 

Conducting a detailed RFP process for each site 

can be cumbersome and time-consuming for 

all parties, especially if multiple sites are to be 

abated. An alternative is to pre-qualify potential 

contractors through a modified RFP or a request 

for qualifications (RFQ) process. Florida has used 

a pre-qualification process successfully since 1989. 

The process is repeated every 3 to 4 years to allow 

for changes in industry participants. Illinois relies on 

a similar pre-qualification process so that contractor 

responses include binding cost data presented on 

a price per ton basis. When a site is identified for 

abatement, a contractor is selected based on the 

site’s proximity to the contractor’s processing facility. 

The lack of individual site bidding does not result in 

significantly higher abatement costs.
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Contracts

The form of an abatement contract depends on 

the bidding and award procedures used as well as 

state contracting requirements. There are two main 

categories of contracts:

•	 Individual site contracts created solely to cover

specified abatement activities associated with 

an individual or conjoined stockpile. These 

contracts are typically awarded based on singlesite RFP responses.

•	 Task assignment contracts created to cover

general conditions associated with stockpile 

abatement at more than one site. These 

contracts are supplemented by task assignment 

documents covering specific site conditions as 

awards are made. 

Each state has its own contracting procedures 

and contract requirements, so it is not possible to 

provide a “model” contract. However, examples of 

basic contract documents are available at www.

epa.gov/reg5rcra/wptdiv/solidwaste/tires/guidance/

index.htm. 

Bonding and Insurance

The primary purpose of bonding and insurance 

requirements is to protect the contracting 

government agency from financial loss as a 

result of contractor error or failure to perform. A 

secondary purpose is to ensure that a contractor 

has adequate resources and is committed to 

successful project completion.

Historically, contracting agencies have required 

bonding or other financial assurance equivalent 

to 50 to 100 percent of a project’s estimated cost. 

In addition, a bond typically remains in force until 

the contracting agency confirms final project 

completion and releases the bond. When bonds 

were relatively easy and inexpensive to obtain, 

the bonding requirement was not normally a 

hardship, except for companies with poor operating 

statements or balance sheets.

Recently, however, it has become more difficult 

and expensive for smaller companies (including 

many successful contractors) to obtain bonds. Some 

companies have resorted to alternative methods 

such as letters of credit or cash deposits. In some 

cases, large financial assurance requirements can be 

burdensome for contractors, as they tie up working 

capital resources needed to execute contracts. 

In other cases, these requirements may exclude 

experienced contractors from competing. Iowa and 

Virginia have no financial assurance requirements 

and have not experienced any contractor failures, 

but these states have a long history of successful 

contractor performance. 

Capacity Assessment

The tire processing industry and product markets 

have a finite capacity to process and use currentgeneration tires and tires from stockpile abatement. 

Abatement objectives should consider the context 

of local and regional capacity to avoid disrupting 

the market. For instance, if the capacity of local or 

regional processors is limited, they can be made 

aware of anticipated tire volumes and may choose 

to increase their capacity. If not, mobile processors 

can be solicited from a broader geographic area. If 

markets are limited, others can be created through 

government cooperation or incentives. For example, 

New York considers use of tire chips from stockpile 

abatement for embankment projects if the chips 

have a lower delivered cost than other aggregate 

alternatives. If economic imbalances are not 

correctable, program objectives should be adjusted to 

reflect realistic tire volumes or to allow tire disposal to 

avoid market disruption. 

On a smaller scale, assessing a contractor’s processing 

and marketing capability to absorb stockpiled tires 

without disrupting use of currently generated tires 

can be a reality check on contractor projections. 

Identification of processing capacity should be based 

on the historically demonstrated performance of 

similar processing equipment, and not on equipment 

supplier claims.

PROJECT MANAGEMENT

The preceding sections provide the foundation and 

considerations for establishing a successful scrap 

tire abatement program based on the experiences 

of U.S. states. However, once abatement projects are 

under way, new issues arise. This section discusses 

factors that will enhance project management and 

implementation.

Site Survey

Before site mobilization, the property boundaries 

should be reviewed or surveyed to verify that all 

tires and planned access routes are located on the 

property. Often, tire piles extend across property 

lines. In these cases, written property access 

agreements with neighboring property owners will 

be needed. 
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Equipment

Proper equipment selection depends on site 

conditions, and unique site conditions may require 

specialized equipment or safety procedures. For 

instance, a tracked excavator is an efficient, highvolume tire retrieval tool if the following conditions 

exist:

•	 Open-top trailers can be moved adjacent to the

stockpile for direct loading, minimizing excavator 

movement. 

•	 Boom (arm and bucket of excavator) movement

is not impaired by large trees or other obstacles 

such as power lines. 

•	 The stockpile is deep, but the top is reachable. 

•	 Contaminating metal objects are large enough to

be seen and separated prior to loading. 

•	 The bucket is closed above ground level to

minimize soil entrapment. 

In some cases, smaller equipment such as a loader or 

tracked bobcat can be more efficient and inexpensive 

than an excavator. For instance, an excavator loses 

many of its advantages if tires are simply being staged 

for loading into enclosed trailers. A skid loader can 

easily place tires in the end of a trailer. In addition, 

changing site conditions can alter equipment needs 

during a project. Contractors need the flexibility 

to make adjustments, provided that the schedule 

and safety are not compromised and no increased 

contamination or site damage results.

Transportation

Registration and Permitting – Many states require 

processor and hauler registration. All necessary 

registrations and permits should be obtained ahead 

of time to avoid unnecessary delays. 

Weighing – Load weight can change during 

transport. Trapped water can drain during tire 

movement, or rain can add weight if water is trapped 

in exposed tire casings. In other cases, tires may 

be added to trailers in transit. If possible, trailers 

should be weighed at a pre-approved scale near the 

abatement site and again at the receiving site. The 

lower of the two weights should be used for invoicing. 

Tire Rims – Rims can double the transport weight of 

passenger tires. Removing rims prior to transport will 

reduce transport and processing charges based on 

weight. If rim removal is not feasible, a tracking and 

weight adjustment method should be established, 

especially for sites such as salvage yards that have 

high percentages of rimmed tires. When tires are 

de-rimmed, both the scrap metal rims and the tirebalancing lead weights removed provide a source 

of revenue. The contract terms should clearly state 

whether the contractor retains this revenue, shares 

the revenue with the government department, or 

submits all the revenue to the department. 

Rail Transport – Transportation of shredded tires in 

bottom-dump railcars can be problematic if chips 

compact and rainwater freezes. The chips then 

become difficult to dump at the receiving site. 

Side-dump and arm-dump railcars generally do not 

encounter this problem. 

Monitoring Logs – Up-to-date records of scale 

tare (empty container) weights and loaded weights 

must be kept for all vehicles. Unit numbers must 

be noted on weigh slips to avoid discrepancies that 

can delay invoice payments.

Environmental Factors

Water

Water can create serious problems at a stockpile 

site. Storm water can accumulate in low spots, 

impeding equipment movement and operating 

efficiency. Also stockpiled tires spill trapped water 

during retrieval and handling, creating unstable 

soil at the site. These problems can be resolved 

by creating drainage channels or constructing 

elevated paths for equipment. An alternative is 

to rotate work areas to allow wet, unstable areas 

to dry. As unstable ground is exposed under 

piles, silty runoff can drain from the property 

to adjacent streams, ponds, and properties. Silt 

fences can prevent this type of runoff from the 

project site. 

Roadways

Heavy truck movement can destroy dirt roadways 

at sites during wet or thaw periods. If used by area 

residents, the road surface must be kept passable 

for normal vehicles.

Dust

During dry conditions, equipment movement 

on unstable soil and roadways can generate 

dust plumes. If airborne dust affects abatement 

operations, on-site personnel, or adjacent properties, 

water can be sprayed for dust control. 

Noise

Tractor-trailers, heavy tire-retrieval equipment, and 

on-site shredders are noisy. In populated areas, 

abatement operations can be limited to daylight 

hours to control noise impacts on nearby residents. 
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Security

The primary objectives of site security are to prevent 

the addition of tires to a site, prevent fires, and 

protect equipment. The security measures discussed 

below have been effective in accomplishing these 

objectives.

Vehicle Access Control

The most common approach for vehicle access 

control is a locked chain extending between secure 

posts. The chain can be removed for inspection or 

abatement, and most emergency response vehicles 

carry lock cutters in the event that they require 

access to a secured location. 

Fencing

Preventing all vehicle and pedestrian access to a site 

is difficult, but casual access can be controlled by 

fencing. Chain-link fencing and gates may already 

be present at industrial sites. A rural site may have 

multiple entrance points, so the entire perimeter 

should be checked for signs of unauthorized 

activity. 

Lighting

Lighting increases the probability that intruders 

will be observed but is effective only when 

combined with security guards. 

Security Guards

Security guards can control site access and 

provide an early warning in the event that a 

fire occurs. To be effective, guards must have 

adequate lighting and must patrol the site in spite 

of mosquitoes and adverse weather conditions.

Additional Measures

Guard dogs can deter intruders at fenced sites, but 

dogs raise liability issues and can be injured by 

loose wire at processing sites. Motion detectors 

have been considered for sites, but animal 

movement in rural areas triggers false alarms. 

Cameras have been used at sites but generally 

fail to provide adequate picture quality to support 

capture or arrest of an intruder. Smoke detectors 

and heat sensors have been considered for fire 

detection, but the associated expenses and logistics 

are problematic for abatement sites.

Fire Planning and Prevention

The greatest risk associated with scrap tire stockpiles 

is their possible ignition. Once ignited, stockpile fires 

tend to spread rapidly, generating massive quantities 

of smoke, oil, and contaminated soil and water that 

cause environmental damage. Factors associated 

with stockpile fire planning and prevention are 

discussed below.

Owner or Operator Role

Many stockpile fires involving arson start during 

enforcement proceedings to require cleanup or 

initial abatement activities. This indicates that the 

landowner may be seeking revenge or attempting to 

avoid paying for his share of abatement costs. As a 

general rule, it is five to 10 times more expensive to 

remediate a scrap tire site contaminated by a fire than 

to simply remove the tires. 

Emergency Response Plan

An emergency response plan should be developed 

for a large stockpile site to support coordinated 

notification and response in the event of a tire fire. 

Initial Site Stabilization

Large stockpile sites should be stabilized to decrease 

the possibility of a tire fire and to increase the odds 

of controlling a fire. Stabilization can be initiated by 

a site owner as part of a compliance agreement or by 

a contractor during the initial abatement. Important 

site stabilization activities include the following:

•	 Removal of trees, brush, and grass around

stockpiles to avoid fire transmission to and from 

surrounding areas, especially if the site is inactive.

•	 Identification of available fire control resources

and installation of supplemental fire control 

tools.

•	 Creation of at least two connected access points

for emergency vehicles.

•	 Creation of fire lanes that are at least 15 meters

(50 feet) wide to divide a large stockpile into 

isolated segments. The initial lane should 

roughly bisect the pile, and subsequent lanes 

should result in pile segments that are no larger 

than 15 by 60 meters (50 by 200 feet) in size. Pile 

sides should be tapered to avoid collapse during 

fire turbulence.

•	 Stabilization of central fire lanes to facilitate

access by emergency response vehicles and 

to maximize contractor efficiency during 

subsequent abatement activities.

Site Abatement

During site abatement, alternate pile segments 

should be sequentially removed to increase 

separation between remaining segments.
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Shred Auto-Ignition

Deep stockpiles of compacted tire shreds can 

undergo a progressive series of exothermic reactions 

that increase pile temperatures and pyrolytically 

generate combustible gases. Surface symptoms of 

this phenomenon can be subtle, such as a slight sulfur 

odor, vapor steaming from isolated sections of the 

pile surface, or slight oil sheen on adjacent standing 

water after rainfall. Auto-ignition normally occurs 

in stockpiles that are more than 10 feet deep and 

that have been compacted by movement of heavy 

equipment during their formation. The phenomenon 

has occurred in shreds of all sizes but is more 

common in smaller shred sizes. 

The potential consequence of auto-ignition is that 

surface fires can ignite on a shred stockpile, especially 

as the pile is abated. As shreds are removed from the 

area near the hot zone, gases and shreds are exposed 

to air and ignite. The fire then spreads across the 

pile as though it was started on the surface, as has 

occurred in more than 20 stockpiles and monofills. 

A sign of this phenomenon is an area of melted 

rubber shaped like a mushroom cap within the pile. 

Care should be taken during abatement of deep, 

compacted shred piles, and steps should be taken to 

immediately control auto-ignited shred fires before 

they can spread.

Communication

Successful abatement of a stockpile site depends on 

good communication between the contractor and the 

contracting government department. Both efficiency 

and mutual respect are acquired from experience, 

which is critical to successful tire abatement projects 

and programs. On-site monitoring and invoicing 

are also important elements of communication, as 

discussed below.

Contractor and Government Department 

Communication

Abatement plans and schedules are working 

documents that are subject to change based on 

factors such as weather, equipment breakdowns, and 

market conditions. Good communication between 

the contractor and the contracting agency provides 

a foundation for appropriate adjustments. The 

contractor can provide a weekly, biweekly, or monthly 

written progress report describing tire quantities 

removed, adherence to the schedule, obstacles, 

adjustments, and anticipated future activities. 

Progress reports may also be made verbally at the 

department’s discretion. 

On-Site Monitoring

Performance monitoring is a balance of economics, 

need, availability, and experience. States have used 

full-time monitors, facilitated daily visits by local 

officials, reviewed logs kept by security, or contractor 

personnel, and conducted unannounced site visits 

and record audits. 

Invoices

The contractor should submit monthly invoices 

with all supporting documentation. This procedure 

allows problems to be identified early and limits the 

amount of invoice preparation and review time. 

Site Restoration

Abatement Completion

The issue of abatement completion is subject to 

interpretation when tires are buried on a site. In 

general, large pockets of tires are removed but 

individual tires are left in place if less than 25 

percent of the tire extends above the surface. In 

cases involving tire shreds, some states require the 

contractor to use a 2-inch rake harrow to gather 

and remove surface shreds.

Other Wastes

Other waste materials present in tire stockpiles 

are normally separated and placed in piles. In 

some cases, wastes are segregated to facilitate 

subsequent recovery (for example, of metals) 

or disposal efforts. A contractor’s responsibility 

for other wastes should be clearly defined in the 

initial scope description. The contractor should 

receive supplemental compensation for wasterelated activities outside the scope.

Grading

A site can be deeply rutted by heavy equipment 

during abatement. The contractor is generally 

required to restore a relatively smooth surface 

corresponding to the original site contour.

Roadways

Public dirt roadways rutted by heavily laden trucks 

during abatement are generally graded at the end 

of on-site activities. County road crews are often 

assigned to this grading at little or no cost as a show 

of cooperation. Access roadways constructed to 

facilitate the abatement are sometimes removed.

Erosion Control

Seeding and drainage channels can control erosion of 

unstable surface soil. Silt screens or similar methods 

are used to control site runoff to adjacent surface 

waters until vegetation is re-established.
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Documentation

Post-abatement site conditions should be thoroughly 

documented by means of photographs or video 

recordings of ground conditions, residual piles, 

buildings, and fences. The documentation should be 

retained to aid in resolution any subsequent problems 

or issues.

SUMMARY

Many states in the United States have successfully 

cleaned up scrap tire stockpiles and established 

programs to prevent future formation of stockpiles. 

Much can be learned from the successes and failures 

of the wide array of strategies used to address 

this serious problem. This chapter is an effort to 

capture and share the collective knowledge of U.S. 

state and industry representatives with decades of 

experience in stockpile abatement 

Many U.S. states have demonstrated that the 

threats to human health and the environment 

posed by uncontrolled and illegal scrap tire 

stockpiles can be mitigated. This can be done 

through thoughtful application of regulatory 

policy and available resources along with 

careful planning and execution of cleanup 

projects. Based on the experiences of state and 

federal authorities in the U.S., the costs of stockpile 

prevention and abatement are small fractions of 

the costs associated with emergency response and 

remediation necessitated by tire fires.

This chapter has provided an outline of the essential 

elements that states have considered in planning and 

implementing abatement programs and individual 

cleanup projects. After decades of catastrophic 

tire fires and other health-related impacts of illegal 

scrap tire piles, it is clear that these practices can 

be effective in protecting human health and the 

environment from these hazards. 

Large scale scrap tire pile fire

Photo courtesy of Todd Thalhamer, California IWMB
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Chapter 3: Ground Rubber Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

CHAPTER 3

Ground Rubber

Ground rubber, or crumb rubber, results from the size 

reduction of scrap tires or other rubber products. The 

processing of tires into ground rubber can be done 

by machinery to shred or grind them and sorting 

the resulting pieces which will determine its use. 

Additional processing may be necessary to remove 

all metal beading dependent on its intended market. 

After processing the resulting tire pieces generally 

range in size from about 40 mesh to about 6 cm 

(1/4 inch). Ground rubber can be used for a wide 

variety of products, ranging from animal mattresses 

and traffic cones to athletic surfaces and as additive 

to asphalt, each of which will be discussed in this 

chapter. 

Within the traditional recycling hierarchy, the 

highest-value applications (the special uses to which 

scrap tires are put) for scrap tires use ground rubber 

itself for its specific performance characteristics. 

To maximize the value of scrap tire resources, 

tremendous financial, technical, and creative 

resources have been devoted to developing tire 

processing technology to make ground rubber and 

applications to use it. Results have been mixed, 

however. The Rubber Manufacturers Association 

estimates that, after more than 20 years of concerted 

effort, only about 17 percent of the waste tires 

generated in the United States in 2007 were 

processed into ground rubber for use in many creative 

applications (Ref.1). Since these applications have 

historically developed slowly and do not consume 

enough tires, they cannot be the primary focus of a 

new scrap tire management program. However, they 

remain a sound recycling option and an important 

component of market diversity.

The energy and civil engineering markets are larger 

and can be developed more rapidly, so they deserve 

initial program focus to accelerate full use of waste 

tire resources. As a result, this guide focuses 

on these applications. However, major ground 

rubber markets can be identified and developed 

concurrently. In addition, with the experience 

gained in the United States, it may be possible to 

accelerate market growth in Mexico. 

Initial development of civil engineering and tirederived fuel (TDF) applications will not prevent 

ground rubber processors from obtaining scrap 

tires as needed in the future. As ground rubber 

markets develop, waste tires will naturally be 

diverted to products with higher value. Ground 

rubber products generate higher product 

revenue, allowing processors to attract waste 

tires by charging lower tipping fees. Waste tires 

generally move to the lowest-cost disposal or 

recycling option, so higher- markets like ground 

rubber naturally displace lower-value civil 

engineering and TDF markets.

MAJOR U.S. GROUND RUBBER 

MARKETS

Previous experience in the United States does not 

necessarily translate into future markets in Mexico. 

However, it can provide examples of applications 

that have a proven ability to be manufactured 

and a willingness by consumers to purchase, 

two critical components of market development. 

Applications for ground rubber are normally 

grouped into the following major market segments:

Athletic/recreational surfaces – Use in artificial 

sports turf, natural (grass) turf and playground 

cushioning to protect children when they fall.

Molded and extruded products – Many products, 

including mats, bumpers, and other creative products.

Rubber modified asphalt and sealants – Addition of 

ground rubber to asphalt binder to improve highway 

performance characteristics, including how long the 

road will last.

Tires/Automotive – Use of ground rubber from 

scrap tires in manufacturing new tires, in the rubber 

Exhibit 3-1. U.S. Ground Rubber Market Distribution

Source: Rubber Manufacturers Association

Molded/ 

extruded

Tires/ 

Automotive Export Other

Athletic/ 

Recreational

Asphalt
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Chapter 3: Ground Rubber Scrap Tires: Handbook on Recycling Applications and

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compounds used to retread worn tires, and in molded 

automobile parts.

Other (Primarily Coarse Rubber) – Ground rubber 

is used primarily as colored mulch in landscaping 

applications.

Export – Ground rubber sold to markets in Europe 

and East Asia from the United States.

The percentage of ground rubber used in each of the 

major market segments in 2007 is shown in Exhibit 

3-1, based on estimates made by the U.S. Rubber 

Manufacturers Association (Ref. 1).

The following sections are intended to identify and 

briefly describe major market segments, focusing 

on those with the highest growth rate in the 

United States and the greatest potential for initial 

development in other countries, for example, 

Mexico. 

ATHLETIC AND RECREATIONAL 

SURFACES MARKET

Athletic and recreational surfaces currently 

represent one of the largest and most rapidly 

growing markets for ground rubber in the United 

States. This market segment encompasses a wide 

variety of applications and additional variations 

within them. The following discussion briefly 

summarizes the two largest applications within 

this market segment: synthetic sports turf, and 

playground safety surfacing.

Synthetic Sports Turf

Natural grass is a traditional sports field mainstay, 

but increasing usage of limited grass fields leads 

to turf failure, athletic injuries, and unattractive 

appearance of the field. In addition, standing 

water during wet weather can prevent use of grass 

fields and damage the field. Good grass surfaces 

require routine watering, fertilizing, and turf 

replacement, resulting in significant maintenance 

costs. Damaged grass surfaces may contribute 

to injuries when the ground is hard, muddy, or 

loses traction. Awareness of costs associated with 

maintenance and injuries has led to development of 

alternatives. 

Initial synthetic sports surfaces were developed 

for indoor arenas where the absence of sunlight 

prevented use of natural turf. One of the early 

examples was the Astrodome in Houston, Texas, 

which caused the trademarked name Astroturf to 

become a generic description for an early generation 

of artificial playing surfaces. More sophisticated 

systems that use ground rubber were developed in 

the 1990s to overcome some of the issues associated 

with the initial artificial surfaces. These advanced 

turf systems were initially applied in high-profile U.S. 

football stadiums used by professional and major 

university teams but are now in broad use on a wide 

range of sports fields at all levels of play. 

Description

The current generation of artificial sports turf uses 

7.6-cm (3-inch)-long strands of green polyethylene 

embedded in a porous backing to form a carpetlike structural framework for the turf system. The 

carpet is spread over a sophisticated drainage system 

capable of removing rain water rapidly and is in-filled 

with silica sand, ground rubber, or layers of each. A 

schematic representation of the FieldTurf Tarkett 

design is shown in Exhibit 3-2.

The result is an attractive turf that drains water 

rapidly and is capable of withstanding comparatively 

heavy use. The polyethylene grass-like blades add 

containment to the ground rubber, and the rubber 

provides cushioning while the combined synthetic 

turf system bears the physical forces of athletic 

activity. The backing — which holds the polyethylene 

blades, the blades themselves, the ground rubber, 

Exhibit 3-2. Field turf cross section

Photo courtesy of FieldTurf Tarkett

Berry Stadium, Cy-Fair Independent School District, Houston, Texas 

Photo courtesy of Terry Gray, TAG
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and other parameters of the turf system can be varied 

to achieve different performance characteristics for 

specific sports. Each manufacturer has variations 

intended to offer technical or economic advantages. 

An example of a U.S. football field is shown at the 

right. 

Current Market Status

Synthetic sports turf has grown rapidly to an 

estimated 1,000 field installations in 2008 in North 

America and hundreds more in Europe, according to 

the Synthetic Turf Council (www.syntheticturfcouncil.

org). These installations range from large stadiums 

to smaller municipal playing fields. The turf has been 

installed for international football, American football, 

field hockey, baseball, other sports, and practice 

facilities. The company FieldTurf Tarkett is one of the 

earliest manufacturers of synthetic sports fields and 

is believed to have installed more than half of these 

fields. Other companies with established roles 

in the sports field market include General Sports, 

IC Improvements, Sportexe, Sprint Turf, and other 

Necaxa Soccer Club field in which ground rubber 

was used to create synthetic turf

Photo courtesy of FieldTurf Tarkett

Table 3-1. Partial List of Synthetic Turf Installations in Mexico

Project Name City Country Year 

Pyesa Tenis-TV Azteca Monterrey Mexico R2003 

Tec de Monterrey CEM Guanajuato Mexico 04/07/2008 

Centro Asturiano de Mexico Ciudad de Mexico Mexico 09/25/2007 

Centro Asturiano de Mexico-Field #5 Mexico City Mexico 09/21/2007 

Centro Asturiano de Mexico-Field #4 Mexico City Mexico 09/21/2007 

Centro Asturiano de Mexico-Field #3 Mexico Mexico 09/21/2007 

Mas Futbol Leon Leon Mexico 10/18/2006 

Unidad Deportiva Valenciana-Field 2 Guanajuato Mexico 06/07/2006 

Unidad Deportiva Valenciana-Field 7 Guanajuato Mexico 05/10/2006 

Unidad Deportiva Valenciana-Field 1 Guanajuato Mexico 05/10/2006 

Unidad Deportiva Valenciana-Base ball Guanajuato Mexico 03/29/2006 

Mario Castro Field-Sport 7 Queretaro Mexico 01/24/2006 

Soccer City Querataro-Field 2 Querétaro Mexico 01/14/2006 

Soccer City Celaya Celaya Mexico 01/05/2006 

Soccer Society Aguas Calientes Guanajuato Mexico 12/15/2005 

Roberto Pina Field Guanajuato Mexico 11/14/2005 

Futura Soccer Veracruz Mexico 11/05/2005 

Charrua Field Charrua Mexico 09/30/2005 

Dinamo Irapuato Field Irapuato Mexico 09/12/2005 

John F. Kennedy School-Tampico Field Tampico Mexico 09/02/2005 

John F. Kennedy School-Main Field Queretaro Mexico 08/25/2005 

Sportfield/AstroPlay Inventory Mexico City Mexico N2003 

Colegio Marcelina Queretaro Mexico R2003 

University of Toluca Toluca Mexico R2003

Soluciones Industriales Queretaro Mexico 2007-2008

Perfect Tu Cancha Guatemala City Guatemala 2007-2008 

Canchas Sinteticas Tegucigalpa Honduras 2005-2008
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significant participants. Many of these companies 

sponsor web sites identifying regional offices, 

representatives, and authorized installers.

A partial list of installations in Mexico is provided in 

Table 3-1. This list is not complete, but it indicates 

that there are more than 30 installations in major 

stadiums and venues in Mexico. 

The Necaxa Soccer Club facility, installed in 2003 

in Aguascalientes, Mexico, is shown below as an 

example. Some of these installations have been in 

place for more than 10 years, providing a base of 

local experience. Furthermore, some of the systems 

have been tested and approved by the Fédération 

Internationale de Football Association (FIFA, the 

International Federation of Association Football in 

Zurich, Switzerland) governing body for their grasslike performance.

Ground Rubber Requirements

Each of the major synthetic turf systems uses 

ground rubber as the primary infill material 

surrounding the green polyethylene blades. 

The type and size of the ground rubber vary 

depending on the turf manufacturer. Some use 

primarily cryogenic ground rubber produced by 

freezing shredded rubber before it is fractured 

in a high-speed hammermill, a machine that 

pulverizes the rubber into fine particles. The 

resulting product has smooth sides and tends to 

flow easily when applied to a sports field. Others 

use “ambient” rubber, produced in a series of 

shear and compression equipment at ambient 

temperatures. This product tends to have a more 

irregular surface shape with a more cohesive 

consistency. A “crambient” product made by a 

primary cryogenic process followed by secondary 

ambient processing to yield hybrid performance 

characteristics is also used. 

Piece size requirements for ground rubber also 

vary by turf manufacturer. The most common 

distributions of piece sizes for sports fields are 14-

30 mesh and 10-14 mesh. “Mesh” is a term used to 

describe size and is equal to the number of holes 

per inch that the material can pass through. The 

specifications also generally require removal of 

virtually all the reinforcing fabric and wire that is 

initially present in scrap tires. Experience has shown 

that proper quality control of the ground rubber is 

critical for proper performance of synthetic turf.

Approximately 3 pounds of ground rubber are 

generally used per square foot of synthetic turf, 

depending on the manufacturer, design, and desired 

surface characteristics. As a result, the estimated 

1,000 new fields in North America with an average 

size of about 7,500 square meters (80,000 square 

feet) would be expected to use about 110 million 

kilograms (240 million pounds) of ground rubber in 

2008. This amount represents continuing growth 

from the Rubber Manufacturers Association’s estimate 

of 800 fields installed in 2007. It is also one of the 

largest individual ground rubber markets. Industry 

participants feel that the market has further potential 

for growth and has not reached maximum demand.

Application Benefits and Issues

Virtually any product has advantages and 

disadvantages, and questions are commonly 

raised about new products. Synthetic sports turf 

manufacturers claim their products offer the following 

advantages versus traditional grass turf: 

•	 Injury/Health - Synthetic turf remains consistent 

under varying weather, use, and maintenance 

conditions. According to a National Collegiate 

Athletic Association (NCAA) study that compared 

injury rates during the 2003-2004 academic year, 

the injury rate during practice was 4.4 percent 

on natural turf and 3.5 percent on synthetic turf 

(Ref. 2). Other studies indicate that frequency 

of injury is similar for both surfaces, but that 

the severity of injuries is worse on natural grass 

turf. There are more head, neural, and ligament 

injuries on natural grass, while there are more 

epidural, muscle trauma, and temperaturerelated injuries on synthetic turf (Refs. 3, 4).

•	 Economics – Synthetic turf’s higher initial cost 

is offset by reduced maintenance associated 

with water, fertilizer, pesticides, cutting, turf 

replacement, and manpower. In some cases, 

budget, knowledge, and the availability of labor 

may limit proper maintenance of grass fields.

•	 Availability – Traditional turf may not be used 

for play without sustaining expensive damage 

when it is wet, limiting use of these facilities. 

Conversely, synthetic turf drains rapidly, allowing 

use quickly after heavy downpours. In addition, 

synthetic grass turf can reportedly tolerate up 

to 3,000 hours of use per year, about four times 

more use than natural grass turf, allowing the 

fields to be used more heavily for different sports.

These factors have fueled its rapid growth. Some 

questions have also been raised about the synthetic 

turf system. The following is a brief discussion of 

major issues and the status or conclusions based on 

available data.
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•	 Elevated Turf Temperature – The pieces of black 

rubber and colored synthetic turf blades absorb 

light energy and become warmer than ambient 

temperatures. Limited data report surface 

temperatures of 49o C to 65o C (120o to 150o F) on 

sunny summer days with ambient temperatures 

of about 35o C (95 to 100o F). Other surfaces 

also tend to exceed ambient temperatures, 

even cement roadways and light-colored sand 

on beaches. The New York State Department of 

Environmental Conservation conducted a study 

in 2009 indicating that surface temperatures 

of synthetic turf are warmer than natural grass 

or sand, but that differences in wet bulb globe 

temperatures that more accurately reflect actual 

heat stress were similar, with minimal impact on 

athletes (Ref. 5). Customer reactions have ranged 

from no concern to limiting use during peak 

temperature times or using a water spray to cool 

the surface before use (Ref. 3).

•	 Metals Leaching – Tire rubber contains zinc, 

sulfur, and small quantities of other materials 

that are naturally in the environment at 

concentrations greater than can be leached by 

water flowing through rubber (above the water 

table). These metals are within the vulcanized 

rubber (rubber which has been chemically 

altered to increase elasticity and decrease 

temperature sensitivity) polymer matrix, but can 

be leached from the rubber surface by water. 

Multiple studies indicate that these metals do 

not represent an acute or chronic health or 

environmental hazard under conditions likely 

to be encountered on athletic fields based on 

established scientific evaluation criteria (Refs. 5 

through 11).

•	 Organic Chemical Emissions – Studies indicate 

that a range of organic compounds may be 

emitted onto or from the surface of ground 

rubber pieces. Detailed studies conducted 

in Europe concluded that these materials do 

not represent a significant hazard to players 

or spectators in outdoor sports arenas with 

synthetic sports turf (Refs 11 to 14). Maintaining 

a minimum air turnover rate within the normal 

building design range was suggested to 

limit exposure in indoor sports arenas. These 

studies were prompted by concerns raised in 

Europe in 2002. Athletic federations examined 

the data and decided that the surfaces with 

ground rubber were suitable for use by their 

athletes. The issue has been raised again in the 

northeastern United States. Additional reviews 

of available data have been prepared, generally 

reaching the same conclusions about safety and 

environmental concerns. A list of representative 

studies is provided in the reference section at 

the end of the ground rubber section (Refs. 15 

to 23). None of these studies indicates that the 

thousands of surfaces in the United States or 

Europe have caused health problems in athletes 

or spectators. Some cite the need for additional 

data, especially practical data from actual field 

installations. The U.S. State of New York issued 

its report in May 2009 with its structured 

field tests, confirming the acceptability of 

this material and surface (Ref. 5). California is 

currently planning structured field tests to 

further broaden the available database (Ref. 

24). 

Playground Safety Surfaces

Sand, wood chips, and small gravel are commonly 

used as cushioning materials around playground 

equipment, but each has limitations. Wood chips 

deteriorate with time, causing loss of cushioning 

and requiring frequent addition of more wood 

chips. Sand and gravel are limited in their ability 

to absorb impact. The development of scrap tire 

processing technologies created products suitable 

for use in three alternative types of playground 

cushioning surfaces that have been accepted in 

the United States. 

Description

The three playground cushioning alternatives 

involving ground rubber in different forms are: 

(1) loose fill, (2) pour-in-place, and (3) molded 

tiles. Loose fill, pictured in Exhibit 3-3, was the 

first playground safety material derived from 

Exhibit 3-3. Loose fill ground rubber installation 

Photo courtesy of American Rubber Technologies, Jacksonville, FL
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scrap tires. It is simply ground rubber about 1 cm 

(3/8 inch) in size with virtually all of the reinforcing 

wire removed. Some loose fill is made from fabricreinforced truck tires or off-road tires to be sure that 

no wire is present. It is spread under and around 

playground equipment. A 14-cm (6-inch)-thick 

layer generally provides protection for falls from 

critical heights of about 3 m (10 to 12 feet), about 

double the height for an equivalent thickness of 

traditional materials. The ground rubber loose fill is 

normally placed over a substrate that freely drains 

liquids with a wooden border to keep loose fill from 

spreading away from the playground area. Tires are 

black, but loose fill can also be colored before it is 

installed to improve the aesthetic appearance of the 

playground.

Pour-in-place installations at playgrounds, shown 

in Exhibit 3-4, use a polyurethane binder to bond 

ground rubber or buffings from tire retread 

operations into a protective surface mat 5 to 10 

cm (2 to 4 inches) thick. The ground rubber and 

polyurethane binder are commonly mixed on site 

in a portable cement mixer and then trowelled 

into place. A surface layer of colored ethylenepropylene-diene monomer (EPDM) rubber is 

generally bonded to the ground rubber base to 

provide distinctive colored surface patterns or 

pictures. Pour-in-place is normally installed over 

a hard surface such as asphalt to provide a stable 

foundation. The installation should be designed 

and tested to provide fall protection from heights 

associated with the various equipment at the 

playground. 

Ground rubber can also be molded into thick 

interlocking tiles specifically designed to provide 

protection from falls. The tiles, shown in Exhibit 

3-5, are typically 1/3 to 2/3 m (1 to 2 foot) squares 

and 5 to 10 cm (2 to 4 inches) thick and are 

commonly glued to a hard sub-base such as asphalt. 

Each tile is designed and manufactured to provide 

a durable surface that meets specific cushioning 

specifications. 

Current Market Status

All three of these ground rubber products for 

cushioning playgrounds have been broadly used, 

but no published market data define the specific 

quantities of ground rubber used annually for these 

installations. It is substantial, but not growing rapidly. 

Many states have encouraged use of these products 

through cost-sharing grants, but volumes have been 

limited outside of these special programs. California, 

Florida, Kentucky, and Illinois are among the states 

that have aggressively promoted this application. 

Loose fill is the least expensive to install. It has been 

widely used in Florida and Kentucky. The primary 

cost is the ground rubber itself, plus preparation of 

the base under the loose fill and the border around 

the perimeter of the area that will contain the ground 

rubber. Initial cost is generally more expensive than 

wood chips, but ground rubber does not degrade, 

so the annual replacement cost is lower. All loose 

playground cushioning products must be periodically 

re-leveled to maintain the desired thickness under 

and around equipment.

The total installed cost of pour-in-place and tiles are 

typically four to 10 times more than loose fill because 

of base preparation, the expense of binders, and 

labor for installation. Pour-in-place and tiles have 

been used extensively in California and Florida under 

state government grant programs that foster market 

development, but have seen limited use outside of 

these programs. 

Ground Rubber Requirements

A range of ground rubber piece sizes is used in 

each of these playground surfaces. Manufacturing 

appropriate sizes for loose fill is controlled by the 

Exhibit 3-4. Pour-in-Place Installation

Photo courtesy of Calgary, Canada, Parks and Recreation

Exhibit 3-5. Interlocking Tile Installation

Photo courtesy of Calgary, Canada, Parks and Recreation
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need to separate and remove virtually all reinforcing 

wire from the scrap tire to avoid puncture wounds or 

injury. It is normally 1⁄2 to 11⁄4 cm (1⁄4 to 1⁄2 inch) in size 

and is sometimes produced from fabric-reinforced 

truck tires or off-road farm tires that do not contain 

fine reinforcing wire to minimize potential residual 

wire in the product. Heavy bead wire around the rim 

of a tire is removed by debeading equipment before 

tires are processed or by magnets after processing. 

The material must be free of particles smaller than 20 

mesh to minimize dust generation and small particles 

that cling to skin and clothes like dirt. Residual fluff 

from reinforcing fabric in tires is sometimes left in the 

ground rubber; it may improve resiliency, but it may 

also decrease the flash point of the mixture and allow 

it to be ignited by vandals more readily. 

Pour-in-place and tiles generally use 3 to 10 mm 

(3/8 to 1/8 inch) ground rubber. In both cases, the 

fabric is removed to improve the efficiency and 

effectiveness of the binder, and the wire must be 

removed to minimize scrapes and cuts. A layer of 

colored synthetic rubber, known as EPDM (ethylene 

propylene diene Monomer rubber) or M-class rubber 

is commonly added to the ground rubber surface 

to add color and enhance surface aesthetics. Light 

colors can decrease light absorption and lower the 

surface temperature in warm weather.

Application Benefits and Issues

Durability – Rubber is flexible, resilient, and durable, 

properties that make it a good outdoor cushioning 

material. Some loose-fill playgrounds have been in 

place for more than 10 years with minimal need to 

add more ground rubber to replace material lost. 

The longevity of pour-in-place and tile surfaces is 

controlled by the effectiveness of the installation, 

binder, foundation, and usage, but manufacturers 

typically project a duration of more than 5 years.

Accessibility – Accessibility of equipment by children 

in wheelchairs or on crutches can be an important 

consideration. Loose fill’s excellent cushioning 

characteristics also make it less stable under point 

loads such as wheel chairs, but some products have 

reportedly passed tests that demonstrate accessibility. 

Pour-in-place and tiles have excellent accessibility, 

so some playgrounds use them for access pathways 

and around some of each equipment type to assure 

access. Loose fill is used in other areas to control cost. 

Flammability – Tire rubber has a flash point of more 

than 290° Celsius (550° Fahrenheit), higher than dry 

wood chips, and so is not readily ignitable. Fires have 

occurred in loose-fill installations, but there were no 

injuries or environmental damage other than the 

initial smoke. The California Department of Resources 

Recycling and Recovery (CalRecycle) documented a 

detailed examination of one playground fire site and 

found no residual environmental damage (Ref. 26). 

Application Public Health Benefits and Issues

Latex Sensitivity – A small percentage of people are 

sensitive to the latex present in some types of rubber. 

CalRecycle tested for latex sensitivity in styrenebutadiene rubber (SBR) derived from scrap tires as 

part of its comprehensive review of ground rubber 

playground surfacing. The testing showed no 

sensitivity using established testing procedures on 

SBR and EPDM ground rubber, and no documented 

cases were found in a literature search (Ref. 22).

Toxicity – Toxicity and environmental questions 

associated with ground rubber have been 

raised for playground applications as well as for 

synthetic turf, with the same general conclusions 

as previously discussed. CalRecycle’s detailed 

report addresses many of these concerns. It (1) 

identified no issues that would preclude using 

the superior cushioning characteristics of ground 

rubber on playground safety surfaces and (2) 

fully recognized the benefits of reducing injuries 

through use of ground rubber. The report is titled 

“Evaluation of Health Effects of Recycled Waste 

Tires in Playground and Track Products” (Ref 22) 

and is available on the CalRecycle web site at 

www.calrecycle.ca.gov.

Impact Cushioning – The primary objective 

of playground safety surfacing is reducing the 

impact of falls from equipment, and all three 

of these alternatives can serve this function as 

well as, or better than, natural materials when 

properly installed and maintained (Ref. 24). The 

U.S. Consumer Product Safety Commission has 

prepared a guide that provides detailed data and 

discussion of safety parameters for playgrounds, 

including surfaces. It is available on the web site at 

www.cpsc.gov as Publication 325, titled “Handbook 

for Public Playground Safety.”

MOLDED AND EXTRUDED PRODUCTS

Molded or extruded products can be created when 

heated rubber is pressed into a mold or through a 

die cast to shape it into a new product. This market 

is very versatile and can create a wide variety of 

products ranging from pet toys, car bumpers, gaskets, 

and garden hoses to complex components for 

medical and electrical equipment. 
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Chapter 3: Ground Rubber Scrap Tires: Handbook on Recycling Applications and

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Molded and extruded products are the secondlargest application for ground rubber from scrap 

tires based on market data compiled by the Rubber 

Manufacturers Association (Ref. 1). These products 

represented 36 percent of ground rubber usage in the 

United States in 2007. This market is continuing to 

grow. It is a diverse market in terms of products and 

manufacturing technology and may have significant 

potential applicability in Mexico. The objective of 

this summary is to identify major product categories 

and technologies, and then provide references for 

additional depth.

Description

Molded products have been made from buffing 

dust (rubber particles removed from a tire carcass 

during retreading) for many years, but the range 

of products and the size of the markets have 

expanded significantly in the past 5 to 10 years. 

Three primary technologies are used to produce 

products that use ground rubber by itself or in 

blends with other materials. The following is a brief 

discussion of these technologies.

Molded Products

Many initial products were relatively small molded 

parts such as wheels for trash cans. There are many 

variations in molding technology, all using a similar 

basic process. A primary raw material or mixture is 

pretreated to allow it to flow into a mold where the 

material is cured, cooled, and released from the mold 

to yield a solid designed shape that meets defined 

specifications. Pretreatment can involve heat, mixing, 

and additives to create a semi-viscous homogeneous 

raw material. Once it has been introduced into the 

mold, temperature, pressure, and reaction time 

allow the material to solidify. There are also broad 

variations in degree of automation, balancing capital 

and labor costs for a specific operating environment. 

This basic technology has been fully demonstrated 

with many polymers and rubber materials, including 

mixtures with ground rubber. Each component of 

the process requires experimentation to optimize 

efficiency and product quality. This technology 

can be labor intensive in its basic form, making 

Mexico’s labor economics potentially attractive to 

the manufacturing of these products as well as to 

increasing employment. 

One example and potentially viable market that uses 

this process is the production of traffic cones (also 

known as road cones, safety cones, or pylons). The 

cone base is produced through compression molding 

of ground rubber obtained from scrap tires. The 

cone portion is made from recovered plastic material. 

The recycled materials content can range from 50 to 

100 percent, depending on the production process, 

making these products environmental friendly. More 

information on the use of ground rubber in traffic 

cones can be found on line at www.epa.gov/epawaste/

conserve/tools/cpg/products/cones.htm.

Bound Systems

Bound or bonded rubber products generally refer 

to use of polyurethanes, sulfur, latex, or other 

ingredients to bond particulate materials into a 

desired product. This is sometimes done using 

pressure and temperature to increase density or 

optimize efficiency. This technology was initially 

used on large, low-volume products such as railroad 

crossing fillers and speed bumps. With improved 

binders and product creativity, a broad range of 

higher-volume products have been produced and 

marketed successfully. The initially simple welcome 

mats using bound ground rubber evolved into 

attractively designed mats with mass market appeal, 

becoming a major consumer of ground rubber. Other 

mats gained acceptance in agricultural, recreational, 

and building applications. For instance, mats placed 

in livestock areas have been shown to increase milk 

production in dairy cattle and enhance weight gain in 

beef cattle. This provides an economic driving force 

for this large, established market segment in North 

America.

The playground safety tile discussed in the preceding 

section is an example of a bound product. A newer 

Sample of molded rubber traffic cone

Photo courtesy of Candy Lee
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developing market uses thin sheets of bound ground 

rubber as carpet cushioning and sound deadening 

in residential apartments and houses. This product is 

sometimes made by peeling a thin layer off of a large 

bound rubber cylinder; efficiently producing a long 

roll of 1⁄2 to 1 cm (1⁄4 to 1⁄2 inch) thick rubber matting 

that is easily transported and installed. It can also be 

manufactured as sized sheets. 

Many binders have been used, but polyurethanes 

and sulfur are the most common. Sulfur is considered 

more durable and suitable for ultraviolet (UV) 

exposure in outdoor applications. Some types of 

polyurethane are able to tolerate UV, and coloring can 

be used in these products to shield the polyurethane 

binder from UV exposure.

Hundreds of products have been made using 

bound ground rubber, representing both small 

and large markets. Some products and processes 

are simple while others have necessarily become 

more sophisticated to meet specifications or to 

achieve the efficiency required to compete in the 

marketplace. A good understanding of existing 

products, performance requirements, processing 

technology, and economics is critical to developing 

these applications successfully. It typically takes 

a committed effort over a period of time to be 

successful.

Extrusion

Long items such as hoses, weather stripping, tubes, 

molding, and belting are commonly made by 

extrusion processes. There are also many variations of 

this technology, but it normally involves using a screw 

system to mix, heat, and force a raw material through 

a die to produce a continuous shape. This process 

is sensitive to multiple parameters and requires fine 

mesh ground rubber (30 to 200 mesh). Any residual 

wire or fiber can accelerate wear or damage extrusion 

heads and equipment. Extrusion may have greater 

future applicability for using mixtures of ground 

rubber and plastics to produce high-volume products 

such as synthetic wood, shingles and other structural 

materials. 

Ground Rubber Requirements

Ground rubber specifications for this market segment 

depend on the process, product, and economics. 

Desired product characteristics control the size 

requirements for ground rubber pieces used in 

these applications. Larger piece size reduces binder 

requirements and retains the characteristics of rubber, 

but the resulting product has less bonding strength 

and coarser surface texture. Playground safety tiles 

are an example of an appropriate use of about 0.5 

cm (1⁄4 inch) ground rubber. Finer particles (10 to 

40 mesh) require more binder, with its associated 

strength, and yield a smoother surface that can 

approach virgin materials. Wheels and vehicle mud 

flaps are two examples of products that require such 

fine particles. 

Economics also play a role in rubber selection. The 

cost of ground rubber generally increases with 

decreasing piece size, and binders are generally 

much more expensive than the ground rubber. As 

a result, products made with finer rubber and more 

binder generally are more expensive. Ultimately, 

the product must compete cost-effectively in the 

market to be successful.

Application Benefits and Issues

Low-Cost Raw Material

Ground rubber can be a low-cost raw material 

with many of the intrinsic performance properties 

of rubber. The creativity and technology applied 

to its use have increased market diversity and 

volumes. This trend is expected to continue as 

costs of virgin raw material escalate.

Displacement Challenges

Making any new product can involve substantial 

investment in processing technology, equipment, 

optimization, product testing, distribution, 

and marketing. All require time and resources 

that are often underestimated. Incorporating 

ground rubber into an existing formulation can 

pose similar challenges, especially in process 

optimization and product testing.

Mixtures

Rubber generally functions as filler in mixtures with 

plastics. Thermoset rubber and thermoplastics 

do not naturally bond, resulting in significant 

changes in the performance characteristics of 

plastics when rubber is added. Impact resistance 

normally increases, but other critical properties 

such as tensile strength and elongation decrease 

significantly, thereby decreasing the strength of the 

resulting product. Broader applicability of these 

mixtures hinges on identification of products where 

impact resistance dominates other performance 

requirements or on development of economically 

viable rubber surface modification technology that 

will allow the materials to bond. Extensive research 

has been devoted to this subject with some success 

in reducing property deterioration, but the resulting 

products have rarely competed successfully with 

alternative virgin materials. However, the increasing 
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cost of hydrocarbon-based polymers and virgin 

rubber may provide additional incentive to further 

develop this technology or for manufacturers to 

tolerate moderately reduced performance. 

RUBBER MODIFIED ASPHALT

Rubber modified asphalt is the product of mixing 

crumb rubber from scrap tires or other sources with 

asphalt. This can be done at varying rubber to asphalt 

ratios dependent on its intended use. Initial rubber 

modified asphalt technology was developed more 

than 30 years ago, has been actively promoted for 

at least the past 20 years, and has continued to 

evolve. The McDonald patents have expired, and 

this technology is now commonly referred to as 

the Arizona Process because of its extensive use 

within Arizona. Variations have been developed 

in an effort to address perceived obstacles or 

improve performance. In each case, rubber is 

mixed with the asphalt binder. The asphalt binder 

is then mixed with the aggregate and spread 

on the roadway to form asphalt pavement. This 

technique is commonly known generically as the 

wet process because rubber is mixed with the 

asphalt binder first. 

Description of Technologies

The following is a brief description of the three 

major rubber modified asphalt technologies:

Arizona Process

The Arizona process involves mixing and reacting 

rubber with asphalt binder in specialized 

equipment at the paving site. Ground rubber 

normally represents about 20 percent of the 

asphalt binder mix, significantly increasing the 

viscosity of the binder. Greater viscosity allows 

a higher concentration of binder to be used 

in the asphalt mix, resulting in a stronger and 

more durable pavement. Use of rubber, more 

asphalt binder, and specialized on-site blending 

equipment increases unit cost/ton of asphalt 25 to 

100 percent above traditional asphalt, depending 

on location, job size, and other job-specific criteria. 

In some cases, increased pavement strength has 

allowed thinner rubber modified asphalt overlays to 

demonstrate life comparable to thicker traditional 

asphalt, so that the installed cost of rubber modified 

asphalt is comparable. 

Terminal Blending

Terminal blending involves blending rubber into the 

asphalt binder in a mixing tank at the asphalt supply 

terminal, then transporting it to the job site, thereby 

reducing the need for specialized equipment at the 

site. The terminal blending mix must be continuously 

mixed to keep the suspended rubber from settling 

out prior to transport. Rubber usage levels are 

specified to meet design performance characteristics 

for the pavement. This technology has been used for 

15 years in Florida with a good performance history. 

Florida was the only state to specify rubber modified 

asphalt for friction course replacement on most statemaintained, high-traffic roads, including interstate 

highways. The technology is gradually being used 

more widely in other states such as California because 

of its lower cost.

Rubber/Polymer Blends

Styrene-butadiene-styrene (SBS) block copolymers 

are also used as additives in asphalt to improve 

performance. However, proponents believe that 

addition of a combination of both the SBS block 

copolymer and rubber to the asphalt enhances the 

performance more than either material can when 

they are added separately. This technology has 

been broadly applied in Texas and other U.S. states 

by using variations of the compounds, depending 

on the geographic area of application. The Florida 

Department of Transportation (DOT) is conducting a 

comprehensive evaluation of several polymer/rubber 

technologies compared with traditional asphalt. 

The technology uses a low percentage of rubber to 

partially displace normal polymer addition levels. This 

technology is the newest, but it is rapidly developing 

a substantial experience and testing base.

The availability of rubber, polymer, and rubber/

polymer blend technology is also playing a role in 

development of pavement design alternatives that 

can reduce road noise levels and improve the safety 

of highways. Noise reduction and increased safety are 

accomplished through use of open-graded friction 

course (OGFC) pavement using large, uniformly 

graded aggregate. Rainwater flows through the 

resulting top layer of pavement (the friction coarse) 

and out to the sides of the roadway. This reduces 

hydroplaning and enhances driver visibility through 

a reduction in water spray from the vehicle tires. The 

open structure also creates an acoustic surface that 

absorbs and deflects some sound and reduces road 

noise for nearby residents. Experiments are under 

way to determine if the noise reduction levels will 

allow long-term use of this pavement as an alternative 

to expensive and unattractive noise barriers along 

highways through populated areas. Arizona and 

California are actively using this material, and other 

states such as Texas are using OGFC for safety reasons 

on historically dangerous roads. Enhanced binders 
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play a critical role in allowing OGFC to maintain its 

long-term integrity, and rubber contributes to sound 

reduction.

Current Market Status

Rubber modified asphalt is the third-largest 

application for ground rubber in the United States. It 

represents 9 percent of the ground rubber market or 

less than 2 percent of the annual scrap tire generation 

in 2007, according to the Rubber Manufacturers 

Association (RMA) (Ref. 1). More than 90 percent 

of the rubber modified asphalt is currently used in 

Arizona, Florida, Texas, California, and South Carolina. 

Many other states have conducted trials or trial 

programs, but their use of rubber modified asphalt 

remains small. In addition, the Provinces of Alberta 

and Ontario in Canada have conducted thorough 

test programs. Still, total use of ground rubber in this 

application has not grown significantly in the past 5 

to 10 years. Reduced paving and cost consciousness 

caused by transportation departments’ budget 

constraints have contributed to limited growth.

Ground Rubber Requirements

Each state in the United States has established its 

own ground rubber specifications with variations 

for alternative applications. The Arizona process 

typically uses 16-30 mesh ground rubber with low 

limits for residual wire and fiber. Terminal blending 

in Florida initially used fine-mesh, such as minus 

80 mesh (the minus implies that it is finer than 80 

mesh since material has passed through a 80 mesh 

screen) ground rubber, but found that minus 40 mesh 

performed well with lower cost and better availability. 

Polymer/rubber blends vary widely, with some 

technologies pre-treating the rubber to enhance its 

reactivity in the asphalt.

Application Benefits and Issues

Performance 

Roads using the Arizona and terminal blend 

processes have been documented to last longer 

than traditional asphalt, sometimes dramatically 

longer, but this performance has not been universal. 

Poor performance has been attributed to improper 

installation, weather conditions, bed preparation, 

and aggregate grading. Florida found that rubber 

modified asphalt performed well, but that polymers 

out-performed terminal-blended rubber modified 

asphalt for some high-traffic applications. This 

finding prompted interim modification of 

specifications to allow use of polymers and 

initiated Florida’s previously referenced research 

into polymer/rubber blends. Tests in Alberta 

found variations in performance, some probably 

attributable to the initial learning curve.

Cost 

 The installed cost of an equivalent thickness 

of rubber modified asphalt is generally 10 to 

100 percent higher than unmodified asphalt, 

as previously discussed. Since transportation 

departments’ budgets are fixed, higher cost forces 

less paving and can cause short-term problems 

even if it has long-term benefits. Use of thinner 

rubber modified asphalt lifts (layers) can turn 

cost into an advantage where applicable and 

accepted.

Cost Justification 

As the public becomes more aware of the 

safety and noise advantages of OGFC, the cost 

comparison should appropriately be broadened 

to include other avoided costs such as accidents 

and sound barriers. In that case, the comparison 

is not with traditional asphalt, but instead is with 

alternative OGFC mixes, and rubber modified 

asphalt is a proven material in these applications.

Horse arena using ground rubber surfacing 

Photo courtesy of American Rubber Technologies, Jacksonville, Florida

Ground rubber used to create mulch

Photo courtesy of American Rubber Technologies, Jacksonville, FL
32

Chapter 3: Ground Rubber Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

Ground Rubber Quality

The quality of the ground rubber is a critical 

performance factor in rubber modified asphalt. 

Ground rubber processors must recognize 

and consistently meet applicable product 

specifications. Failure to do so places the 

pavement at risk and alienates transportation 

departments and their installation contractors. 

OTHER MARKETS

There are many smaller markets for ground 

rubber. Some are variations of the major markets 

discussed above, while others are unique niche 

products, and a few offer significant potential 

for growth. The following is a brief discussion of 

some of these products:

Horse Arena Cushioning

A variation of loose fill used as playground safety 

cushioning, ground rubber serves a similar 

function in horse arenas. It provides similar 

protection for horses and riders during practices 

and exhibitions. It also reportedly enhances 

footing and reduces stress on the horse’s legs 

and joints. The material must meet defined 

specifications to balance sure footing with impact 

safety. This small, useful, and stable market may 

offer significant market potential to Mexico. 

Animal Mattresses 

Coarse ground rubber is used as filler in fabric 

mattresses that provide an alternative to the molded 

and bonded products discussed earlier. They are used 

primarily in the dairy industry to reduce leg injury, 

enhance comfort, and provide protection for utters 

of milking cows, which can increase milk production. 

Research has shown that rubber-filled mattresses 

last longer, as they do not compress as quickly and 

they are preferred in extreme temperatures (Ref. 

26). It uses less than 3 percent of the current ground 

rubber stock and is a market that shows growth 

potential, according to the U.S. Rubber Manufacturers 

Association (Ref. 1).

Colored Mulch

Wood mulch is commonly spread around plants 

and flower beds to retain moisture, control weeds, 

and enhance beauty of the beds. However, mulch 

decomposes, harbors insects, and requires frequent 

replacement. Initial experimentation with black tire 

chips found that they controlled weeds much like 

wood chips and stayed in place, but the black color 

absorbed heat and had limited aesthetic appeal. 

Extensive experimentation led to relatively simple 

methods to color chips with paint that adheres and 

resists fading to assure warranted performance for 5 

years or more.

Today’s colored mulch is 1 - 2.5 cm (3/8 to 1 inch) 

chips made from scrap tires with 99 percent of the 

reinforcing wire removed. It is manufactured in many 

pleasing colors to simulate wood chips or to provide 

coordinating and contrasting colors. It has been 

shown to control weeds, resist mold, retain moisture, 

and require infrequent addition. As added benefits, 

it does not harbor insects or attract neighborhood 

animals. 

Some issues have been raised about the use of 

colored mulch, as discussed below:

Flammability

Limited tests have shown that colored mulch has 

an ignition temperature above 290° Celsius (550° 

Fahrenheit), so flammability is comparable to dry 

wood chips.

Temperature

Black ground rubber pieces absorb light and can heat 

up. Colored mulch does not absorb as much energy 

thereby reducing the temperature increase. 

Zinc Leaching

Tire rubber contains about 1.5 percent zinc as a 

vulcanization accelerator within the rubber polymer 

matrix. Water can gradually leach small amounts of 

zinc from the chip into the underlying soil. Traces 

of zinc serve as a micronutrient for many species, 

but excessive quantities can have a negative impact 

on some plants and grasses. Leaching is slow and 

controlled with water flowing through chips on 

the surface of beds, but it could be accelerated by 

continuous submersion in water or soil. Therefore, 

colored mulch should be kept on the bed surface and 

not mixed with soil. Coloring the mulch limits chip 

Ground rubber mulch 

Photo courtesy of American Rubber Technologies, Jacksonville, FL
33

Chapter 3: Ground Rubber Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

surface exposure to moisture and further reduces 

possible leaching. 

Rubber mulch was initially sold in small quantities 

through nurseries, landscapers, and specialty shops. 

However, it is becoming an established product with 

increasing representation in major high-volume 

retailers throughout the United States. If current 

growth rates continue, colored rubber mulch could 

become a large, high-value market for small scrap tire 

chips.

SUMMARY

Ground rubber products embody the creativity and 

expertise that have been developed to constructively 

make use of scrap tire resources. Although it may 

be desirable to use all scrap tires in these and similar 

applications, it has taken many years to reach 17 

percent of annual scrap tire generation. These 

products can be an important long-term component 

of scrap tire use, while initial market development 

efforts focus on energy and civil engineering 

applications to maximize short-term use of this 

resource.

REFERENCES

1. Rubber Manufacturers Association. 2009. Scrap 

Tire Markets in the United States. 9th Biennial 

Report. May.

2. Dick, R.W. 2004. Injury Surveillance SystemFootball 2004-04. NCAA Research.

3. Meyers, M.C. and B.S. Barnhill. 2004., Incidence, 

causes and severity of high school football 

injuries on FieldTurf versus natural grass. Am J 

Sports Medicine, 32(7).

4. McNitt, A.S. and Petunak, D . Evaluation of 

Playing Surface Characteristics of Various In-filled 

Systems. Penn State University (http://cropsoil.

psu.edu/menitt/Infill.cfm)

5. Lim, L and Walker, R. 2009. An Assessment 

of Chemical Leaching, Releases to Air and 

Temperature at Crumb-rubber Infilled Synthetic 

Turf Fields. New York State Department of 

Environmental Conservation and New York State 

Department of Health. May.

6. Verschoor, A.J. 2007. Leaching of zinc from 

rubber infill on artificial turf (football pitches). 

RIVM: Bilthoven, the Netherlands.

7. Downs, L., and others. 1996. Water quality 

effects of using tire chips below the groundwater 

table. In: Department of Civil and Environmental 

Engineering, University of Maine: Orono, Maine.

8. Humphrey, D.N. and E.K. Lynn. 2000. Five Year 

Study of the Water Quality Effects of Tire Shreds 

Placed Above the Water Table. Transportation 

Research Board: Washington, DC.

9. Sullivan, J.P. 2006. An Assessment of 

Environmental Toxicity and Potential 

Contamination from Artificial Turf using 

Shredded or Crumb Rubber. 

10. Kallqvist, T. 2005. Environmental risk 

assessment of artificial turf systems. 

Norwegian Institute for Water Research: Oslo.

11. Johns, D.M. and Goodlin, T. 2008. Evaluation 

of Potential Environmental Risks Associated 

with Installing Synthetic Turf Fields on 

Bainbridge Island. Seattle, Washington: 

Windward Environmental LLC.

12. Norwegian Institute of Public Health and the 

Radium Hospital. 2006. Artificial turf pitchesan assessment of the health risks for football 

players. Oslo, Norway.

13. Nilsson, N.H., A,Feilberg, and K. Pommer. 

2005. Emissions and evaluation of health 

effects of PAHs and aromatic mines from 

tyres. Danish Ministry of the Environment.

14. The Swedish Chemicals Inspectorate 

(Kemi). 2006. Synthetic turf from a 

chemical perspective – a status report. 

KEMIKALIENIMSPEKTIONEN Sundbyberg. 

15. Hoffman, K., and others. 2000. The German 

environmental survey 1990/92 (GerESII): 

Sources of personal exposure to volatile 

organic compounds. Journal of Exposure 

Analysis and Environmental Epidemiology. 10: 

p. 115-125.

16. Birkholz, D.A., K.L. Benton and T.L. Guidotti. 

2003. Toxicological evaluation for the hazard 

assessment of tire crumb for use in public 

playgrounds. J Air Waste Management Assoc, 

53(7).

17. Ledoux, T. 2007. Preliminary Assessment of 

the Toxicity from Exposure to Crumb Rubber: 

its use in Playgrounds and Artificial Turf Playing 

Fields. New Jersey Department of Environmental 

Protection, Division of Science, Research and 

Technology: Trenton, New Jersey.
34

Chapter 3: Ground Rubber Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

18. Johns, D.M. 2008. Initial evaluation of potential 

human health risks associated with playing 

on synthetic turf fields on Bainbridge Island. 

Seattle, Washington: Windward Environmental 

LLC.

19. Brown, D.R. 2007. Artificial Turf – Exposures 

to Ground-Up Rubber Tires – Athletic Fields – 

Playgrounds – Gardening Mulch. N. Alderman 

and S. Addiss, Editors, Environment & Human 

Health, Inc. North Haven, Connecticut, p. 1-40.

20. New York City Department of Health and Mental 

Hygiene. 2008. A Review of the Potential 

Health and Safety Risks from synthetic Turf 

Fields Containing Crumb Rubber Infill. Windsor, 

Connecticut: TRC.

21. Rubber Manufacturers Association. 2008. 

Review of the Human Health and Ecological 

Safety of Exposure to Recycled Tire Rubber 

found at Playgrounds and Synthetic Turf Fields. 

Pittsburgh, Pennsylvania: Chem Risk, Inc.

22. California Integrated Waste Management 

Board. 2007. Evaluation of Health Effects of 

Recycled Waste Tires in Playground and Track 

Products. Sacramento, California.

23. New York State Department of Environmental 

Conservation. 2008. A Study to Assess the 

Environmental Impacts from the Use of Crumb 

Rubber as Infill Material in Synthetic Turf Fields. 

June 17. 

24. California Integrated Waste Management 

Board. 2008. Draft Scope of Work: Evaluation 

of the safety of artificial turf fields containing 

crumb rubber from recycled tires. : 

Available from: www.ciwmb.ca.gov/agendas/

mtgdocs/2008/04/00023252.doc. 

25. Amme, R.C., and others. 2003. Scrap tires 

in full swing: a recent study demonstrates the 

benefits of playground surfaces covered with 

recycled crumb rubber. Resource Recycling.

26. California Integrated Waste Management Board. 

2004. Construction Completion Report for the 

Yulupa Elementary School Tire Chip Fire.

27. Fulwider, W., and others. 2004. Use of Impact 

Testing to Predict Softness, Cow Preference, and 

Hardening over Time of Stall Bases. Journal of 

Dairy Science. 87: 3080-3088.
35

Chapter 4: Energy Utilization Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

CHAPTER 4

Energy Utilization

Scrap tires are a resource. The cornerstone of 

an effective scrap tire management program is 

developing diverse applications, or purposes for 

which to apply this resource, preferably ones that (1) 

can be developed reasonably quickly; (2) use large 

quantities; (3) are technically and environmentally 

sound; and (4) are economically feasible and 

sustainable. The largest application in the United 

States, Europe, and Japan, among others, is using 

scrap tires as a supplemental energy resource. 

Scrap tires have been used for energy in Japan, 

Europe, and the United States since the 1970s. 

Paper manufacturing mills began using tire-derived 

fuel (TDF) in the United States in the late 1970s. 

The experience base has broadened significantly 

during the last 10 to 15 years as tires have become 

recognized as a viable alternative fuel in appropriate 

combustion processes. Once a tire is in a scrap tire 

pile, its uses are limited but it is still a viable option for 

energy utilization. Applications include cement kilns, 

industrial boilers, utilities, and dedicated electrical 

generation facilities. In 2007, 123 permitted facilities 

used 155 million waste tires as fuel in the United 

States, according to a market analysis conducted by 

the U.S. Rubber Manufacturer’s Association (RMA) 

(Ref. 1). This volume represents almost 2.3 million 

metric tons (2.5 million U.S. tons) or 54 percent of 

scrap tire generation. 

The following sections discuss the energy and 

chemical characteristics of tires, as well as historical 

experience in major energy applications. The 

objective is to assist governments and industries 

in evaluating and developing these uses as part of 

evolving tire management programs in Mexico and 

the United States.

CHEMICAL CHARACTERISTICS OF 

SCRAP TIRES

The chemical characteristics of any energy resource 

affect its technical and environmental performance. 

Tires are a hydrocarbon-based material derived 

from oil and natural gas. Some inorganic materials 

are added to enhance vulcanization reactions or 

performance properties, such as flexibility and 

resistance to UV light. Tires have a heat content of 

14,000 to 15,500 British thermal units per pound (Btu/

pound) (7,800 to 8,600 kilocalories per kilogram [kcal/

kg]), depending on the type of tire and the amount 

of reinforcing wire that has been removed. By 

comparison, another solid fuel commonly displaced 

by use of tires as an energy resource is coal that 

typically contains 10,000 to 13,000 Btu/pound (5,550 

to 7,200 kcal/kg). 

Tires can be used whole in some applications, such 

as cement kilns. Others require tires to be shredded 

into smaller chips called TDF, with reinforcing bead 

and cord wire removed if necessary. Regardless of 

particle size, tires remain a solid fuel. Applicable 

systems must be able to receive and combust solid 

fuel to be a candidate for use of TDF. The energy 

from TDF can replace higher-cost oil and gas in 

some cases where oil, gas, and solid fuels are cofired in the same furnace. 

The composition of tires and coal vary, depending 

on type and source. However, Table 4-1 provides 

representative proximate and ultimate analysis 

of TDF with about 90 percent of the reinforcing 

wire removed and of a bituminous coal used to 

generate steam. Proximate analysis defines basic 

combustion characteristics. Ultimate analysis 

defines elemental composition.

 A comparison of the proximate analysis indicates 

that tires offer efficiency advantages versus coal. 

For instance, tires generally have lower moisture 

content than coal. Since energy required to heat 

and vaporize water is generally non-recoverable 

in the energy conversion process, lower moisture 

content can translate into higher combustion 

efficiency. TDF is 1 to 3 percent more efficient than 

the coals cited in Table 4-1 because of its lower 

moisture content. The lower ash content of TDF 

(without wire) offers a similar advantage versus coal 

and can decrease ash disposal costs. A tire’s higher 

volatile-to-fixed carbon ratio enhances its ability to 

combust rapidly and completely. TDF’s advantages 

become commanding when compared with some 

of the high-ash, low-Btu coal and lignite. Based on 

proximate analysis, tires compare favorably with coal 

as an energy source.

Based on ultimate analysis, tires offer some additional 

advantages and disadvantages. When compared with 

many Eastern U.S. coals, TDF’s lower sulfur content 

(especially in terms of pounds per million Btu) offers 
36

Chapter 4: Energy Utilization Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

the potential advantage of decreasing emissions 

of sulfur oxide gas compounds referred to as SOx. 

However, the sulfur content of many Western U.S. 

coals is lower, so sulfur oxides must be controlled 

within these systems to prevent an increase with 

TDF. 

Combustion systems burn less of a high-energy fuel 

to obtain the same energy, so expressing the ultimate 

analysis as pounds per unit of energy such as million 

Btu identifies some other important environmental 

factors. Combustion of TDF generates less carbon 

per million Btu than either coal cited in Table 4-1. 

Since carbon converts to the greenhouse gas carbon 

dioxide (CO2

) during combustion, TDF reduces 

emissions of this greenhouse gas compared with 

these coals. TDF also has a higher hydrogen content. 

When hydrogen combines with oxygen during 

combustion, it releases energy and forms water (H2

O) 

with no greenhouse gas, so energy released from 

hydrogen combustion also decreases formation of 

greenhouse gas compared with carbon. Therefore, 

TDF’s lower carbon and higher hydrogen content 

on an energy basis results in lower greenhouse gas 

generation. In addition, TDF’s lower nitrogen content 

can marginally decrease emissions of nitrogen oxide 

compounds called NOx. 

The chlorine content of tires is higher than some 

coals and comparable to other coals. In addition, 

the chlorine content in tires has been significantly 

reduced in many newer tires, as the chlorinated butyl 

inner liner has been replaced by alternative materials.

Table 4-1 Comparative Chemical Characteristics

CHARACTERISTIC BITUMINOUS COAL 

-NORTHEASTERN U.S.

TDF (90+% WIRE 

REMOVED)

SUBBITUMINOUS COAL - 

WESTERN U.S.

MOISTURE 

(% AS RECEIVED) 10.43 0.62 24.68

HEATING VALUE (BTU/

POUND, AS RECEIVED) 10,641 15,404 9,287

PROXIMATE ANALYSIS (%, DRY BASIS)

ASH 16.16 4.81 6.37

VOLATILE CARBON 38.14 67.06 44.43

FIXED CARBON 45.70 28.13 49.20

TOTAL 100.00 100.00 100.00

ULTIMATE ANALYSIS (%, DRY BASIS)

CARBON 65.49 83.79 70.73

HYDROGEN 4.56 7.13 4.85

NITROGEN 1.11 0.24 0.84

SULFUR 4.52 1.84 0.41

ASH 16.16 4.81 6.37

OXYGEN (by difference) 8.16 2.18 16.80

TOTAL 100.00 100.00 100.00

ULTIMATE ANALYSIS EXPRESSED AS POUNDS/MILLION BTU

CARBON 55.13 54.05 57.36

HYDROGEN 3.84 4.60 3.93

NITROGEN 0.93 0.16 0.68

SULFUR 3.81 1.19 0.33

ASH 13.61 3.12 5.17

OXYGEN (by difference) 6.87 1.42 13.62

SUBTOTAL 84.19 64.54 81.09

MOISTURE 9.80 0.40 24.68

TOTAL 93.99 64.94 105.77
37

Chapter 4: Energy Utilization Scrap Tires:

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Elemental ash analysis provided in Table 4-2 indicates 

that tires generally contain metals at concentrations 

comparable to, or lower than, coal, with one notable 

exception. Zinc is added to tires as part of the rubber 

vulcanization process at levels approaching 1.0 to 

1.5 percent by weight. Therefore, zinc levels in tires 

are much higher than in coal. Applications that 

use tires as an energy resource must therefore be 

able to control zinc emissions to avoid a negative 

environmental impact. Common air pollution control 

equipment such as electrostatic precipitators and 

baghouses effectively control zinc oxide emissions 

from TDF combustion. 

 From a chemical standpoint, tires offer both 

environmental advantages and disadvantages 

versus coal. Therefore, tires provide a valuable and 

environmentally friendly energy resource when used 

in applications that draw on their advantages and 

properly control their disadvantages.

Table 4-2 Elemental Metals Analysis

ELEMENT (OXIDE) BITUMINOUS COAL 

-NORTHEASTERN U.S. TDF 90% (WIRE FREE) SUBBITUMINOUS COAL WESTERN U.S.

MAJOR OXIDES, AS % OF ASH

Aluminum (Al2

O3) 19.10 <0.01 18.10

Calcium (CaO) 5.18 0.38 13.50

Iron (Fe2

O3) 20.40 0.32 4.90

Magnesium (MgO) 0.82 <0.01 4.52

Phosphorous (P2

O5) 0.17 <0.01 0.36

Potassium (K2

O) 1.87 <0.01 1.01

Titanium (TiO2

) 0.89 <0.01 1.20

Silicon (SiO2

) 49.20 0.52 36.20

Sodium (Na2

O) 0.71 <0.01 5.55

Sulfur (SO3

) 1.60 13.40

TRACE ELEMENTS, PARTS PER MILLION WITHIN COAL OR TDF

Silver 0.02 0.02

Arsenic 4 1

Barium 43 ND 694

Beryllium 1.3 0.2

Cadmium 0.02 0.0006 0.02

Chlorine 1200 0.149 900

Chromium 21 0.0097 5

Copper 10 13

Mercury 0.05 0.04

Manganese 62 <.01 18

Nickel 14 1

Lead 15 0.0065 4

Rubidium 15 4

Selenium 1 1

Silver 0.02 0.02

Strontium 41 <0.1 348

Vanadium 3 15

Zinc 97 1.52 8

Zirconium 26 22
38

Chapter 4: Energy Utilization Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

CEMENT KILNS

Scrap tires have been used as a supplemental 

fuel in cement kilns in Europe and Japan since the 

1970s. It also currently represents one of the largest 

applications in North America. Only one cement 

facility in the United States (then called Calavaras 

Cement in California) consumed waste tires 20 

years ago. In 2007, 43 cement facilities used either 

shredded or whole tires as a supplemental energy 

source in the United States, according to the U.S. RMA 

(Ref. 1). These facilities consumed nearly 607,000 

metric tons of TDF, representing about 44 million 

scrap tires. Others are conducting performance tests 

targeted at future use. Sixteen cement companies 

own these facilities, including the largest North 

American, Latin American, and global cement 

producers. Broad corporate experience enhances 

transfer in this technology for additional facilities and 

accelerates internal evaluation and implementation. 

Basic Process

Cement manufacturing technology has evolved, but 

the basic process has changed little. Major processing 

steps include the following:

•	 Raw material preparation: Major raw materials 

are crushed and blended in proper proportions, 

including limestone (CaCO3

), shale or clay (Al2O3

and other compounds), sand (SiO2), and iron 

(Fe2O3).

•	 Thermal processing: Fuel is combusted at 

the firing end of the kiln, generating gas at 

temperatures in excess of 1,650o

C (3,000oF) that 

travel through the processing equipment. The 

Exhibit 4-1. Cement manufacturing process

Source: Portland Cement Association
39

Chapter 4: Energy Utilization Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

raw material mix is introduced into the opposite 

feed end of the process. Moisture is evaporated 

initially, and the mix is ultimately heated to 

1,450o

C in the burning zone as it travels toward 

the firing end of the kiln. The raw material mix 

undergoes a series of reactions that transforms 

the solid particles into a liquid and allows 

creation of the calcium silicate agglomerates 

about 2.5 cm (1 inch) in diameter, referred to 

as clinker. The clinker is cooled rapidly as it 

leaves the firing end of the kiln. The chemical 

composition of the raw mix must be carefully 

controlled to yield clinker with the required 

chemical and physical properties.

•	 Cement production: Clinker is ground and 

combined with gypsum and other inorganic 

materials to form cement that meets the defined 

performance specifications.

Alternative Kiln Types

The process has evolved to increase thermal 

efficiency, decrease capital costs, and increase 

productivity. Schematics of alternative kiln 

configurations are provided in Exhibit 4-1. The 

following is a brief summary of the process evolution 

and potential for tire and TDF usage in each process:

•	 Long Wet Kilns: A long wet kiln system is the 

top schematic in Exhibit 4-1. Raw materials are 

ground and blended in a wet slurry to achieve 

uniformity. All drying and reactions take place 

in a rotary kiln up to 150 meters (500 feet) 

long. Long wet kilns are expensive to construct, 

operate, and maintain. Evaporating slurry water 

makes the operation extremely energy intensive. 

Whole tires can be introduced into the calcining 

zone of the kiln through a process called midkiln injection. A hole is cut into the kiln with 

internal baffles that prevent product escape. 

As the kiln rotates, a trap door is opened, one 

to three tires drop through the hole, and the 

door closes. An example of the sequence is 

shown in Exhibit 4-2. Shredded tires can also 

be blown into the firing end of kiln through 

a smaller pipe parallel to the main coal firing 

nozzle. Nominal 2.5-centimeter (1 inch) TDF 

is normally used. The TDF system must be 

carefully designed to minimize pipe size and 

additional air while conveying TDF deep into 

the kiln. This prevents reducing conditions 

in the product near the end of the kiln. Both 

of these technologies have been broadly 

applied and are considered reliable and 

proven. 

•	 Long Dry Kilns: Long dry kilns are similar 

to wet systems, but raw materials are 

ground and blended dry to reduce energy 

requirements associated with evaporating 

water from slurry. This results in increased 

productivity and decreased energy 

consumption. The methods for using whole 

tires and TDF are the same as in wet kilns.

•	 Preheater Kilns: A preheater kiln system is also 

shown schematically in Exhibit 4-1. The raw mix 

is preheated more efficiently by contact with 

hot combustion gases in a series of vertically 

stacked cyclones, allowing use of a shorter kiln 

to decrease capital and operating costs. TDF can 

be introduced into the preheater tower. Tires are 

normally injected into the kiln feed end through 

an airlock system. This system is analogous to 

mid-kiln injection in wet and dry kilns because it 

is near the beginning of the calcining zone.

Exhibit 4-2. Mid-kiln injection

Source: North Texas Cement
40

Chapter 4: Energy Utilization Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

•	Preheater-Precalciner Kilns: These kilns are 

similar to preheater systems, but an additional 

stationary combustion chamber is added at the 

bottom of the preheater tower. This additional 

chamber initiates calcining before the kiln and 

further reducing kiln length. This system has 

two combustion zones, one at the kiln firing end 

and the other in the precalciner. The combined 

hot combustion gas streams pass up through 

the preheater tower. TDF can be added into the 

riser section that transports gases from the kiln. 

Whole tires can be introduced through air locks 

into the feed end of the kiln or into the riser duct 

of the precalciner.

The technology for introducing and using whole 

tires and TDF in virtually all types of cement kilns has 

been proven over many years of operation in many 

facilities. Cement kilns have provided a constructive 

and inexpensive use for stockpiled tires in the United 

States, Canada, and many other countries. In fact, 

cement kilns are already using tires removed from 

stockpiles in the border areas of Mexico during 

stockpile abatement. Cement kilns in the United 

States often charge less to accept tires than other tire 

processing facilities or landfill disposal sites.

Logistics

Kilns are geographically dispersed throughout the 

United States and Mexico, with concentrations near 

population centers that generate large quantities 

of waste tires. Exhibit 4-3 shows the distribution 

of cement facilities using tires in the United States. 

Additionally, cement facilities located throughout 

Mexico, are shown in Exhibit 4-4. 

Kilns are near rapidly growing border areas and 

other major industrial centers that generate scrap 

tires. Proximity of kilns to tire generation enhances 

logistical viability by decreasing the transportation 

cost for scrap tires. Transportation costs for whole 

tires and processed products are critical factors in 

constructively using scrap tire materials, as discussed 

in Chapter 6. 

Energy Intensity

Although cement manufacturers have taken 

significant steps to reduce energy consumption, fuel 

is generally the biggest single manufacturing cost. 

Kilns are inherently energy intensive, and each one 

can use 500,000 to 1.5 million tires per year per kiln. 

Based on the U.S. RMA’s kilns statistics cited earlier, 

each kiln using tires in the United States consumed 

an average of about1 million tires in 2007. Tires can 

generally displace 10 to 25 percent of the total fuel 

Exhibit 4-3. U.S. cement facilities using tires

Source: Portland Cement Association
41

Chapter 4: Energy Utilization Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

used in a kiln. Quantity is generally limited by raw 

material or product chemistry, combustion conditions 

within the process (predominantly air availability 

or sulfur build-up) or tire supply. In a competitive 

industry, the energy cost savings of TDF versus fossil 

fuels can provide a significant economic advantage. 

TDF/Whole Tire Metering Systems

Cement kilns are large systems representing sinks 

of energy and materials that create operational 

inertia. Operators strive to maintain steady operating 

conditions and avoid variations that can impair the 

stability of the kiln. Since tires become integrated 

into the clinker product, the iron and other inorganic 

compounds in tires become part of the basic raw mix 

design and must be maintained on a constant basis 

to avoid a negative effect on the cement product. In 

fact, the steel in tires often displaces purchased iron, 

providing another economic savings, but it must be 

fed continuously.

Metering systems have been developed for whole 

and shredded tires to assure continuous, uniform 

supply to the kiln. Whole tire feeding systems can 

be as simple as manual operations that use a cable 

or hook conveyor to raise tires to the kiln floor, with 

people to weigh and insert tires into a simple airlock 

that feeds into preheater or precalciner kilns. These 

systems require limited capital investment, but 

need more labor. They can be useful during trial 

operations to define technical and environmental 

performance. An example of a simple metering 

system to introduce tires into a kiln is depicted in 

Exhibit 4-5.

Most companies in the United States attempt 

to minimize labor costs by making capital 

investments to replace human labor. These 

systems use trailer tippers to dump tires onto 

“singulators” that separate, convey, weigh, and 

insert tires into the kiln with minimal human 

oversight. Some manufacturers of this equipment 

have established reliability standards suitable for 

stable kiln operation, but the installed cost of these 

systems can be US$1 to $2 million per kiln. An 

example of an automated whole tire feed system is 

shown in Exhibit 4-6.

Mid-kiln injection requires a kiln portal and 

automated tire introduction to reduce personnel 

hazards, as shown in Exhibit 4-6.

TDF feed systems for dropping shreds into 

preheater-precalciner kilns generally involve less 

sophisticated handling systems. These can be as 

simple as a skid-mounted metering bin with transfer 

conveyors, weighing equipment, and an airlock. 

There are operational issues, but the equipment 

can be comparatively simple. Systems for blowing 

TDF into the firing end of long wet or dry kilns can 

be a low-capital cost option with a simple metering 

Exhibit 4-4. Mexico cement facilities

30 Plants in 18 Sates
42

Chapter 4: Energy Utilization Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

bin, conveyor, TDF injection piping, and blower. 

However, critical design considerations include the 

need to (1) minimize additional blower air usage 

to control thermal efficiency impact; (2) assure 

deep penetration of TDF into the calcining area of 

the kiln; and (3) avoid nozzle failure by assuring 

continuous air flow through the nozzle.

When metering systems are explored, it is wise 

to obtain a list of previous customers, discuss 

performance with them, and view the systems in 

operation if possible. Use of whole tires or TDF 

can be reliable with proper selection, installation, 

and maintenance of equipment.

Environmental Performance of TDF 

Use by Kilns

The use of tires as TDF amounts to simply burning 

tires in a controlled environment and can be a 

viable option under the correct conditions, as 

demonstrated by diligent monitoring of existing 

operations. Air pollution control regulations 

vary from U.S. state to state; however, analysis 

of emissions data demonstrates that facilities 

remain within permissible limits. Compliance and 

performance monitoring are integral parts to any 

state pollution control program. The following 

factors encourage use of tires as a supplemental 

energy resource in cement kilns, but the application 

also must be environmentally acceptable and not 

pose unnecessary risks to health or the environment. 

Several additional factors that affect environmental 

performance warrant discussion:

•	 Rigorous Combustion Conditions — A 

unique combination of high temperature, long 

residence time, and turbulent air flow promotes 

complete combustion of organic compounds 

in cement kiln systems. Although tires are not 

hazardous wastes, the combustion conditions in 

cement kilns exceed the strict requirements for 

combustion of hazardous wastes in the United 

States. Combustion conditions for tires generally 

exceed 1,450o

C (2,000oF) with air residence times 

in excess of 2 seconds.

•	 SOx Control — Limestone is commonly used to 

absorb SOx in air pollution control systems. It is 

also a major component in the cement raw mix. 

As a result, SOx in combustion gases is captured 

by the limestone in the raw mix as the gases pass 

through the kiln system, thereby providing an 

effective SOx control mechanism. 

•	 Ash Utilization — Ash resulting from tire 

combustion becomes an integral component 

of the cement product, thereby eliminating the 

need to dispose of any ash from TDF combustion.

These factors support use of scrap tires as a 

supplemental fuel in kilns. However, historical 

performance is a critical consideration in evaluating 

environmental acceptability of this application. 

Extensive environmental data have been generated 

for a variety of kiln configurations and alternative fuel 

displacements (for example: scrap tires displacing 

coal as the fuel). 

The following emissions test results are representative 

examples. Performance results for Ashgrove Cement’s 

kiln in Durkee, Oregon, are provided in Table 4-3. 

Emissions of particulates, SOx, chlorides, and all 

heavy metals declined or remained constant. Total 

hydrocarbons increased about 10 percent, but 

polynuclear aromatic hydrocarbons (PAH) declined 

about 10 percent. This facility is fully permitted 

for waste tire usage in Oregon, one of the most 

environmentally sensitive states in the United States. 

Exhibit 4-5. Tire metering systems for kiln introduction

Photo courtesy of Terry Gray, TAG
43

Chapter 4: Energy Utilization Scrap Tires:

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Several cement plants in the southwestern United 

States have undergone extensive testing. Emission 

results for California Portland Cement Company’s 

Colton plant are summarized in Table 4-4. Some 

criteria pollutants decreased with use of tires, while 

others increased. For example, total particulates 

increased less than 10 percent, while non-methane 

hydrocarbons decreased about 18 percent. 

Recognized carcinogens such as benzene and toluene 

decreased. Total dioxins and furans (PCDD/PCDF 

materials) increased very little in quantity. Most 

polychlorinated biphenyls (PCBs) and polycyclic 

aromatic hydrocarbons (PAHs) declined with tire 

usage while hydrochloric and hydrofluoric acids 

increased. Hexavalent chromium, barium, cadmium, 

lead, and nickel emissions declined while zinc and 

mercury increased. The emission testing results 

showed minor changes with a relatively balanced net 

impact.

 California Portland engaged a consultant to 

conduct a comparative health risk assessment. 

The consultant used the latest versions of the 

Industrial Source Complex (ISC) dispersion model 

and U.S. Army Corps of Engineer’s health effects 

model specified by the California EPA to place these 

relative impacts into a technical perspective. Based 

on this evaluation, the individual carcinogenic 

risk declined 47 percent with TDF usage while the 

noncarcinogenic health effects resulting from shortterm exposure (acute hazard index) fell 94 percent 

and the noncarcinogenic health effects of continuous 

exposure (chronic health impact) decreased 72 

percent. Exposure to toxins of any kind is a serious 

and potentially dangerous aspect of today’s society; 

however, the exposure risk reductions demonstrated 

by California Portland Cement Company’s kilns 

demonstrate the effectiveness of this technology as 

a method to use scrap tires and also shows that it 

compares favorably with use of other fuel sources.

Exhibit 4-6. Automated tire feed system components

Photos courtesy of CEMEX Corp
44

Chapter 4: Energy Utilization Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

Cement kilns have collectively used more waste 

tires than any other single application in the United 

States and this application is among the largest 

in Europe and Japan. Furthermore, kilns are an 

important component of waste tire management 

in most U.S. states. Some cement companies in 

Mexico have used, or are using, scrap tires as a 

supplemental energy resource. Cement companies 

in northern Mexico have cooperated with Mexican 

governmental departments to constructively use tires 

removed from border stockpiles under economic 

conditions that were attractive to both government 

and industry. The most critical factors controlling 

development of this application are a consistent 

tire supply and reasonable economics. Cement 

kilns provide an important opportunity for using 

waste tire resources constructively. Any state or 

local government that is not fully utilizing its waste 

tire resource may want to objectively evaluate the 

environmental and economic merits of using scrap 

tires as an energy resource in cement kilns.

PULP AND PAPER INDUSTRY

The pulp and paper industry combusts bark and 

waste wood in stoker-fired boilers to provide 

steam and power required for processing 

operations. Wood is combusted on moving grates 

that also transport residual ash from the boiler. 

Coal, oil, or gas can be fired into the boiler above 

the grate to enhance combustion and to maintain 

operating temperatures when the moisture 

content of waste wood is high from rain.

This application uses TDF obtained by processing 

scrap tires into uniform, flowable chips less than 5 

centimeters by 5 centimeters (2 inches by 2 inches) 

in size. Bead wire is often removed magnetically 

to avoid fouling grates and ash handling systems. 

Representative 5-cm particulate TDF with bead wire 

removed is shown in the photo to the right. 

TDF can be introduced separately or as an integral 

part of the wood mixture with relatively simple, 

inexpensive metering systems. 

TDF can be placed on the feed wood conveyor belt 

to the boiler, as shown in the photograph to the 

right. TDF’s high volatile carbon content enhances 

combustion of wood on the grate and improves fuel 

efficiency.

The environmental impact associated with use of 

TDF in this application depends on characteristics of 

the displaced fossil fuel and system environmental 

control equipment. The two common factors 

controlling environmental acceptability are sulfur 

oxides (SOx) and particulate (zinc oxide) emissions. 

SOx emissions may decrease if TDF displaces coal 

or oil with higher sulfur content. Alternatively, SOx 

can be controlled by the scrubbers present in some 

air filter systems, especially if the scrubbers operate 

at a neutral or basic pH. Particulate emissions can 

be controlled by electrostatic precipitators (ESPs) 

or baghouses. In general, many environmentally 

acceptable applications occur when TDF displaces 

coal in systems with baghouses or ESPs.

Based on data compiled by the U.S. Rubber 

Manufacturers Association in 2007, 32 U.S. paper 

mills used approximately 1.07 million tons of 

TDF, representing about 70 million scrap tires in 

compliance with applicable regulations. Other mills 

are also undertaking testing (Ref. 1). Usage has 

fluctuated, but the high cost of fossil fuels has led to a 

significant resurgence in TDF usage in paper mills as 

TDF particulate with bead wire removed 

Photo courtesy of Terry Gray, TAG

Metering system to introduce TDF into wood mixture before processing 

Photo courtesy of Terry Gray, TAG
45

Chapter 4: Energy Utilization Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

new mills have completed environmental testing and 

existing users have maximized consumption. This is 

especially true for facilities in the southwestern United 

States. 

Table 4-5 provides environmental data associated 

with performance testing conducted at the Bucksport 

site. A baseline test was conducted using the normal 

mixture of gas, bark, coal, and sludge. TDF was then 

substituted for coal at levels representing 6.3 percent, 

10.3 percent, and 14.5 percent of heat input. At the 

maximum TDF level, NOx, SOx, and total hydrocarbon 

emissions remained virtually unchanged while 

particulate matter increased 6 percent. Among the 

metals, beryllium and chromium decreased, lead 

remained below detection limits, and cadmium 

increased. Zinc increased significantly percentagewise, but total quantities remained environmentally 

acceptable. Overall particulate emissions remained 

well within acceptable limits.

Performance data have also confirmed the 

environmental acceptability of TDF in similar 

paper mills and industrial boilers in 20 U.S. 

states. Several of these states (including 

Oregon, Washington, California, and Florida) 

are recognized for their high environmental 

standards and rigorous regulatory enforcement. 

However, these applications must be carefully 

screened to define facilities capable of using TDF 

within environmentally acceptable limits. Only 

a small percentage of paper manufacturing and 

industrial facilities in the United States have the 

required combination of system design, permitting 

Table 4-3 Environmental Performance Data TDF Introduction Into Riser Section 

of Ashgrove Cement’s Preheater Kiln

CRITERION UNITS BASELINE 9% to 10% TDF PERMIT LIMIT

PARTICULATE lbs/hr 5.27 4.83 18

SOx lbs/hr <1.5 <1.2 6.3

CHLORIDES lbs/hr 0.268 0.197 NA

TOTAL 

HYDROCARBONS lbs/hr 3 3.3 NA

POLYNUCLEAR 

AROMATICS (PNA) lbs/hr 0.0058 0.0053 NA

HEAVY METALS

Arsenic micrograms 0.2 0.2 NA

Cadmium micrograms 3 2 NA

Chromium micrograms 30 ND NA

Nickel micrograms 30 ND NA

Zinc micrograms 35 35 NA

Copper micrograms 37 13 NA

Lead micrograms ND ND NA

Iron micrograms 400 200 NA

Barium micrograms ND ND NA

Vanadium micrograms ND ND NA

The International Paper facility in Bucksport, 

Maine, has been one of the largest users of TDF 

since 1990. Its boiler is capable of consuming 

up to 3.5 tons of TDF per hour (14.5 percent by 

heat input) to produce almost 225,000 kilograms 

(500,000 pounds) of steam per hour. 

Conveyor belt to introduce wood and TDF into boiler system

Photo courtesy of Terry Gray, TAG
46

Chapter 4: Energy Utilization Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

conditions, and fuel usage conducive to appropriate 

TDF usage.

PUBLIC UTILITY BOILERS

During 2007, 38 electric power utility and industrial 

facilities were consuming the equivalent of 35 

million tires (495,000 metric tons), according to 

the U.S. Rubber Manufacturers Association (Ref. 1). 

This industry segment continues to increase, with 

additional growth projected in the future. 

TDF can be used efficiently only in specific types of 

utility boilers (primarily cyclone, fluidized-bed, and 

stoker-grate units) that offer adequate retention time 

for complete combustion of nominal 2.5 centimeter 

(1 inch) TDF that is sometimes referred to as “minus 

(finer than) 5 centimeter” (“minus 2 inch”) TDF. This 

Table 4-4 Environmental Performance Data California Portland Cement Kiln 

(Expressed as Pounds/Hour)

CRITERION EXPONENT BASELINE 12%TDF

PARTICULATE 7.35 8.01

NOx (ppm) 208.80 104..2

CO (ppm) 104.20 159.30

VOLATILE ORGANIC COMPOUNDS 

Acetaldehyde 0.34 0.05

Benzene 2.65 2.29

Formaldehyde 0.88 0.11

Toluene 3.98 3.17

Dichloromethane E-3 1.79 0.87

O-xylene E-3 1.89 2.14

Trimethyl benzenes E-3 1.56 3.99

METALS

Antimony E-4 2.32 <2.28

Arsenic E-4 4.05 0.85

Barium E-3 1.20 0.48

Cadmium E-4 2.27 1.77

Chromium (Total) E-4 3.44 3.94

Chromium (Hexavalent) E-4 2.33 1.13

Copper E-3 1.11 0.72

Lead E-3 1.19 0.59

Manganese E-3 1.96 2.06

Mercury E-3 4.54 8.33

Nickel E-4 5.81 3.00

Selenium E-4 ND<1.97 ND<6.54

Silver E-5 ND<3.94 <4.55

Thallium E-5 <2.52 <2.47

Zinc E-3 4.71 9.41

NON-METHANE 

HYDROCARBONS 18.16 14.81

PCDD/PCDF E-6 1.58 1.93

2378 TCDD TOX EQUIV E-8 1.05 1.68

PCBs E-6 3.16 2.89

PAH E-2 4.31 3.44

HCl <0.017 0.43
47

Chapter 4: Energy Utilization Scrap Tires:

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TDF material is the smallest that can generally be 

produced at costs competitive with coal and other 

fossil fuels. These public utility units consume large 

quantities of fuel, so small percentages of TDF (2 to 

4 percent) can use up to 5 million tires per year at a 

single facility. 

This market appears to represent less potential in 

Mexico because of prevalent use of residual oil for 

power generation. Most oil-fired combustion units do 

not need nor have the ash handling and combustion 

chambers required for use of solid fuels such as TDF. 

As a result, detailed discussion of this application does 

not appear to be useful for Mexico, with the possible 

exception of fluidized-bed boilers. 

Circulating fluidized bed boilers represent one of the 

newer systems designed to minimize environmental 

impact from use of solid fossil fuels. High turbulence 

and uniform heat distribution allow fluidized beds 

to operate at lower temperatures to minimize NOx 

formation. Ammonia injection may also be used for 

supplemental NOx reduction. Limestone is commonly 

used as the circulating bed media, providing efficient 

SOx control through integral mixing with combustion 

gases. Sophisticated baghouses or electrostatic 

precipitators remove particulates. These systems 

represent environmentally viable candidates for use 

of nominal 2.5-centimeter (1-inch) TDF. 

The Stockton Cogeneration facility in Stockton, 

California conducted extensive trials with financial 

assistance from the California Integrated Waste 

Management Board to define the emissions 

characteristics associated with use of up to 20 

percent TDF (by heat). The results of this analysis are 

compared with the facility’s existing permit limits in 

Table 4-6. All emissions were well within permit limits, 

with particulate and hydrocarbons at less than 25 

percent of established limits.

Dedicated Tire Combustion Units

Tires have even been used as a primary fuel in 

dedicated, specially designed power boilers in 

California, Connecticut, and Illinois, using 5 to 10 

million tires per year. Although these systems 

use large quantities of tires that must be available 

in a limited geographic area, they are still small 

by power generation standards. As a result, the 

capital costs per megawatt are higher than a 

nuclear power plant. Two of the facilities have 

failed economically and have resulted in major 

capital losses. The Connecticut facility is still 

operating, but it has an abundant tire supply in 

the highest population density area of the United 

States and comparatively high electricity pricing. 

These dedicated systems are unlikely to be 

economically viable in Mexico just as they are not 

viable in the majority of the United States. 

COMBINED ENERGY/MATERIALS 

RECOVERY: PYROLYSIS/GASIFICATION

Pyrolysis is, by definition, thermal decomposition 

of organic compounds in an oxygen-limited 

environment. Promoters have called the pyrolysis 

processes thermal distillation, destructive 

distillation, and many other names to avoid 

identification with historical pyrolysis failures. 

Pyrolysis of waste tires typically generates gas, oil, 

and char products. The quantity and quality of 

each product depend on many process variables, 

including temperature, pressure, and residence 

time. Twenty to 35 percent of a tire’s energy content 

is typically converted into a combustible gas that is 

used to fuel the pyrolysis process or is combusted in 

a flare before it is released. Thirty-five to 50 percent 

of the output from the process is transformed into 

an oil product that varies in quality from saleable 

fuel oil to lower-value oil blend stock. The residual 

solid product (referred to as char) constitutes 25 to 40 

Table 4-5 Comparative Emissions for International Paper Mill Bucksport, Maine 

(Expressed as Pounds/Mbtu)

CRITERION BASELINE 14.5% TDF (BY HEAT) PERCENT CHANGE

NOx 0.274 0.273 0

SOx 0.508 0.51 0

PARTICULATES 0.053 0.056 6

TOTAL HYDROCARBONS 1.17 E-3 1.18 E-3 1

BERYLLIUM 1.06 E-6 0.73 E-6 -31

CADMIUM 0.60 E-6 0.78 E-6 30

CHROMIUM 12.1 E-6 6.36 E-6 -47

LEAD <10 E-6 <10 E-6 0

ZINC 0.26 E-3 2.56 E-3 885
48

Chapter 4: Energy Utilization Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

percent of the output and contains a mixture of the 

following materials:

•	 Multiple types of carbon black used in various

sections of a tire for strength, wear, or other 

critical performance properties.

•	 Titanium dioxide from white sidewalls and

lettering.

•	 Zinc dispersed uniformly within tires as a

vulcanization accelerator.

•	Steel from bead and radial reinforcing wire.

•	Other trace inorganic compounds present in

tires.

Historical Experience

Pyrolysis is not a new process. It was developed 

in Europe more than 60 years ago to transform 

coal into gas for street lamps. Over the past 25 

years, many processes, equipment, and operating 

variations have been applied to scrap tires. A U.S. 

Department of Energy publication titled “Scrap 

Tires: A Resource and Technology Evaluation 

of Tire Pyrolysis and Other Selected Alternate 

Technologies” identified 31 pyrolysis projects 

in 1983 that used fluidized beds, traveling grate 

chambers, rotary kilns, retorts, molten salt and 

hot oil baths, plasma arc units, and microwave 

chambers as reactors. Various operating conditions 

have been extensively explored to optimize 

production and the quality of product streams. In 

spite of this extensive developmental effort, no 

commercial-scale pyrolysis systems currently operate 

continuously in North America.

Extensive technical and economic resources (more 

than $350 million) have been invested in projects 

developed by major companies world wide in 

support of pyrolysis. In addition, many pilot or 

“demonstration” projects have been developed by 

smaller companies and entrepreneurs. One major 

project developed by Foster-Wheeler in England 

(called Tyrolysis) failed technically and economically 

after expenditures that exceeded $30 million.

Major reasons for failure of pyrolysis projects have 

included the following:

•	 Operating Problems: Using complex 

equipment at high temperatures with an 

abrasive feedstock such as scrap tires is 

generally maintenance-intensive. Downtime 

and maintenance expenses have often been 

underestimated in projections of total project 

costs.

•	 Safety: Operating in an oxygen-limited, hightemperature environment creates the possibility 

of fires or explosions if air enters the system 

accidentally. These accidents have destroyed or 

damaged numerous pyrolysis facilities, including 

complete destruction of one operation in Texas.

•	 Feed Availability and Processing: The quantity 

of tires required for economic feasibility can be 

more than are available within an economical 

delivery area at projected net tipping fees. In 

addition, capital and operating costs associated 

with shredding or feedstock preparation are 

often underestimated.

•	 Product Quality: It is difficult to optimize quality 

and yields of three inter-related product streams 

(gas, oil, and char) since conditions that favor 

one often have a negative impact on another. 

Because of the mixture of carbon blacks and 

other constituents, the char has historically been 

The Stockton Cogeneration facility in 

Stockton, California, conducted extensive trials 

with financial assistance from the California 

Integrated Waste Management Board to define 

the emissions characteristics associated with use 

of up to 20 percent TDF (by heat). All emissions 

were well within permit limits, with particulate 

and hydrocarbons at less than 25 percent of 

established limits.

Table 4-6 Emissions From A Circulating Fluidized Bed Boiler Stockton Cogen 

(Stockton, California) (Expressed as pounds/hour)

CRITERION 20% TDF (BY HEAT) LOWER PERMIT LIMIT

NOx 25.06 39.00

SOx 33.40 59.20

PARTICULATES 2.19 10.00

CO 20.90 22.90

TOTAL HYDROCARBONS <0.38 1.88
49

Chapter 4: Energy Utilization Scrap Tires:

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suitable only for low-value applications with 

limited market volumes, even when the char is 

further processed to control size uniformity and 

iron content.

•	 Environmental Impact: Tires contain about 

1.8 percent sulfur and 1.2 to 1.5 percent zinc 

by weight. These inorganic materials are not 

destroyed or decomposed thermally, so they 

remain in one or more of the pyrolysis products 

as dictated by an elemental mass balance for 

specific operating conditions. In addition, 

partially decomposed hydrocarbons may not 

be fully removed from the exhaust gas stream 

by condensation or combustion. As a result, 

pyrolysis systems must include air pollution 

control systems to prevent discharges to the 

environment. Pyrolysis promoters often claim 

that their process has no emissions because all 

materials are captured as products. However, 

the gas product is generally combusted to fuel 

the process or flared on site because it cannot 

be transferred in normal gas transmission lines. 

In either case, combustion creates emissions 

that require controls to comply with clean air 

standards in the United States. In addition, the 

char may require disposal as a hazardous waste 

if it is not marketable. These practical realities 

should be reflected in capital and operating cost 

projections.

•	 Economics: The economic feasibility of pyrolysis 

depends on many operating factors. These 

factors include system reliability, capital and 

labor costs, process, feedstock preparation 

expense, environmental control requirements, 

and product revenue. Past operations have not 

been economically sustainable at reasonable 

tipping fees because they have not been able to 

develop high-value (about 3.5 pesos or $0.33 per 

kilogram [$0.15 per pound]) markets for all of the 

char generated. The materials recovery appeal 

and economic viability of this process depend 

totally on being able to sell the carbon black 

content of the char stream at a relatively high 

price. Unless this objective is achieved, pyrolysis 

simply becomes a capital-intensive process for 

conversion of a solid fuel into a low-grade liquid 

fuel.

Current Practice

Many companies are promoting pyrolysis systems 

in North America. None of these technologies has 

been practiced on a commercial scale for an adequate 

period of time to fully demonstrate long-term 

operating economics and char marketability. It would 

be even more difficult to achieve economic viability 

with the low tipping fees likely to be encountered in 

Mexico. 

One variation of pyrolysis refines the oil stream into 

high-value specialty chemical products. The product 

gas from the reactor is cooled in a heat exchanger, 

thereby condensing a broad range of partially 

decomposed chemical compounds to form “oil” 

suitable for use primarily as a low-value blend stock. 

The high capital cost and sophisticated control of 

multiple condensers or fractionation equipment 

required to produce and refine multiple liquid 

products are economically questionable for these 

relatively small oil volumes. Refining operations 

require high volumes to be economically viable. 

The oil generated by a large pyrolysis system using 

2 million tires per year would represent less than 1 

percent of refinery throughput required to operate 

at minimum capacity.

Gasification Variation

A variation of pyrolysis allows some air to be 

present to facilitate partial combustion. This 

drives the gas, oil, and char into a low heat 

value gas that contains predominantly carbon 

monoxide with some hydrogen and low 

molecular weight hydrocarbons. This gas is then 

burned to generate steam or power by many 

alternative methods, many of which are not 

economically practical at the projected scale of 

operation or with the particulate and chemical 

contaminants present in the gas. Although this 

variation overcomes the issue of char marketability 

by driving the carbon to carbon monoxide, it does 

not overcome air emissions issues when the gas 

is combusted. This process is simply two-stage 

combustion and must account for air emissions 

and material balances, as with the combustion 

applications. There are no known commercial-scale 

tire gasification system units operating on a selfsustaining economic basis in North America as of 

November 2009.

Summary and Recommendations

Tire pyrolysis and gasification facilities have not 

been able to demonstrate and sustain economic 

viability historically because of technical failures or 

the inability to obtain contractual commitments 

for all char products. Many pyrolysis facilities have 

failed during the past 20 years, generally leaving a 

government liability for abatement of accumulated 

tires as well as remediation of residual oil and char 
50

Chapter 4: Energy Utilization Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

contamination. Requiring financial assurance to 

cover alternative disposal costs for maximum stored 

quantities of tires and char can be one appropriate 

method of protecting public interests. 

Investors should conduct thorough due diligence 

before they make substantial equity or debt 

commitments to this technology. Critical questions 

about product quality, markets, safety, maintenance 

expense, and economics must be answered before 

this technology can be considered a proven 

alternative for disposal of scrap tires. 

SUMMARY

Scrap tires can be an environmentally compatible 

alternative energy resource when used in 

appropriate applications. Energy use is an 

important component of successful scrap tire 

management programs within the United 

States in allowing this resource to be used 

productively. The net result has been substantial 

conservation of non-renewable fossil fuels. When 

the demonstrated performance of tires as an 

energy resource is objectively evaluated, many 

jurisdictions have concluded that the environment 

is better served by recognizing the value of this 

resource rather than wasting it while waiting for 

ideal solutions. Good scrap tire management 

programs recognize the importance of diverse 

applications.

Ideally, a tire’s polymerized rubber mixture 

would be perpetually reused. However, today’s 

applications for recycled rubber consume less than 

17 percent of the waste tires generated annually 

in the United States. These markets are growing 

slowly in spite of intense market development 

efforts, and even the most optimistic projections 

show less than 25 percent use in 5 years. 

Other major applications for scrap tires must be 

embraced and developed to constructively use 

this resource, or it will be squandered through 

landfilling or become a stockpiled public liability 

that poses public health and environmental hazards. 

Since few consciously want to waste a valuable 

resource, other applications that are compatible with 

the environment should become the foundation of 

market development efforts. Avoiding unnecessary 

consumption of these limited natural resources 

through use of scrap tires as an alternative energy 

resource is a worthy objective if it can be done 

without a counter-balancing negative impact on the 

environment.

REFERENCES

1. Scrap Tire Markets in the United States, Rubber 

Manufacturers Association, 2008

2. “Energy Use in the Cement Industry in North 

America, Emissions, Waste Generation and 

Pollution Control, 1990-2001,” 2003, p11. (www.

cec.org/files/pdf/ECONOMY/Session1-2-JacottReed-Winfield_en.pdf)

3. “Air Emission Data Summary for Portland Cement 

Pyroprocessing Operations Firing Tire-Derived 

Fuels.” 2008. www.epa.gov/osw/conserve/

materials/tires/pubs/tdf-report08.pdf (PDF)
51

Chapter 5: Tire Derived Aggregate and Whole Tires for Civil Engineering Applications Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

Tire derived aggregate (TDA) is an engineered 

product made by cutting scrap tires into 25- to 

300-millimeter (mm) pieces. In the United States in 

2004, 60 million tires were used as TDA (Ref. 37). TDA 

provides many solutions to geotechnical challenges 

since it is lightweight (50 pounds per cubic foot 

[pcf]; 0.8 macrograms per cubic meter [Mg/m3

; note 

that the capital M distinguishes the acronym from 

the commonly understood micrograms per cubic 

meter]), produces low lateral pressures on walls 

(as little as one-half that of soil), is a good thermal 

insulator (eight times better than soil), has high 

permeability (more than 1 centimeters per second 

[cm/s] dependent on TDA size), has good shear 

strength, and absorbs vibrations. When used in 

appropriate applications, TDA’s special properties can 

greatly reduce construction costs. Moreover, each 

cubic meter of TDA fill contains the equivalent of 100 

passenger car tires.

TDA has been economically used for a wide range 

of functions in the United States. For example, 

it has been used as lightweight fill for highway 

embankments in 13 states. In the State of Maine, 

TDA is routinely used to improve the stability of 

embankments constructed on weak, marine clay, 

resulting in an average annual consumption of about 

1 million passenger car tires (Refs. 8, 19, 27, 28, 41, 46, 

49). TDA and TDA soil mixtures have also been used 

as a replacement for conventional soil in embankment 

construction (Refs. 15, 16, 43). The low unit weight 

and resulting low earth pressure, combined with its 

high permeability, make TDA an attractive backfill 

for retaining walls, bridge abutments, and sheet-pile 

walls (Refs. 19, 28, 45, 46). TDA has also been used 

as compressible layers behind integral abutment 

and rigid frame bridges (Refs. 27, 38). In this regard, 

Maine, Louisiana, Pennsylvania, and California 

have used TDA in retaining wall projects. In cold 

climates, TDA has been used to limit the depth of 

frost penetration and to provide drainage during 

the spring thaw (Refs. 20, 32). Furthermore, the 

permeability of TDA has led to significant use as 

drainage layers in landfills (Ref. 30), septic system 

drain fields, and highway edge drains (Ref. 32). Recent 

research has shown that a TDA layer beneath the 

stone ballast of rail lines reduces off-site vibrations 

that can affect adjoining residences and businesses 

(Ref. 51). This new technology was used on a lightrail commuter transit line recently completed in 

San Jose, California. Finally, a promising new idea 

for using TDA as backfill for bridge abutments to 

reduce earthquake loading was investigated by the 

University of California at Davis (Ref. 29).

The economics of using TDA for civil engineering 

applications depend on the local costs to produce 

TDA, as discussed in Chapter 6, and the local costs 

for competing alternative construction materials. 

TDA is generally cost competitive for projects 

that require use of lightweight fill material for 

embankment construction. Moreover, use of 

TDA in drainage applications is cost effective 

in areas where there is a limited supply of 

conventional drainage aggregate. TDA is not, 

however, a generally cost-effective substitute for 

conventional earth fill.

Guidelines and construction specifications are 

available to help engineers take advantage of 

the special engineering properties of TDA. Most 

important of these is ASTM International Standard 

D6270-98 (Ref. 3), Standard Practice for Civil 

Engineering Applications of Scrap Tires (www.

astm.org/Standards/D6270.htm). This document 

lists the typical geotechnical properties of TDA, 

applicable test methods, and construction 

guidelines. Several studies have also shown 

that TDA has negligible impact on groundwater 

(see for example Refs 4, 5, 9, 10, 15, 16, 21, 22, 

40). A statistical analysis of the effect of TDA on 

groundwater is presented in Humphrey and Swett 

(Ref. 26).

Use of TDA as drainage aggregate and lightweight fill

will be presented in the following sections. The level 

of sophistication in specific applications varies. Some 

applications are for large civil engineering projects 

that must be designed by qualified engineering 

professionals. Other applications are small scale and 

can be implemented by municipal officials such as 

public works directors. Recommended materials 

specifications are presented in Appendix A. TDA with 

a maximum size of about 75 mm (3 inches) is referred 

CHAPTER 5

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for Civil Engineering Applications
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to as Type A TDA, while TDA with a maximum size of 

about 300 mm (12 inches) is referred to as Type B TDA. 

Type A TDA is appropriate for a range of drainage 

applications in layers up to 1 m (3.3 feet) thick. Type 

B TDA is used for lightweight fill applications in layers 

up to 3 m (10 feet) thick. Three TDA projects in 1995 

and 1996 underwent internal heating reactions, which 

prompted development of engineering guidelines 

to limit internal heating of TDA fills. The guidelines, 

as well as discussion of possible causes, are included 

as Appendix B. Experience on full-scale projects has 

shown that these guidelines are effective (Ref. 18). 

The engineering properties of TDA are discussed 

in detail in Appendix C. Use of whole tires for civil 

engineering applications is also discussed in this 

chapter.

TDA AS DRAINAGE AGGREGATE

TDA can be used as a substitute for conventional 

drainage aggregate for a wide range of 

applications. This material is advantageous when 

conventional aggregate is more expensive or 

is unavailable. Potential drainage applications 

include:

•	Drainage layers within landfill leachate collection

and removal systems.

•	Permeable aggregate for landfill gas collection

layers and trenches.

•	Free draining aggregate for edge drains for

roadways.

•	Permeable backfill for exterior walls below the

ground surface.

•	 Septic system drain fields.

TDA with a maximum size of 75 mm (3 inches) is 

appropriate for most of these applications. 

The most important engineering property for 

drainage applications is permeability, also known as 

hydraulic conductivity, a measure of the capacity of 

a material to transmit a fluid. Permeability is related 

to void ratio, which is a measure of the void space 

between the aggregate particles. The fluid flows 

through the void space. For both of these properties, 

the void ratio, and in turn the permeability decreases 

as the vertical stress increases. These properties 

will be discussed in detail in Appendix C. However, 

key results are reviewed in this section. As shown 

in Exhibit 5-1, the void ratio of compacted TDA is 

between 0.8 and 0.9. However, the void ratio is less 

than 0.1 at stresses above about 400 kiloPascals (kPa) 

(9,000 pounds per square foot [psf]). This ratio stress 

corresponds to about 23 m (75 feet) of overlying 

soil fill. At void ratios this low, even a small amount 

of clogging could result in a significant decrease 

in permeability. Therefore, it would be reasonable 

to set 0.2 as a lower limit for void ratio for many 

applications, which corresponds to the void ratio of 

well-graded clean sand. The void ratio restriction 

would limit use of TDA in drainage applications to 

vertical stresses less than about 240 kPa (5,000 psf). 

Stresses this high could be encountered for some 

applications where TDA is used as a drainage layer 

in a landfill leachate collection and removal system. 

However, stresses in other landfill and roadway 

applications will likely be less than this limiting value.

The permeability of TDA decreases as the void ratio 

decreases, as shown in Exhibit 5-2. The permeability 

will be greater than 1 cm/s at void ratios typical of 

highway applications (greater than 0.4). At a void 

ratio of 0.2, the permeability is about 0.25 cm/s, 

which is adequate for most drainage applications. 

For comparison, the permeability of well-graded 

clean sand is typically 1 x 10-2 cm/s (Ref. 14), so TDA is 

more permeable than many readily available granular 

materials.

The use of TDA in specific drainage applications will 

be discussed in the following subsections.

Landfill Leachate Collection and 

Removal Systems

New municipal solid waste landfills (MSWLF) are 

generally designed with a composite liner to limit 

outward migration of leachate, and a leachate 

collection and removal system (LCRS) that is designed 

to maintain less than 300 mm of leachate over the 

liner (see Subtitle D landfill regulations at Title 40 

Code of Federal Regulations [CFR] Part 258.40(a)). 

Approximately half of the U.S. states require that 

aggregate used for a LCRS have a permeability 

greater than either 1 x 10-2 cm/s or 1 x 10-3 cm/s 

(Ref. 31). In addition, the LCRS should be designed 

to function without clogging throughout the life 

of the landfill and the post-closure maintenance 

period (see, for example, Title 27 of the California 

Code of Regulations). Moreover, the aggregate 

must be stable on side slopes. Finally, the aggregate 

should not damage the underlying composite liner 

during construction and operation. TDA used as a 

component in an LCRS should have a maximum size 

of 75 mm (3 inches) and meet the requirements for 

Type A TDA given in Appendix A. Textbooks such 

as “Geotechnical Aspects of Landfill Design and 
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Exhibit 5-1. Void ratio vs. vertical stress for Type A TDA 

Exhibit 5-2. Permeability vs. void ratio for Type A TDA
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Construction” by X. Qian, R.M. Koerner, and D.H. 

Gray, Prentice Hall, 2002, and applicable government 

regulations should be consulted for general principals 

and specific requirements of LCRS design. In the 

following section, only those aspects that are specific 

to the use of TDA are discussed.

The permeability of TDA is adequate for many LCRS 

applications and will generally exceed 1 x 10-2 cm/s. 

However, the TDA layer is compressed by the 

weight of the overlying waste and its void ratio 

is decreased. At high stresses, the void ratio can 

decrease to less than 0.1, as shown in Exhibit 5-1. 

The TDA would be susceptible to clogging at void 

ratios this low. A minimum void ratio of 0.2 is 

therefore recommended. This ratio would limit 

the vertical stress caused by the overlying material 

to about 240 kPa (5,000 psf). An in-place unit 

weight of municipal solid waste (MSW), including 

a reasonable amount of daily soil cover, would 

typically be 0.8 to 1.1 Mg/m3 (50 to 70 pcf) 

(Ref. 36). This weight will limit the thickness of 

overlying waste to about 20 m to 30 m (70 feet to 

100 feet).

The compressibility of the TDA must be 

considered in selecting the TDA layer thickness. 

In general, the layer must be overbuilt to 

compensate for compression under the weight 

of the overlying MSW, so that the thickness 

of the layer will meet design requirements after 

compression. Table 5-1 should be used for guidance 

in determining the amount of overbuild.

In addition, steel bead wire protruding from the 

cut edges of TDA can puncture the underlying 

geomembrane. Bead wires are the stiff bundle 

located where the tire contacts the rim. The 

possibility that bead wires could puncture 

geomembrane was investigated in a field trial 

conducted by the California Department of Resources 

Recycling and Recovery (CalRecycle; Refs. 11, 12). Test 

sections were constructed with TDA placed directly 

on geomembrane, separated from the geomembrane 

with geotextile with weights up to 1,620 grams per 

square meter (g/m2

) (48 ounces per cubic yard [oz/

yd2]), and separated from the geomembrane with 

drainage geocomposite. The installation was tracked 

with 100 passes of a Caterpillar D-7G bulldozer with 

an operating weight of approximately 20,400 kg 

(45,000 pounds). In all cases, the exposed steel bead 

wire punctured the underlying geomembrane even 

when protected by geotextile or geocomposite. An 

example puncture is shown in Exhibit 5-3. However, 

a test section with 300 mm (12 inches) of gravel as a 

separator between the TDA and the geomembrane 

showed no signs of puncture (Refs. 11, 12). Thus, the 

TDA for liner systems that contain a geomembrane 

should be separated from the geomembrane by at 

least 300 mm (12 inches) of conventional drainage 

aggregate. Alternatively, the tire can be debeaded 

before it is shredded in regions with low labor costs, 

and the restrictions discussed in the next paragraph 

can be followed.

The field trial conducted by CalRecycle (Refs. 11, 12) 

showed that finer belt wire that is located in the tread 

and sidewall portions of the tires does not puncture 

the geomembrane. However, belt wire can create 

some minor indentations, scratches, and dents in 

direct contact with the geomembrane. Although not 

confirmed by testing, it is thought that this minor 

damage may reduce the tensile strength of the 

geomembrane (Refs. 11, 12). The TDA may be placed 

in direct contact with the geomembrane if the bead 

wire has been completely removed in flat areas where 

the tensile strength of the geomembrane is of little 

Table 5-1. Compressibility of Type A TDA.

Vertical stress

kPa (psf)

Vertical

compression (%)

69 (1440) 19-33

138 (2880) 25-37

207 (4320) 29-42

276 (5760) 33-44

345 (7200) 36-46

414 (8640) 39-48

483 (10,080) 40-50

Table adapted from GeoSyntec (1998b); source of data Manion 

and Humphrey (1992) and Humphrey and others (1993)

Exhibit 5-3. Example of steel bead wire puncturing geomembrane (Ref. 12)
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importance. The geomembrane should be protected 

with geotextile (270 g/m2 (8 oz/yd2) or heavier) 

on side slopes where the tensile strengths of the 

geomembrane is important.

A typical design that incorporates TDA as a 

component in the LCRS would be 300 mm (12 inches) 

of conventional drainage aggregate overlain by 

300 mm to 450 mm (12 to 18 inches) of Type A TDA. 

The compressed thickness of the TDA layer would 

generally be 300 mm (12 inches) or greater. The 

TDA would typically be spread in a single lift (layer) 

with a low-ground contact pressure bulldozer. The 

layer should be compacted by four passes of the 

bulldozer. A geotextile should be used as a separator 

to minimize infiltration of fines for TDA placed 

directly on a compacted low-permeability soil layer. 

A 1-hectare TDA drainage layer that is 450 mm (18 

inches) thick would require the equivalent of 300,000 

passenger car tires.

Landfill Gas Collection Systems

Landfill gas (LFG) collection systems are used to 

collect landfill gases and convey them directly to 

the atmosphere or to a central location where they 

are burned. LFG is collected by one or more of the 

following features: horizontal blankets of permeable 

aggregate placed beneath the intermediate or final 

cover; horizontal trenches of permeable aggregate 

located within the landfill; or vertical wells filled 

with permeable aggregate. A perforated pipe may 

be used in conjunction with permeable aggregate 

to increase the extraction capacity. LFG collection 

systems may be passive, so that the permeable 

aggregate simply provides a pathway to convey the 

LFG to the atmosphere; or active, so that a vacuum 

is used to extract the LFG from the landfill. The high 

permeability of TDA allows it to be substituted for 

conventional aggregate in many LFG collection 

applications. The general principles of LFG collection 

system design are presented in texts such as Qian 

and others (Ref. 36) and applicable governmental 

regulations.

TDA Gas Collection Blanket

Several factors must be considered when TDA is used 

as a gas extraction blanket placed beneath a final 

cover system. For most applications, the blanket 

will be covered by less than 1 m (3.3 feet) of earthen 

materials. Thus, the vertical stress on the blanket 

will generally be less than 20 kPa (400 psf). Exhibit 

5-1 indicates that the void ratio at this stress would 

likely be greater than 0.6. Exhibit 5-2 indicates that 

the permeability would likely be greater than 1 

cm/s. These values are comparable to conventional 

aggregate used in this application. The compression 

of the TDA under the weight of the overlying cover 

also must be considered. Although the compression 

will be small at low stresses, it is recommended that 

the as-placed thickness of the layer be increased by 

10 percent to compensate for the compression that 

will occur under the weight of the overlying cover. A 

geotextile should be used to separate the TDA gas 

collection layer from an overlying earth cover. Type A 

TDA is appropriate for this application. The material 

specifications for Type A TDA are listed in Appendix 

A.

The TDA layer should be spread on a properly 

graded and compacted foundation layer 

constructed of soil. The TDA can be spread as a 

single lift. It should be compacted by six passes of 

a vibratory smooth-drum roller with a minimum 

operating weight of 9.8 metric tons (10 U.S. tons).

The compressibility of the TDA gas collection 

layer presents several issues for placement of the 

overlying cover system. A field trial conducted for 

CalRecycle (Refs. 11, 13) found that construction 

of a compacted clay liner (CCL) base consisting 

of 300 mm (12 inches) of compacted soil 

underlain by 300 mm of TDA resulted in a CCL 

that developed excessive cracks. Increasing 

the compacted soil base to 450 mm (18 inches) 

provided an adequate surface for construction of 

the CCL with a hydraulic conductivity of 1 x 10-6

cm/s or less (Ref. 13). Thus, a minimum thickness 

of 450 mm (18 inches) of compacted soil must be 

spread on the TDA gas collection layer to form a 

soil base for construction of the overlying CCL. 

A geotextile should be installed as a separator 

between the TDA gas collection layer and the 

overlying soil base layer.

Some landfill designs call for a geomembrane 

as the barrier layer in a landfill cap system. The 

geomembrane cannot be placed directly on the 

TDA gas collection layer because of the risk of 

puncture from steel belt wire exposed at the cut 

edge of the tire chips. Moreover, the compressibility 

of the TDA would make it difficult to construct 

seams between adjoining geomembrane sheets 

and to maintain the integrity of the seams during 

subsequent construction operations. For these 

reasons, a 300-mm (1-foot)-thick compacted soil 

base layer should be spread on the TDA before the 

geomembrane is put in place. A geotextile should be 

placed as a separator between the TDA gas collection 

layer and the overlying soil base layer.
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TDA Gas Collection Trench

TDA can be used in place of conventional aggregate 

for many LFG collection trench applications. Gas 

collection trenches can have several configurations. 

They include trenches at periodic intervals within 

the waste; trenches excavated through intermediate 

soil cover layers; and gas removal sumps placed at 

the bottom of landfills. For these configurations, 

a perforated pipe is generally surrounded by a 

permeable aggregate. The aggregate must be 

permeable enough to convey LFG to the extraction 

pipe and provide protection for the pipe itself. LFG 

collection trenches may need to operate for only 

a finite period of time, and a geotextile separation 

layer is generally not used. In cases where the 

trench is expected to be operational under 

waste thicknesses greater than 30 m (100 feet), 

consideration should be given to the adequacy 

of the compressed void ratio and permeability. 

The dimensions of the LFG collection trench 

and perforated pipe should be set based on the 

expected rate of gas generation and engineering 

principles such as discussed by Qian and others 

(Ref. 36). There are many successful applications 

in the United States where TDA has been used as 

backfill for LFG collection trenches.

TDA Gas Extraction Wells

The initial step in construction of a vertical gas 

extraction well is typically to drill a hole into the 

landfill using a 0.6- to 0.9-m (2- to 3-foot)-diameter 

bucket auger. A schedule 80 perforated polyvinyl 

chloride (PVC) pipe with a diameter between 100 

and 150 mm (4 to 6 inches) is placed in the center 

of the hole and the annular space is backfilled 

with 25- to 50-mm (1- to 2-inch)-diameter washed 

stone (Ref. 36). It is possible that Type A TDA could 

be substituted for the washed stone.

There will be minimal compaction of the TDA for 

this application. Therefore, it is expected that the 

in-place unit weight at the time of placement would 

range between values for loose, uncompacted TDA 

and compacted TDA. The uncompacted unit weight 

of Type A TDA typically ranges from about 0.4 to 

0.5 Mg/m3

 (25 to 31 pcf). However, uncompacted 

unit weights as low as 0.34 Mg/m3

 (21 pcf) have 

been reported for shreds with an excessive amount 

of exposed steel belts. The compacted unit weight 

of Type A TDA is typically about 0.64 Mg/m3

 (40 

pcf) (Refs. 2, 24, 33). It is expected for the proposed 

application that the in-place unit weight when it 

is placed will range between 0.4 and 0.64 Mg/m3

(25 and 40 pcf). The self-weight of the TDA will be 

largely supported by the side of the borehole, so little 

compression of the TDA as a result of the self-weight 

and the weight of overlying material is expected. 

However, it is expected that the TDA will compress 

over time by the same amount as the adjoining waste. 

Assuming that the waste compresses 20 percent 

over the active life of the collection well, the final 

unit weight of the TDA is expected to range between 

0.5 and 0.8 Mg/m3

 (31 and 50 pcf). This amount of 

compaction corresponds to void ratios between 

0.50 and 1.4. The void ratio of washed stone would 

typically be about 0.43. Thus, the in-place void ratio 

of TDA is expected to be larger than for 25- to 50-mm 

(1- to 2-inch)-diameter washed stone.

The permeability of TDA with a void ratio of 0.50 

would be greater than about 9 cm/s based on Exhibit 

5-2. Permeability data for TDA with a void ratio of 1.4 

are unavailable, but permeability is expected to be 

high. Overall, the void ratio and permeability data 

indicate the performance of that Type A TDA and 

25- to 50-mm (1- to 2-inch)-diameter washed stone 

will be similar to backfill for vertical gas collection 

wells. There are currently no known projects in the 

United States where TDA was used as the permeable 

aggregate placed in vertical boreholes.

An alternative installation procedure was used for 

TDA as the backfill for vertical gas collection wells in 

the Yolo County Central Landfill (YCCL) in California. 

The wells in this landfill were installed as the waste 

was placed. The general construction procedure was 

to use wire mesh to form a 1.2-m (4-foot)-diameter 

cylinder where the TDA was placed. Perforated pipe 

was located in the center of the TDA. The level of 

the TDA was always kept above the adjoining waste 

during construction. The TDA was termed “rough 

shreds,” and its maximum size was greater than 300 

mm (12 inches). These wells have been in successful 

operation for many years.

Drainage Applications for Major

Highways

Excess water in the base of paved roads can 

significantly decrease their service life. TDA can 

be used in two ways to help remove water from 

the roadway cross section. The first is a permeable 

drainage layer beneath the conventional aggregate 

base course. The TDA must be covered by between 1 

and 1.5 m (3.28 and 5 feet) of conventional aggregate 

to minimize the influence of the TDA’s compressibility 

on the performance of the overlying pavement for 

paved roads with heavy traffic volume. Thus, the TDA 

for this application must be located relatively deep in 

the pavement cross section. 
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The second application using TDA is as a replacement 

for conventional drainage applications in highway 

edge drains. These drains are located beyond the 

edge of the traveled way, so the restriction on the 

thickness of overlying cover does not apply. The 

conventional aggregate base course should drain 

into the edge drain. Use of edge drains is particularly 

appropriate in cut sections where it is not possible to 

obtain gravity drainage to an adjoining ditch and in 

locations where the groundwater table is high, as well 

as in urban locations where construction of perimeter 

ditches is impractical.

Drainage layers beneath paved roads should consist 

of 300 mm (12 inches) of Type A TDA (75-mm [3-inch] 

maximum size). It should be placed as a single lift 

and compacted with six passes of a vibratory smooth 

drum roller, smooth drum static roller, sheep or 

tamping foot roller, or bulldozer with conventional 

width tracks. The minimum operating weight should 

be 9.8 metric tons (10 U.S. tons) for each type of 

equipment. To minimize infiltration of surrounding 

soil, the TDA should be encapsulated with permeable 

geotextile meeting the requirements of American 

Association of State Highway Transportation Officials 

(AASHTO) M288, Class 2. Additional information 

on AASHTO requirements is available as part 

of the compilation, “Standard Specifications for 

Transportation Materials and Methods of Sampling 

and Testing, 30th Edition and AASHTO Provisional 

Standards, 2010 Edition” available at https://bookstore.

transportation.org/item_details.aspx?ID=1597. 

TDA for edge drains should be Type A with a 

maximum size of 75 mm (3 inches). It should be 

placed in 300-mm (12-inch) lifts, and each lift should 

be compacted with six passes of a walk-behind roller 

with a minimum operating weight of 1 metric ton (1 

U.S. ton). To minimize infiltration into surrounding 

soil, the TDA should be encapsulated with permeable 

geotextile meeting the requirements of AASHTO 

M288, Class 2. The slope at the bottom of the trench 

should be 1 percent or greater toward a drainage 

outlet. The drainage capacity of a trench with this 

slope and a cross-sectional area of 1square meter (m2) 

will be in excess of 1 cubic meter per second (m3/sec). 

If this capacity is inadequate, then a perforated pipe 

may be incorporated into the base of the edge drain.

Drainage Applications for Local Roads

The general principles for using TDA for drainage 

applications for local roads are similar to those for 

major highways. However, local roads will have lower 

traffic volumes and in some cases may be unpaved. 

For paved roads with low traffic volume, 0.75 m (2.5 

feet) of aggregate base course should be placed over 

TDA drainage layers. Moreover, the TDA for paved 

roads should be separated from the surrounding 

soil by geotextile that meets the requirements of 

AASHTO M288, Class 2. For unpaved roads with low 

traffic volume, 0.6 m (2 feet) of aggregate base should 

be spread over TDA drainage layers; the use of a 

geotextile separation layer is optional.

The use of TDA as permeable aggregate for edge 

drains for local roads is the same as for major 

highways, with the exception that use of a geotextile 

separation layer is optional for unpaved roads.

Drainage Applications for Small-Scale 

Municipal Construction

Permeable aggregate is needed in several 

applications for small-scale municipal construction. 

In some cases, Type A TDA can be substituted 

for conventional drainage aggregate. This 

substitution is advantageous when conventional 

aggregate is more expensive or is unavailable. 

Possible applications include:

•	 Backfill for walls less than 1 m (3.3 feet) high.

•	 Backfill around the foundation walls for

buildings.

•	 TDA-filled trenches in lieu of small-diameter

culverts to convey small quantities of storm 

runoff to convenient discharge locations.

The TDA for these applications can be placed by 

hand or by available construction equipment. The 

TDA should be placed in 300-mm (1-foot) lifts and 

compacted by a hand tamper. Use of a geotextile 

separator between the TDA and the adjoining soil 

is optional, but it would prolong the service life of 

the installation by limiting inward migration of soil, 

which would reduce the permeability of the TDA. 

The TDA should be covered by a minimum of 300 

mm (12 inches) of soil for areas that will be covered 

by vegetation, 450 to 600 mm (18 to 24 inches) of 

base course aggregate for unpaved areas that will be 

subjected to low traffic volumes, and 600 to 750 mm 

(24 to 30 inches) of base course aggregate for paved 

areas that will be subjected to low traffic volumes.

TDA should not be used as fill beneath buildings since 

the compressibility of the TDA could cause structural 

damage to the overlying building. TDA with exposed 

steel bead or belt wire should never be left exposed 

at the ground surface because of the risk of cuts and 

punctures to humans and other animals.
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Drainage Applications for Septic 

System Drain Fields

Given the permeable nature of TDA, it has become an 

attractive option to replace traditional stone backfill 

material within septic system drain fields. Several 

U.S. states have begun allowing its use for new 

construction of these drainage fields. It has been 

found to reduce the expense and labor needed to 

construct traditional systems, and TDA is capable of 

holding more water than is stone. Transportation of 

the material is also more efficient and easier given its 

light weight. TDA can be a beneficial option in areas 

with abundant scrap tire supplies and where stone is 

not readily available and is expensive to transport. 

TDA AS LIGHTWEIGHT FILL

The low in-place unit weight and relatively low 

cost make TDA an attractive lightweight fill for 

embankments constructed on weak ground, 

landslide stabilization, and retaining wall backfill. 

Proper use of TDA as lightweight fill can result in 

an increased factor of safety against a global slope 

stability failure, reduced-long term settlement, 

and lower construction costs. Since each cubic 

meter of TDA fill contains the equivalent of 

100 passenger car tires, even relatively small 

projects can consume large quantities of tires. 

For example, 1.2 million passenger car tires (PTE; 

passenger tire equivalents) were used for the 

approach fills for a highway overpass in Portland, 

Maine. Design considerations for use of TDA 

as lightweight fill are provided in the following 

section. Then, specific applications of TDA as 

lightweight fill are discussed. As previously 

mentioned, the internal heating of TDA has 

the potential to cause a reaction; however, the 

potential is greatly decreased if the engineering 

specifications discussed in Appendix B are 

followed. Any project using TDA as lightweight fill 

must be designed by a geotechnical engineer who 

is well versed in soil properties, stability analysis 

techniques, and settlement calculation methods.

Design Considerations for use of TDA 

as Lightweight Fill

There are several special considerations for design 

of projects using TDA as lightweight fill. These 

considerations include estimating the final in-place 

unit weight of the TDA, calculating the overbuild 

of the TDA layer needed to compensate for 

compression under the weight of overlying materials, 

estimating the required thickness of overlying soil 

cover, and following guidelines to limit internal 

heating. These considerations are discussed in the 

following subsections. A detailed discussion of the 

engineering properties of TDA is given in Appendix 

C. Many of these properties will be necessary for 

the geotechnical design of TDA lightweight fills. A 

procedure for estimating the final in-place unit weight 

of TDA and overbuild is given in Appendix D.

Thickness of Overlying Soil Cover

Sufficient soil cover must be placed over the 

compressible TDA layer to preserve the durability of 

the overlying pavement, as investigated by Nickels 

(Ref. 34) and Humphrey and Nickels (Ref. 25). Cover 

thickness is defined as the combined thickness of 

base course and soil measured from the bottom 

of the asphaltic concrete pavement to the top of 

the TDA layer. Computer modeling showed that 

the tensile strain at the base of asphaltic concrete 

pavement with 760 mm (30 inches) of soil cover 

over the TDA layer was the same as a control section 

underlain by conventional aggregate and soil. They 

also predicted that the tensile would be similar for as 

little as 457 mm (18 inches) of soil cover. Soil cover 

thicknesses between 0.5 and 1.2 m (20 and 47 inches) 

are recommended, depending on the traffic loading. 

The lower end of this range may be acceptable for 

applications with low truck traffic, such as parking 

lots and rural roads. However, the surface deflections 

under heavy vehicles immediately after the soil cover 

is placed will be noticeable, although it will decrease 

with additional traffic.

Guidelines to Limit Heating

Three thick TDA fills (greater than 7.9 m [26 feet] 

thick) have undergone a self-heating reaction. Two 

of these projects were located in Washington State, 

and one was in Colorado. These projects were 

constructed in 1995, and each experienced a serious 

self-heating reaction within 6 months after they 

had been completed (Ref. 17). The lessons learned 

from these projects were condensed into design 

guidelines developed by the Ad Hoc Civil Engineering 

Committee (Ref. 1), a partnership of government 

and industry that deals with reuse of scrap tires for 

civil engineering. The overall philosophy behind 

development of the guidelines was to minimize the 

presence of factors that could contribute to selfheating. The guidelines were subsequently published 

by ASTM International (then the American Society for 

Testing and Materials, Ref. 3) and distributed by the 

Federal Highway Administration. The guidelines are 

given in Appendix B. 
59

Chapter 5: Tire Derived Aggregate and Whole Tires for Civil Engineering Applications Scrap Tires:

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Highway Embankments Constructed on Weak 

Ground

The purpose of using TDA as lightweight fill for 

highway embankments constructed on weak, 

compressible soil is to increase global stability and 

reduce long-term settlement. There is no universal 

design for this application. However, most designs 

share the following features:

•	 Ingress of air and water is limited by a lowpermeability soil cover on the sides and top of 

the TDA zone. The low-permeability soil cover 

should be inorganic soil with a minimum of 30 

percent passing the No. 200 (0.075 mm) sieve. 

The thickness of the low-permeability soil layer 

typically ranges between 0.6 and 2 m (2 and 6 

feet).

•	 Geotextile that meets the requirements of

AASTHO M288, Class 2, is used to separate the 

TDA from the adjoining soil.

•	 The TDA is placed in 300-mm (12 inch)-thick

lifts, and each lift is compacted by six passes 

of compaction equipment with a minimum 

operating weight of 9.8 metric tons (10 U.S. tons). 

The compaction equipment may be a smooth 

drum vibratory roller, a tamping foot roller, or a 

bulldozer with conventional width tracks.

•	 The projects use Type B TDA (see Appendix B for

material specifications).

•	 The projects fully comply with the guidelines to

limit heating (Appendix B).

A typical cross section of a lightweight embankment 

fill project is given in Exhibit 5-6. The use of TDA 

for this application is illustrated further by two case 

histories given in Appendix E.

Fill Construction in the Mexico City Basin

Many of the populated areas of Mexico are 

underlain by volcanic lacustrine clay, including 

Mexico City (Ref. 52). The clay has a very porous 

structure because of the high content of 

microfossils and diatoms (Ref. 7). Engineering 

characteristics of this soil include a high liquid 

limit, water content in excess of the liquid 

limit, a high void ratio (up to e = 14), expansion 

when wetted, sensitivity to remolding, low 

shear strength, high compressibility, and high 

Exhibit 5-4. Plan view of Oregon tire shred field trial (Ref. 47)
60

Chapter 5: Tire Derived Aggregate and Whole Tires for Civil Engineering Applications Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

secondary compression (Refs. 7, 52). For instance, the 

thickness of the underlying volcanic lacustrine clay 

near the Palace of Fine Arts in Mexico City is 180 m 

(600 feet) (Ref. 48). One technique to overcome the 

challenges presented by this highly compressible soil 

would be to use TDA as lightweight fill to construct 

embankments and low-unit-weight backfill for walls. 

It is recommended that opportunities to use TDA in 

areas of the country underlain by volcanic lacustrine 

clay be vigorously pursued.

Landslide Stabilization

Landslides can have a significant impact on roads 

and other infrastructure. In cases where the head 

of a slide intersects a road, it may be possible to use 

TDA as lightweight fill to help stabilize the slide. The 

design principle is to excavate the soil off of the top 

of the slide and replace it with lightweight TDA fill 

to reduce the force driving the slide. In some cases, 

use of TDA as lightweight fill is combined with 

other techniques, including constructing a berm 

of soil or rock at the toe of the slide to increase 

the resisting force, changing the geometry of the 

slope to improve the stability, or adding drainage 

features to remove excess water from the base 

of the sliding mass. The use of TDA for landslide 

stabilization will be illustrated using a case history.

The case history is located on U.S. Route 42 

near Roseburg, Oregon (Ref. 47). As part of a 

project to improve the highway’s alignment, an 

embankment was raised and widened, which 

reactivated an old slide. The head of the slide 

was stabilized by using TDA as lightweight 

fill to reduce the driving force, placing a 

counterbalancing fill at the toe of the slide to increase 

the resisting force, and adding a drainage blanket to 

remove excess water. The project is shown in plan 

in Exhibit 5-4 and in cross section in Exhibit 5-5. The 

earthwork was done in 1990, and final paving was 

completed in 1991.

The specifications for this early project called for TDA 

with 80 percent passing the 200 mm (8-inch) size and 

50 percent larger than the 100-mm (4-inch) size; the 

maximum size measured in any direction was 610 

mm (24 inches). The specification for metal fragments 

was as follows: “All metal fragments were to be 

firmly attached and 98 percent embedded in the tire 

sections from which they are cut. No metal particles 

could be placed in the fill without being contained 

within a rubber segment. Ends of metal belts and 

beads were expected to be exposed only in the cut 

faces of some tire shreds.” Upton and Machan (Ref. 47) 

note that the TDA fill contained oversize pieces and 

excess metal fragments.

The TDA was placed in 1-m (3-feet) lifts and 

compacted with three passes of a Caterpillar D-8 

bulldozer. A Caterpillar D-6 bulldozer was also tried, 

but it appeared to be less effective than the D-8. Side 

slopes were trimmed with an excavator. The TDA was 

separated from the surrounding soil with a geotextile. 

The maximum thickness of TDA fill was about 4.3 m 

(14 feet). At one point during construction, a 2.4-

m (8-foot)-high vertical face of TDA was exposed 

and remained stable. After compaction, but before 

placement of the overlying soil cover, the TDA unit 

weight was estimated to be 0.72 Mg/m3

 (45 pcf). The 

overlying cover consisted of 0.91 m (36 inches) of soil, 

Exhibit. 5-5. Cross section through Oregon tire shreds field trail (Ref. 47)
61

Chapter 5: Tire Derived Aggregate and Whole Tires for Civil Engineering Applications Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

0.58 m (23 inches) of aggregate base course giving a 

total soil cover of 1.50 m (59 inches). The overlying 

pavement was 200-mm (8-inches) thick. After 

compression under the weight of overlying material, 

unit weight was estimated to be 0.85 Mg/m3 (53 pcf).

Wall Backfill

There are several advantages to using TDA as backfill 

behind walls, including reduction in horizontal 

stress, reduction in vertical stress on compressible 

foundation soils, and improved drainage. The design 

guidelines for use of TDA as wall backfill are largely 

derived from a full-scale test conducted at the 

University of Maine, as described in the following 

subsections (Refs. 44, 45).

Facility Design

The test facility is 4.88 m (16 feet) high and 4.47 m by 

4.57 m (14.7 feet by 15 feet) in plan. It consists of four 

walls and a reinforced concrete foundation. The two 

sidewalls are reinforced concrete. The back wall is 

removable, which allowed the backfill to be removed 

after a test had been completed. The front wall 

consists of three panels. Forces and pressures were 

measured on the center panel to reduce the influence 

of friction between the backfill and the sidewalls. 

The center panel was mounted on six load cells: two 

oriented vertically at the base of the panel to measure 

the shear force; and four oriented horizontally, two 

at the bottom of the panel and two at the top, to 

measure the horizontal force. The center panel also 

contained four pressure cells cast into its concrete 

face. Outward rotation of the three panels about their 

bases was controlled using screw jacks. Concrete 

blocks were used to apply surcharges up to 35.9 kPa 

(750 psf). The facility design is shown in Exhibits 5-6 

and 5-7. 

TDA Properties

TDA from three suppliers were tested. The TDA 

from Pine State and Palmer was long and flat with 

many exposed steel belts, while TDA from F&B was 

equi-dimensional with few exposed steel belts. 

The TDA was uniformly graded and composed 

primarily of gravel-size particles. Gradation of 

the TDA showed that F&B TDA was the smallest 

with a 38-mm (1.5-inches) maximum size, while 

the maximum size of both Pine State and Palmer 

TDA was 76-mm (3-inches). The TDA was placed 

in 200-mm (8-inch) lifts and compacted with 

four passes of a walk-behind vibratory tamping 

Exhibit 5-6. Plan and cross-section of full-scale retaining wall test facility 

10.11m

6.17

m

concrete

side walls 4.2

2

m

5.74m

a) PLAN VIEW

face of

front wall

4.57m

back wall

concrete

side walls 4.8

8

m

5.74m

b) CROSS-SECTION

foundation

0.51m

8.59m

4.57m

0.51m

overhead crane

4.7

2

m
62

Chapter 5: Tire Derived Aggregate and Whole Tires for Civil Engineering Applications Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

foot roller with a static weight of 1,180 kg (2,600 

pounds). The field density was measured by 

compacting a lift of tire shreds in a 3.05-m 

(10-foot)-long by 1.02-m (3.3-foot)-wide box. The 

average field density based on five tests was 0.71 

Mg/m3 (44.3 pcf) for F&B, 0.69 Mg/m3 (43.1 pcf) for 

Palmer, and 0.71 Mg/m3 (44.3 pcf) for Pine State.

Exhibit 5-7. Elevation and cross-section for front wall center panel 

Exhibit 5-8. At-rest stress distribution for Palmer shreds at four surcharges Exhibit 5-9. At-rest stress distribution at a 35.9 kPa surcharge 

compared with granular fill 

concrete face

pressure cell

pressure cells

0.51m bottom hinge

3.8

6

m

2.0

8

m

4.8

8

m

a) ELEVATION

bottom 

hinge vertical load cells

0.55m

1.47m

pressure

 cell

pressure

cells

horizontal load cell

b) CROSS-SECTION

vertical load cell

pressure cell

(cast into face)

horizontal load cell

Section A - A'

A A'

0.0 4.0 8.0 12.0 16.0 20.0

Horizontal stress (kPa)

0.00

1.00

2.00

3.00

4.00

5.00

Elevation (m)

no surcharge

12.0 kPa

23.9 kPa

35.9 kPa

1 m = 3.28 ft, 1 kPa = 20.89 psf

0.0 10.0 20.0 30.0 40.0 50.0

Horizontal stress (kPa)

0.00

1.00

2.00

3.00

4.00

5.00

Elevation (m)

granular fill (typical)

Pine State Recycling

Palmer Shredding

F & B Enterprises

1 m = 3.28 ft, 1 kPa = 20.89 psf
63

Chapter 5: Tire Derived Aggregate and Whole Tires for Civil Engineering Applications Scrap Tires:

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At-Rest Horizontal Pressure

The horizontal stress distribution was calculated using 

the load cell measurements by summing the moment 

forces about the base of the panel and assuming the 

distribution to be trapezoidal. The horizontal stress 

distributions for each of the suppliers were similar. A 

typical plot with Palmer TDA is shown on Exhibit 5-8. 

This exhibit shows that the horizontal stress increases 

with increasing surcharge. At the lower surcharges, 

the horizontal stress increases with depth, but the 

horizontal stresses becomes almost constant with 

depth at the higher surcharges.

The horizontal stress distributions of tire shreds and 

granular fill under the 35.9 kPa (750 psf) surcharge 

were compared. As part of the study, a granular fill 

was tested in the facility. However, the granular fill 

was well-graded gravelly sand. It was placed near 

optimum water content and therefore exhibited 

considerable apparent cohesion. This cohesion was 

evidenced by the granular fill standing on a 4.57-m 

(15-foot)-high vertical face when the back wall was 

removed. The apparent cohesion led to unrealistic 

values of horizontal stress. Therefore, the horizontal 

stress distributions at the 35.9 kPa (750 psf) surcharge 

for each of the tire shred suppliers were compared 

with the expected horizontal stress distribution 

for a typical granular fill with a compacted density 

of 2.02 Mg/m3

 (126 pcf) and a coefficient of lateral 

earth pressure at rest (Ko) of 0.38, as shown in Exhibit 

5-9. The resultant of the horizontal stress from the 

tire shreds is approximately 45 percent less than for 

granular fill. This difference is a result, at least in part, 

of the density of tire shreds, which is one-third to 

one-half of conventional granular backfill.

The coefficient of lateral earth pressure at rest for 

TDA was calculated. For no surcharge, Ko was 

calculated just below the fill surface because the 

vertical stress is zero at the fill surface, so Ko is 

undefined. The values for Ko are summarized 

in Table 5-2, which shows that the coefficient 

of lateral earth pressure at rest decreases with 

depth for all four loading conditions. The values 

for Ko also decrease from no surcharge to 23.9 

kPa (500 psf). Ko then remained approximately 

constant from 23.9 to 35.9 kPa (500 to 750 psf). 

The differences between Ko for each supplier at a 

given surcharge and depth are small. Comparison 

of Ko for TDA shown on Table 5-2 with typical Ko of 

normally consolidated granular soils of 0.35 to 0.50 

(Ref. 14) shows Ko for TDA is lower at the 2.0 m (6.6 

feet) and 4.0 m (13.1 feet) depths. This comparison 

also suggests that the lower at-rest pressures 

produced by TDA are a result of both their lower Ko 

and their lower density.

Active Earth Pressure

After measurements for the at-rest condition 

were completed, the wall was rotated outward to 

achieve active earth pressures. The horizontal stress 

distributions for all of the suppliers at the same 

wall rotation were similar. The horizontal stress 

distributions immediately after each wall rotation for 

Palmer TDA under an applied surcharge of 35.9 kPa 

(750 psf) are shown in Exhibit 5-10. Before rotation, 

Table 5-2. Coefficient of Lateral Earth Pressure at Rest, Ko

Surcharge

Supplier Depth (m) 0 12.0 kPa 23.9 kPa 35.9 kPa

F&B Enterprises

0 0.99a 0.51 0.44 0.45

2 0.39 0.33 0.32 0.32

4 0.31 0.28 0.26 0.25

Palmer Shredding

0 0.94a 0.58 0.51 0.51

2 0.37 0.33 0.27 0.33

4 0.29 0.27 0.17 0.24

Pine State 

Recycling

0 0.93a 0.55 0.46 0.47

2 0.37 0.32 0.32 0.32

4 0.28 0.26 0.26 0.25

Average

0 0.95a 0.55 0.47b 0.47b

2 0.38 0.33 0.31b 0.31b

4 0.29 0.27 0.24b 0.24b

a

 Value found at a depth of 0.5 m (1.6 feet)

b

 Average from 23.9 kPa (500 psf) and 35.9 kPa (750 psf) surcharges
64

Chapter 5: Tire Derived Aggregate and Whole Tires for Civil Engineering Applications Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

the horizontal stress decreases slightly with depth; 

then, as the wall is rotated from at-rest conditions 

to 0.01H (H is the rotation factor as a function of 

the wall height), the horizontal stress decreases 

significantly at the top. At a rotation of 0.01H, 

the magnitude of the resultant horizontal force 

was 50 percent less than before rotation. Similar 

decreases in horizontal stress were measured for 

F&B and Pine State. The horizontal stress for TDA 

at a rotation of 0.01H was compared with a typical 

granular fill with a compacted density (ρ) of 2.02 

Mg/m3

 (126 pcf) and a coefficient of lateral earth 

pressure at rest (Ka) of 0.24, as shown in Exhibit 

5-11. The resultant horizontal force from the TDA 

was approximately 35 percent less than that of the 

granular fill.

The earth pressure coefficient, K, was calculated for 

each TDA supplier at the 0.01H rotation and the larger 

rotations for Palmer and Pine State at depths of 0 m, 

2.0 m, and 4.0 m. The results are shown in Table 5-3. It 

is seen that for a rotation of 0.01H, K is similar for the 

three suppliers at each depth, with values ranging 

from 0.22 to 0.25 kPa. At larger rotations, K ranges 

from 0.16 to 0.18 kPa at a rotation of 0.03H for Palmer 

and from 0.08 to 0.12 kPa at a rotation of 0.04H for 

Pine State. These values suggest that K decreases 

with outward movement. Exhibit 5-12 shows that the 

effect of wall rotation on K is greater at the shallower 

depths. Moreover, reduction in K is small for rotations 

greater than 0.01H, suggesting that the reported K 

values were approaching the minimum values that 

meet the definition of active conditions. A reasonable 

approach for design would be to use the K for a 

rotation of 0.01H. Thus, a design K of 0.25 kPa would 

Exhibit 5-10. Stress distribution for Palmer shreds for 

wall rotations of zero to 0.01H

Exhibit 5-11. Stress at 35.9 kPa surcharge and 0.01H rotation 

compared with granular

0.0 4.0 8.0 12.0 16.0 20.0

Horizontal stress (kPa)

Elevation (m)

0.00

1.00

2.00

3.00

4.00

5.00

before rotation

0.001H, initial

0.005H, initial

0.01H, initial

0.0 5.0 10.0 15.0 20.0 25.0 30.0

Horizontal stress (kPa)

0.00

1.00

2.00

3.00

4.00

5.00

Elevation (m)

granular fill (typical)

F&B Enterprises, 0.01H (initial + 11 days)

Palmer Shredding, 0.01H (initial + 1 day)

Pine State Recycling, 0.01H (initial + 2 days)

Table 5-3. Earth Pressure Coefficient, K for Rotated Case

Supplier Depth (m)

Rotation

0.01H 0.03H 0.04H

F&B Enterprises

0 0.23 - - - -

2 0.23 - - - -

4 0.23 - - - -

Palmer Shredding

0 0.23 0.18 - -

2 0.22 0.17 - -

4 0.22 0.16 - -

Pine State Recycling

0 0.25 - - 0.08

2 0.23 - - 0.11

4 0.22 - - 0.12
65

Chapter 5: Tire Derived Aggregate and Whole Tires for Civil Engineering Applications Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

be reasonable and slightly conservative compared the 

values in Table 5 for conditions similar to this trial.

A simplified design approach was developed based 

on equivalent fluid pressure. The semiempirical 

design parameters were developed following the 

methods presented in Terzaghi and others (Ref. 42) for 

soils. The key parameter is a semi-empirical value, kh, 

with units of weight per unit volume. The method can 

be thought of as replacing the backfill with a fluid of 

density kh. The value kh can then be used to calculate 

the horizontal stress using:

σh = gkhd (Eq. 1)

where g is gravity, 9.81 meters/second2 (m/s2

), and d 

is the depth of the fill, as shown on Exhibit 5-13a. In 

cases where a surcharge is applied and the surface of 

the backfill is horizontal, the horizontal stress at any 

depth is increased by the amount:

pq

 = Cq (Eq. 2)

where C is a coefficient dependent on the backfill 

type, and q is the surcharge in units of load per unit 

area. The combination of the stress caused by the 

backfill and the surcharge results in a trapezoidal 

Exhibit 5-12. Effect of rotation on earth pressure coefficient at 35.9 kPa 

(750 psf) surcharge 

Exhibit 5-13. Semiemperical design procedure 

0.00 0.01 0.02 0.03

Rotation (xH)

0.10

0.20

0.30

0.40

0.50

0.60

Earth pressure coefficient, K

DEPTH

0 meters

2 meters

4 meters

top

center panel

surcharge 



d 

c)

khd

a) 

fill surface

d

tire shreds 

bottom

pq

khd pq +

b) 

surcharge, q

Separation of Eect of Surcharge

and Tire Shreds.

No Surcharge With Surcharge

Table 5-4. Semiempirical Design Parameters 

for Rotation of 0.01H

Supplier kh (mg/m3) C

F&B Enterprises 0.19 0.22

Palmer 

Shredding 0.18 0.23

Pine State 

Recycling 0.17 0.25
66

Chapter 5: Tire Derived Aggregate and Whole Tires for Civil Engineering Applications Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

distribution, as shown on Exhibit 5-13b. The values 

kh and C were found by dividing the trapezoid 

distributions determined from the load cells into two 

parts, as shown on Exhibit 5-13c. The contribution to 

the horizontal stress from the tire shreds was taken to 

be the triangular portion of the distribution, shown 

as σtire shreds. The remainder of the horizontal stress 

was assigned to the σsurcharge. The results for a rotation 

of 0.01H are shown in Table 5-4. It would be 

reasonable to use a kh = 0.18 Mg/m3

 (11 pcf) and 

C = 0.23 for design for conditions similar to this 

study. For comparison, the kh for granular backfill 

is about 0.5 Mg/m3 (31 pcf) (Ref. 42).

WHOLE TIRES FOR WALL 

CONSTRUCTION

Whole tires can be used to construct low retaining 

walls (Refs. 6, 35, 39, 50), along slopes as an erosion 

control method, or in wetland retention design. 

One system of wall construction proposed by the 

California Department of Transportation is shown 

in Exhibit 5-14 (Ref. 6), although there are many other 

methods of construction in use today. The tires are 

filled with compacted soil and in each given layer 

are hooked together with metal clips made from 

bent rebar. The adjoining layers are then connected 

by driving recycled metal delineator posts within 

the compacted soil. Erosion is of great concern for 

much of northern Mexico, as its arid climate does not 

Sample retaining wall using whole tires

Photo courtesy of La Comisión Estatal de Servicios Públicos de Tecate 

Whole tire wall used to impede soil erosion

Photo courtesy of La Comisión Estatal de Servicios Públicos de Tecate 

Example of the erosion that is possible with the 

conditions in Northern Mexico

Photo courtesy of La Comisión Estatal de Servicios Públicos de Tecate 

The Use of Scrap Tires as a Method 

of Erosion Control in Mexico

One study completed by El Instituto Tecnológico 

y de Estudios Superiores de Monterrey tested 

the efficiency of scrap tires used along slopes 

with poor growing conditions where erosion is 

a problem. In measuring sediment eroded for 

slopes both with and with out scrap tires they 

found in 82 percent reduction in erosion along 

the slopes that used the proposed system of 

scrap tires strung down the slope. The tires 

were also found to help retain moisture and aid 

in vegetative growth along the slope, further 

decreasing erosion. Wild grass was observed 

growing in 85 percent tire zone test areas 

compared with 10 percent growth in other 

areas. The institute concluded that there was 

no evidence of an increase in mosquitoes in 

the area caused by the use of tires, there was 

an overall decrease in maintenance costs and 

closures of slope areas as a result erosion, and 

at the time of the study (2006) the total system 

could be implemented for about $11.6 pesos 

(U.S. $0.90) per tire. For further information, 

contact Dr. Martin H. Bremer, Profesor 

Investigador en Sistemas Geoambientales at 

mbremer@itesm.mx. 
67

Chapter 5: Tire Derived Aggregate and Whole Tires for Civil Engineering Applications Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

readily support vegetative growth and the elevated 

landscapes create optimal conditions for erosion. 

Erosion in densely population areas can be dangerous 

and expensive to control. It can cause closure of 

and increased maintenance on roadways and affect 

housing built on or near eroding slopes. The use of 

scrap tires has been shown to be effective in the area 

of erosion control and can provide a low-cost solution 

for reuse of the scrap tires in the area. 

REFERENCES

1. Ad Hoc Civil Engineering Committee. 1997. 

“Design Guidelines to Minimize Internal Heating 

of Tire Shred Fills.” Scrap Tire Management 

Council, Washington, DC. 4 pp.

2. Ahmed, I. 1993. “Laboratory Study on Properties 

of Rubber Soils,” Report No. FHWA/IN/JHRP-93/4, 

School of Civil Engineering, Purdue University, 

West Lafayette, Indiana.

3. ASTM International. 1998. “Standard 

Practice for Use of Scrap Tires in Civil 

Engineering Applications.” ASTM D6270-98, 

ASTM International. W. Conshohocken, 

Pennsylvania.

4. Bosscher, P.J., Edil, T.B., and Eldin, N.N. 1993. 

“Construction and Performance of a Shredded 

Waste Tire Test Embankment.” Transportation 

Research Record 1345, Transportation 

Research Board, Washington, D.C., pp. 44-52.

5. Brophy, M. and Graney, J. 2004. “Groundwater 

Effects from Highway Tire Shred Use.” 

Environmental Forensics, Vol. 5, No. 2, June 

2004, pp. 79-84.

6. Caltrans. 1988. “The Use of Discarded Tires 

in Highway Maintenance.” Translab Design 

Information Brochure No. Tl/REC/1/88, California 

Department of Transportation, Sacramento, 

California.

7. Day, R.W. 2006. Foundation Engineering 

Handbook, McGraw-Hill, New York. p. 7.30.

8. Dickson, T.H., Dwyer, D.F., and Humphrey, D.N. 

2001. “Prototype Tire Shred Embankment 

Exhibit 5-14. Retaining wall system constructed from whole tires (Ref. 6)
68

Chapter 5: Tire Derived Aggregate and Whole Tires for Civil Engineering Applications Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

Construction by the New York State Department 

of Transportation.” Transportation Research 

Record No. 1755, Transportation Research Board, 

Washington, D.C. pp. 160-167.

9. Eldin, N.N. and Senouci, A.B. 1992. “Use of 

Scrap Tires in Road Construction.” Journal of 

Construction Engineering and Management, Vol. 

118, No. 3. September. pp. 561-576.

10. Exponent. 2003. “Tire Shred Leachate Study: 

Chemical Composition and Aquatic Toxicity for 

Above- and Below-Water-Table Applications.” 

Exponent, Oakland, California. 26 pp. + 

Appendices.

11. GeoSyntec. 1998a. “Guidance Manual - Tire 

Shreds as Cover Foundation, Leachate Drainage, 

and Operations Layer Material at Municipal 

Solid Waste Landfills.” Prepared for California 

Integrated Waste Management Board.

12. GeoSyntec. 1998b. “Tire Shreds as Leachate 

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13. GeoSyntec. 1998c. “Guidance Manual – 

Shredded Tires as Gas Collection Material at 

Municipal Solid Waste Landfills.” Prepared for 

California Integrated Waste Management Board.

14. Holtz, R.D., and Kovacs, W.D. 1981. An 

Introduction to Geotechnical Engineering. 

Prentice-Hall, Englewood Cliffs, New Jersey. 733 

pp.

15. Hoppe, E.J. 1998. “Field Study of ShreddedTire Embankment.” Transportation Research 

Record No. 1619. Transportation Research Board, 

Washington, D.C. pp. 47-54.

16. Hoppe, E.J. and Mullen, W.G. 2004. “Field 

Study of a Shredded-Tire Embankment in Virginia 

– Final Report.” Report No. VTRC 04-R20. Virginia 

Transportation Research Council, Charlottesvile, 

Virginia. 52 pp.

17. Humphrey, D.N. 1996. “Investigation of 

Exothermic Reaction in Tire Shred Fill Located on 

SR 100 in Ilwaco, Washington.” Prepared for the 

Federal Highways Administration, Washington, 

D.C. 60 pp.

18. Humphrey, D.N. 2004. “Effectiveness of Design 

Guidelines for use of Tire Derived Aggregate 

as Lightweight Embankment Fill.” Recycled 

Materials in Geotechnics. ASCE, pp. 61-74.

19. Humphrey, D.N . 2008. “Tire Derived Aggregate 

as Lightweight Fill for Embankments and 

Retaining Walls.” Proceedings of the International 

Workshop on Scrap Tire Derived Geomaterials – 

Opportunities and Challenges, IW-TDGM 2007. 

Taylor and Francis/Balkema, Netherlands. pp. 

59-81.

20. Humphrey, D.N., and Eaton, R.A. 1995. “Field 

Performance of Tire Chips as Subgrade Insulation 

for Rural Roads.” Proceedings of the Sixth 

International Conference on Low-Volume Roads, 

Transportation Research Board, Washington, D.C. 

Vol. 2, pp. 77-86.

21. Humphrey, D.N., and Katz, L.E. 1995. “Water 

Quality Testing for Dingley Road Tire Chip Test 

Project.” A report for the Town of Richmond, 

Maine, by Department of Civil and Environmental 

Engineering, University of Maine, Orono, Maine. 

35 pp.

22. Humphrey, D.N., and Katz, L.E. 2000. “Five-Year 

Field Study of the Effect of Tire shreds Placed 

above the Water Table on Groundwater Quality.” 

Transportation Research Record No. 1714, 

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pp. 18-24.

23. Humphrey, D.N., and Katz, L.E. 2001. “Field 

Study of the Water Quality Effects of Tire Shreds 

Placed Below the Water Table.” Proceedings 

of the International Conference on Beneficial 

Use of Recycled Materials in Transportation 

Applications, November 13, Arlington, VA, pp. 

699-708.

24. Humphrey, D.N. and Manion, W.P. 1992. 

“Properties of Tire Chips for Lightweight Fill.” 

Proceedings of Grouting, Soil Improvement, and 

Geosynthetics, New Orleans, Louisiana, Vol. 2, pp. 

1344-1355.

25 Humphrey, D.N., and Nickels, W.L., Jr. 1997. 

“Effect of Tire Chips as Lightweight Fill on 

Pavement Performance.” Proceedings of the 

Fourteenth International Conference on Soil 

Mechanics and Foundation Engineering, Vol. 3, 

pp. 1617-1620.

26. Humphrey, D.N., and Swett, M. 2006. Literature 

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Derived Aggreagate and Rubber Modified 

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27. Humphrey, D.N., Whetten, N., Weaver, J., Recker, 

K., and Cosgrove, T.A. 1998. “Tire TDA as 

Lightweight Fill for Embankments and Retaining 

Walls.” Proceedings of the Conference on 

Recycled Materials in Geotechnical Applications, 

C. Vipulanandan and D. Elton, eds., ASCE, pp. 51-

65.

28. Humphrey, D.N., Whetten, N., Weaver, J., and 

Recker, K. 2000. “Tire TDA as Lightweight Fill for 

Construction on Weak Marine Clay.” Proceedings 

of the International Symposium on Coastal 

Geotechnical Engineering in Practice, Balkema, 

Rotterdam, pp. 611-616.

29. Jeremic, B., Putnam, J., Kallol, S. Humphrey, 

D., and Patenaude, S. 2004. “Calibration of 

Elastic-Plastic Material Model for Tire Shreds.” 

Geotechnical Engineering for Transportation 

Projects: Proceedings of Geo-Trans 2004, ASCE, 

pp. 760-767.

30. Jesionek, K.S., Humphrey, D.N., and Dunn, R.J. 

1998. “Overview of Shredded Tire Applications 

in Landfills.” Proceedings of the Tire Industry 

Conference, Clemson University, March 4-6. 12 p.

31. Koerner, J.R.., Soong T.-Y., and Koerner, R.M. 1998. 

“A Survey of Solid Waste Landfill Liner and Cover 

Systems: Part 1—USA States.” GRI Report #21, GSI, 

Folsom, PA, 211 pp.

32. Lawrence, B.K., Chen, L.H., and Humphrey, 

D.N. 1998. “Use of Tire Chip/Soil Mixtures to 

Limit Frost Heave and Pavement Damage of 

Paved Roads.” A Study for the New England 

Transportation Consortium, by Department of 

Civil and Environmental Engineering, University 

of Maine, Orono, Maine, 316 pp.

33. Manion, W.P., and Humphrey, D.N. 1992. “Use 

of Tire Chips as Lightweight and Conventional 

Embankment Fill, Phase I - Laboratory.” Technical 

Paper 91-1, Technical Services Division, Maine 

Department of Transportation, Augusta, Maine.

34. Nickels, W.L., Jr. 1995. “The Effect of Tire Chips 

as Subgrade Fill on Paved Roads.” M.S. Thesis, 

Department of Civil Engineering, University of 

Maine, Orono, Maine, 215 pp.

35. Nguyen, M.X. and Williams, J.A. 1989. 

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Tires in Highway Maintenance.” Report No. CA/

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36. Qian, X., Koerner, R.M., and Gray, D.H. 2002. 

Geotechnical Aspects of Landfill Design and 

Construction. Prentice Hall, Upper Saddle River, 

New Jersey. 717 pp.

37. Recycling Research Institute. 2005. “Scrap 

Tire and Rubber Users Directory.” 14th Edition, 

Recycling Research Institute, Leesburg, Virginia. 

150 pp.

38. Reid, R.A., and Soupir, S.P. 1998. “Mitigation of 

Void Development Under Bridge Approach 

Slabs Using Rubber Tire Chips.” Proceedings 

of the Conference on Recycled Materials in 

Geotechnical Applications. ASCE, pp. 37-50. 

39. Richmond, R.L., and Jackura, K.A. 1984. “Field 

Performance of Experimental Tire Anchor 

Timber Wall.” Report No. FHWA/CA/TL-84/16, 

Office of Transportation Laboratory, California 

Dept. of Transportation, Sacramento, 

California.

40. Sheehan, P.J., Warmerdam, J.M., Ogle, S., 

Humphrey, D.N., and Patenaude, S.M. 2006. 

“Evaluating the Toxicity of Leachate from Tire 

Shred Fill in Roads and the Risk to Aquatic 

Ecosystems.” Journal of Environmental 

Toxicology and Chemistry. Vol. 25, No. 2, pp. 

400-411.

41. Tanchaisawat, T., Bergado, D.T., and 

Voottipruex, P. 2008. “Numerical Simulation 

and Sensitivity Analyses of Full-Scale Test 

Embankment with Reinforced Lightweight 

Geomaterials on Soft Bangkok Clay.” 

Geotextiles and Geomembranes, Vol. 26, No. 6. 

pp. 498-511.

42. Terzaghi, K., Peck, R.B. and Mesri, G. 1996. Soil 

Mechanics in Engineering Practice. 3rd ed. 

John Wiley & Sons, Inc., New York.

43. Tandon, V., Velazco, D.A., Nazarian, S., and 

Picornell, M. 2007. “Performance Monitoring of 

Embankments Containing Tire Chips: Case Study.” 

Journal of Performance of Constructed Facilities, 

Vol. 21, No. 3. pp. 207-214.

44. Tweedie, J.J., Humphrey, D.N., and Sandford, 

T.C. 1998a. “Full Scale Field Trials of Tire TDA 

as Lightweight Retaining Wall Backfill, At-Rest 
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Management for the U.S. and Mexico

Conditions.” Transportation Research Record No. 

1619. TRB, Washington, D.C. pp. 64-71.

45. Tweedie, J.J., Humphrey, D.N., and Sandford, 

T.C. 1998b. “Tire TDA as Retaining Wall Backfill, 

Active Conditions.” Journal of Geotechnical and 

Geoenvironmental Engineering. ASCE, Vol. 124, 

No. 11. pp. 1061-1070.

46. Tweedie, J.J., Humphrey, D.N., Wight, M.H., 

Shaw, D.E., and Stetson, J.H. 2004. “Old Town 

– Mud Point Inlet Bridge, Rehabilitation of a 

Timber Structure with Tire TDA.” Geotechnical 

Engineering for Transportation Projects: 

Proceedings of Geo-Trans 2004. ASCE. pp. 740-

749.

47. Upton, R.J., and Machan, G. 1993. “Use 

of Shredded Tires for Lightweight Fill.” 

Transportation Research Record No. 1422. TRB, 

Washington, D.C. pp. 36-45.

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In: Foundation Engineering, G.A. Leonards, Ed., 

McGraw-Hill, New York. pp. 826 to 893.

49. Whetten, N., Weaver, J. Humphrey, D., and 

Sandford, T. 1997. “Rubber Meets the Road 

in Maine.” Civil Engineering, Vol. 67, No. 9. 

September. pp. 60-63.

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FHWA/CA/TL-87/07. Office of Transportation 

Laboratory, California Department of 

Transportation, Sacramento, California.

51. Wolfe, S.L., Humphrey, D.N., and Wetzel, 

E.A. 2004. “Development of Tire Shred 

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New York, pp. 1-65.
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CHAPTER 6

Transportation and Processing Economics

The preceding chapters focused on major 

applications, or specialized uses, for scrap tire 

resources because markets define the required 

collection and processing methods. Collection can be 

local for small, nearby markets, or regional, for large 

markets and centralized processing facilities. Scrap 

tires can be used whole or processed into pieces 

ranging from large civil engineering chips to fine 

crumb rubber, with differing processing requirements 

for each size. Collection and processing systems 

naturally evolve with markets, but the probability of 

succeeding with limited resources is maximized by 

targeting defined initial market needs. The following 

section provides a brief discussion of basic collection, 

transportation, and processing (including methods, 

equipment, processes, and economics) to assist in 

evaluating alternatives. The discussion is based on 

historical experience in the United States, but U.S. 

economics have been converted into comparable 

Mexican economics to make them more applicable 

to the projected market and economic structure 

in Mexico and increase their usefulness in Mexico. 

This section is based on 2008 costs and may vary 

depending on present market values.

COLLECTION AND TRANSPORTATION

Scrap tire collecting and hauling are critical 

components in effective use of the tire resource. 

The impact of efficient collection on the economic 

viability of scrap tire management alternatives 

is often underestimated. Hauling, on the other 

hand, will evolve with the management program. 

If no regulations or enforcement exist to govern 

tire disposal, transportation costs will encourage 

discarding them at the closest site, especially for 

small collection vehicles such as pickup trucks. Small 

vehicles generally represent the highest risk for illegal 

tire disposal in the United States. However, once 

regulations are in place and enforced, competitive 

pressure will force the use of efficient collection 

methods and vehicles. Inefficient haulers will fail.

Methods

Scrap tires are normally generated where 

replacement tires are installed, such as at tire stores, 

car dealerships, and repair shops. Tires are a naturally 

segregated waste stream unless they are mixed with 

other wastes intentionally. In the United States, 

they are generally collected separately, without 

contamination from other materials, by people or 

companies that specialize in tire collection. Reusable 

casings are removed for resale, and the rest are 

properly disposed of at processing facilities or 

landfills if appropriate regulations, penalties, and 

enforcement are in place. Otherwise, the remaining 

tires are too often dumped or stockpiled because 

these disposal options are the lowest cost.

Tires can be collected on scheduled intervals or 

an as-needed basis. Route collection generally 

involves trucks travelling scheduled routes at 

designated frequency, with tires loaded by the 

driver, an assistant, or store personnel. Tires are 

counted during loading for invoicing. Collection 

can be requested as needed rather than on a 

regular schedule for stores with small or variable 

generation. Charges for this type of pickup are 

generally based on the number of tires, distance, 

and other factors.

 Trailers are often parked at stores with high 

volumes and adequate space. The trailers are 

loaded by store employees and locked to prevent 

vandalism, dumping, and arson. When the trailer 

is full, the store notifies the collector and an 

empty trailer is delivered at the same time that 

the full trailer is removed. The store is generally 

charged a fixed fee per trailer based on distance, 

turnover frequency, gradable casings, and other 

cost-sensitive factors. Dumpsters and bins have 

also been used, but limited capacity and inefficient 

hauling make these alternatives expensive. In 

all cases, the hauler is paid by the store or by the 

government to haul the tires to an acceptable 

disposal site based on the requirements of the waste 

tire program that is used in the area.

Equipment

A wide variety of vehicles have been used to haul 

tires, anything from wheelbarrows to diesel tractors. 

The following is a brief discussion of some commonly 

used vehicle types.

Pickup Truck

Pickup trucks are a common vehicle capable of 

hauling many materials, including scrap tires. 

Carrying capacity for full-size pickups ranges from 
72

Chapter 6: Transportation and Processing Economics Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

about 450 to 900 kg (1,000 to 2,000 pounds), 

depending on model and condition. The bed 

can hold the equivalent of up to 50 passenger 

tires (10 medium truck tires) if properly laced or 

stacked. These tires weigh approximately 1,000 

pounds, the normal carrying capacity of basic 

half-ton (sometimes called 150-class) pickups in 

good condition. A metal cage can be added to 

increase the containment volume if the pickup 

has sufficient load carrying capacity. Some 0.7 

metric ton and 0.9 metric ton (called 250- and 

350-Class) pickups can carry 900 kg (2,000 

pounds) or more. A caged trailer can be used to 

optimize hauling capacity because most pickups 

can tow more weight than they can carry within 

the truck itself. Towing capacity generally ranges 

from 2,250 to 4,550 kg (5,000 to 10,000 pounds), 

representing 250 to 500 passenger tires. Since 

most manageable trailers cannot hold that number 

of tires, trailer volume generally controls towing 

capacity.

Box Truck

Box trucks are commonly used for local waste tire 

collections. They can hold up to 400 passenger tires 

if tightly laced. Examples of a box truck and proper 

lacing techniques are shown in the photos to the 

right. 

The driver typically travels a designated route, 

stopping to load tires from regular customers or those 

requesting service from a dispatcher. Infrequently, 

cargo vans or an open cage welded onto a flatbed 

truck have been used as alternatives. 

Tractor Trailer

Traditional tractor trailer rigs are commonly used 

for collection and transport of large volumes of 

tires. Capacity for whole tires is limited by volume 

and depends on the trailer size, tire types, loading 

methods, and contamination. It ranges from 500 

to 750 tires in a 27-foot tandem trailer to more than 

1,500 stacked in laced fashion in a 52-foot trailer. 

Processing reduces the tire volume by a factor of two 

to five, so processed tire loads are normally limited 

by maximum weight allowances, and not volume. 

Normal payload limits are 22 to 26 U.S. tons (2,200 

to 2,600 passenger tire equivalents) in the United 

States, based on total weight limits minus the weight 

of the tractor and empty trailer. Tandem trailers 

further increase tire capacity for long hauls when local 

regulations allow them.

Collection/Hauling Economics

Tires can be collected and hauled by whatever vehicle 

is available, but experience and the competitive 

nature of the business have led good operators to 

carefully evaluate optimum equipment for specific 

purposes. To illustrate the differences, capital 

and operating costs associated with collecting 

and hauling tires about 30,000 miles a year were 

calculated for each major type of equipment. Since 

all of these costs vary significantly with time and 

location, this information should be used only for 

comparison or as a basis for recalculation using 

local economic conditions. The example assumes 

the purchase of used equipment in good condition 

with estimated labor, maintenance, and fuel costs 

based on some areas in the United States. Estimated 

insurance, depreciation, and a 20-percent annual 

return on investment have been included in the fixed 

cost calculations, but interest was not included for 

any funds borrowed. The initial U.S.-based economics 

are included in Appendix H for reference by those in 

border areas. In addition, a Spanish version of these 

Box truck for tire transportation 

Photo courtesy of Tire Recycling and Disposal, Inc. 

Proper lacing technique for tire transportation

Photo courtesy of Tire Recycling and Disposal, Inc. 
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Chapter 6: Transportation and Processing Economics Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

economics adjusted to reflect economics within 

Mexico is also included in Appendix H.

The capital and operating costs were estimated for 

a pickup truck, a pickup with a caged trailer, a box 

truck, and a diesel tractor with a 48-foot trailer. For 

simplicity, it was assumed that the vehicle averages 

48.28 km/hour (30 mph), allowing time for tire 

loading along the way. The costs were calculated on 

a cost/km basis, and then reduced to cost/km/tire to 

more accurately reflect volume economics. The data 

is provided in Appendix F at the end of this chapter. 

Exhibit 6-1 summarizes the capital and operating 

costs ($/mile) for each of these alternatives. As 

expected, both costs increase with size of the vehicle. 

However, cost/km/tire is a better indicator of hauling 

efficiency than is cost/mile. Exhibit 6-2 provides 

the cost/tire for hauls of 25, 100, and 500 miles for 

comparison, again based on the data shown in 

Appendix F. Pickup trucks are expensive on a cost/

tire basis even on short hauls, but become prohibitive 

on longer trips. A caged trailer improves capacity and 

efficiency, but practical service range is generally 100 

to 150 miles. Box trucks are slightly more efficient, 

but are normally used for total travel distances of less 

than 200 miles. Tractor trailers are the most efficient 

choice for longer distances. Longer trailers (52 feet) or 

tandem 27-foot trailers are most efficient if roads and 

regulations allow them. 

These calculations also assume that the vehicle is 

filled up during the trip. The cost/tire will increase if 

it is not filled, so a smaller vehicle may be better in 

these cases. In some cases, it may be most efficient 

to establish a collection point in a town or area where 

tires can be accumulated and then be hauled in larger 

vehicles to regional processing facilities or markets.

PROCESSING

Tires must withstand impact and high speeds while 

on vehicles, and they have to do so at temperatures 

ranging from subzero to desert heat. The flexibility of 

rubber, combined with the strength and abrasiveness 

of reinforcing steel, makes tires a challenge to process 

for product applications. The following section 

discusses basic tire processing and economics as a 

generic framework for individual evaluations. 

Scrap tire processing covers a broad range of 

methods and equipment. This discussion focuses on 

large markets that can use whole tires and shredded 

tires ranging from large Type B TDA (See Chapter 3 for 

discussion of Type B TDA) to nominal 2.5-cm (1-inch) 

TDF (discussed in the Energy Utilization Section) and 

the equipment commonly used to produce these 

products. Additional equipment that can be added 

to further reduce product size for ground rubber 

applications is also discussed. Capital and operating 

costs associated with this additional equipment are 

substantial. 

Critical Issues

Many U.S. scrap tire processors, and especially ground 

rubber producers, have historically failed within 1 to 

5 years after they enter the business. Many of the 

failures may have been avoided by considering the 

following issues before any investment decisions 

were made:

Product Markets

The rate of market development for scrap tire 

products has historically limited the growth 

of tire processing. Elapsed time and costs 

associated with market development are generally 

underestimated and have a major impact on 

the economic viability of processors. The time 

required to develop markets can be years, not 

weeks, and may require customer identification 

and acceptance, regulatory approval, product 

testing, market introduction, and distribution 

development. Accumulating product inventory 

while markets develop is doubly expensive 

because it decreases revenue anticipated from 

product sales while increasing working capital 

requirements. The combined result can lead to 

failure of an otherwise well-conceived operation 

because, sooner or later, either financial resources 

or regulatory agencies will limit the inventory of 

products and tires at a processing site.

Product Specifications

Time spent defining product specifications and 

processing requirements before investment 

decisions generally saves money in implementation 

and minimizes subsequent, expensive changes. 

Equipment that may be appropriate for one 

application can be technically or economically 

unsuitable for another. Considering the evolutionary 

stages for markets and products can improve the 

probability that initial equipment purchases will 

have the flexibility to serve future needs. Properly 

evaluating product volumes, specifications, and 

timing are probably the most critical, and commonly 

ignored, steps in establishing a successful processing 

operation. 

Product Pricing

Apparent scrap tire product pricing may be lower in 

practice for these important reasons:
74

Chapter 6: Transportation and Processing Economics Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

1 Mile Haul

25 Mile Haul

100 Mile Haul

200 Mile Haul

500 Mile Haul

$0.00 $1.00 $2.00 $3.00 $4.00 $5.00 $6.00 $7.00 $8.00$9.00

Total Cost/Mile/Tire

Tractor with 48 foot trailer

(1,400 tire capacity)

Box truck

(400 tire capacity)

Pickup with trailer

(250 tire capacity)

Pickup truck

(50 tire capacity)

Labor

Fuel

Maintenance

Subtotal (Variable Cost)

Insurance

Depreciation

Return on Investment (ROI)

Subtotal (Fixed Cost)

Total Costs

Cost/Mile

$0.00 $1.00 $2.00 $3.00

Tractor with 48 foot trailer

(1,400 tire capacity)

Box truck

(400 tire capacity)

Pickup with trailer

(250 tire capacity)

Pickup truck

(50 tire capacity)

Exhibit 6-1. Capital and Operating Cost Comparison (Cost/Mile) 

(See Appendix F for specific data)

Exhibit 6-2. Hauling Efficiency (Cost/Mile/Tire) 

(See Appendix F for specific data)
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Chapter 6: Transportation and Processing Economics Scrap Tires:

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(1) Pricing quoted on a delivered basis for 

competitive reasons may include significant 

transportation costs. Therefore, transportation 

expenses reduce the net revenue received by 

the recycling facility. For example, at $2.00/mile 

and 40,000 pounds/truckload, one-way trucking 

costs are about $0.01/pound for each 200 miles 

covered and would double if the truck returns 

unloaded. Additionally, transportation costs to 

distant markets from remote facilities can be 

expensive, reducing or eliminating any profit 

from these sales.

(2) Current pricing may be negatively affected 

by competitive efforts to displace current 

suppliers from existing markets. A new supplier 

often has to offer an economic advantage to 

be considered, causing a price shift across all 

markets and cutting into profit margins. 

Government grants and subsidies can be helpful 

in developing applications and processors, but 

government must develop a sound plan to avoid 

negative impact. For instance, government 

grants for processing equipment can be counterproductive by creating unfair competition 

between existing processors who purchased 

their own equipment and new producers who 

receive free equipment through grants. The 

existing producer may fail due to its economic 

disadvantage and the new producer may also 

fail due to lack of operating experience. Market 

subsidies can also be counter-productive by 

creating false economics. Many subsidized 

markets are unable to survive when subsidies are 

eventually discontinued. 

Raw Material Supply – Process and equipment 

requirements depend on the type and quantity 

of waste tires to be processed. Passenger tires are 

considerably easier to process than steel belted truck 

tires. This is especially true with the introduction of 

new, long-life truck tire carcasses that contain higher 

percentages of reinforcing wire. However, passenger 

tires contain more reinforcing fabric that can hinder 

ground rubber production and white lettering 

pigments that result in white specks in ground rubber. 

New “super single” medium truck tires substitute 

one larger tire for two regular truck tires, but these 

tires can be difficult to shred because of their greater 

width. If a specific type of tire casing is required, 

producers should consider whether it is readily 

available now and in the future. In many of the less 

populated areas, tire availability is a controlling factor.

Processing Equipment/System Design – Most 

scrap tire processing systems are conceptually simple 

and represent a balance of required economics, 

productivity, and product quality. Economic 

compromises may be self-defeating if salable 

product is not consistently produced. In developing 

tire processing systems, multiple components are 

normally assembled in series, with the design of 

each component optimized for its specific task. 

However, the impact of series operation on overall 

system reliability is often ignored. When multiple 

components are integrally interlocked in series, 

overall system reliability generally becomes the 

product of each component’s reliability. For 

instance, the overall reliability of a process using 

five interlocked components with individual 90 

percent operating factors will be 0.9 x 0.9 x 0.9 x 

0.9 x 0.9, or 59 percent. When a system is designed 

with this perspective, overall productivity can be 

enhanced by separating sections with interim 

storage to allow partial production when one 

section is not functioning.

Placing equal emphasis on performance of all 

components can also improve productivity, even 

in comparatively simple systems. Attention is 

often focused on major equipment, while simple 

equipment such as conveyors and transfer points 

become afterthoughts. However, improperly 

designed transfer points that clog frequently can 

have a greater impact on system productivity than 

inadequate shredder maintenance.

These are just a few of the major issues that 

should be considered before a process is 

developed or equipment is selected. Many of 

the early processors in the U.S. failed because of 

the absence of markets, bad equipment choices, 

intense price competition, poor quality products, 

and bad operating practices. Subsequent 

successful operations have generally evaluated 

markets, equipment, and economics before they 

make an investment and have learned the value of 

proper maintenance and product quality control. 

Unfortunately, some processors continue to damage 

markets by unreliably supplying poor-quality 

products until both the processor and the markets 

fail. It is generally far less expensive to define critical 

parameters before the system is built than it is to 

modify, or completely rebuild, the system later.

Methods and Equipment

There is a broad selection of commercially available 

tire processing equipment, but it generally falls into 
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Chapter 6: Transportation and Processing Economics Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

one of the three major functional classifications 

discussed below:

Size Reduction

The first step in tire processing is shredding to 

reduce the tire’s size. Most shredders contain 

rotors that consist of a series of alternating cutting 

discs and spacers slipped onto a shaft. Two rotors 

are mounted within a cutting chamber, with the 

cutting disc of one rotor facing a spacer from 

the other rotor. These are called opposing rotors 

because the tops of both rotate toward the center, 

drawing tires between the close-tolerance knives 

and sheering them into strips. Some shredders use 

a single rotating shaft to draw and shear tires through 

stationary knives. Critical variables and operating 

parameters in shredders include:

Knife Type – Shredders generally use either: (1) 

integral discs with a series of extended metal hooks 

on the outside edge called “hook-shear” shredders, 

or (2) discs with attachable metal cutting blocks 

bolted onto the exterior perimeter called “detachable 

knife” shredders. Both operate at low speed and 

high torque to shear the tires between the knives. 

Examples of the hook shear and detachable knife 

shredders are pictured in this section.

Knife Width – Knife width is generally about 5 

cm (2 inches). Knives can be stacked against each 

other to create a 10-cm (4-inch) knife width, thereby 

increasing throughput and shred size for products 

such as Type B TDA. Some primary shredders use 

unique designs with knife spacing as large as 15 cm 

(6 inches), such as the shredder shown in Exhibit 

6-3. In some cases, knife width varies within the 

machine so that larger knives can be re-sharpened 

and inserted into a narrower slot, thereby prolonging 

knife life. Since hook shear knives are removed 

from the shaft for maintenance, different knife and 

spacer configurations can be installed during routine 

maintenance. The rotor assemblies on detachable 

knife shredders are fixed during initial assembly and 

are not changeable without replacing the rotors, but 

different size knives are commonly used in a single 

shredder or in multiple shredders (if more than one is 

used) to maximize knife life.

Knife Tolerance/Maintenance Requirements – The 

tolerance between knives is generally 3 to 5 mils (a 

unit of measure equal to one thousandth of an inch 

or 0.0254 millimeters) initially to shear the reinforcing 

wire in tires. As the knives wear, tolerance increases 

“Hook shear” type shedder

Photo courtesy of Granutech Saturn Systems Corporation, Dallas, TX

”Detachable knife” type shredder

Photo courtesy of Columbus McKinnon Corporation, Sarasota, FL 

Exhibit 6-3. Tire shedder with 6-inch spaced knives 

Photo courtesy of Barclay Roto-Shred Inc., Stockton, CA
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and the reinforcing wire is drawn through the space 

rather than sheared. Progressively longer extensions 

of wire therefore occur outside the rubber chip on 

the resulting product. Extended wire can make the 

product unsalable to some markets. In addition, 

failure to cut cleanly creates lateral stresses that can 

lead to shaft scoring, shaft and bearing failure, and 

other expensive repairs. Failure to maintain knife 

sharpness is a short-term savings that seriously 

increases the cost of long-term machine maintenance. 

Knife Life – Knife life depends on many variables, 

especially product size and contamination. Shredding 

to small tire piece increases wear by requiring more 

recycle (passes through the shredder) and more cuts. 

Contamination with other materials can be abrasive, 

and larger materials can seriously damage shredders. 

Knives generally last three to five times longer on 

detachable knife shredders because of the metallurgy, 

but take two to four times longer to replace when 

replacement is necessary. Either type can be used 

on larger shreds, but detachable knives are generally 

used on nominal 2.5 cm (1-inch) shred such as TDF.

Shaft Considerations – Shafts experience high 

stress as tires are drawn through the opposing rotors. 

Shaft design, size, and heat treatment control the 

shredder’s ability to process both passenger and 

truck tires reliably for extended periods. Undersized 

shafts in smaller, inexpensive machines may deflect 

during operation, decreasing knife life and causing 

fatigue failure. Improper shaft heat treatment during 

manufacture will also lead to premature stress 

failure. Shafts 10 cm (4 inches) or smaller will handle 

only passenger tires and generally indicate minimal 

shredder construction with limited life. A “bargain” 

shredder is generally not a long-term bargain.

Wear Points – Shredders experience wear at all points 

in contact with tires, shreds, or liberated reinforcing 

wire. Good units have readily replaceable wear plates 

or thick hard facing in exposed areas and protect 

shaft bearings from exposure to liberated wire.

Liberation

After the tire has been shredded, higher-speed 

machines are commonly used to liberate reinforcing 

wire and fabric while producing 2.5 cm (1 inch) 

and smaller particle sizes. These machines have 

staggered knives bolted onto one large central rotor. 

An internal view of a Columbus McKinnon (CM) 

Liberator is shown in the photo. Major manufacturers 

of demonstrated high-volume machines include the 

Columbus McKinnon Liberator, Eldon Heavy Rasper, 

and Granutech-Saturn Grizzly. Traditional granulators 

with more than three veins can also be used in lowervolume installations or for subsequent size reduction. 

The rotor knives drag shreds through the space 

between the rotor and hit bars or screens located 

around the casing. Once liberated, steel is captured 

by cross-belt and end pulley magnets, and fluff is 

removed by vibration tables or aspiration.

These units operate with larger tolerance because 

the objective is to tear the wire and rubber, not 

to cut them cleanly. Screens set up around the 

perimeter control product size by allowing small 

particles to escape while larger ones continue to 

be reprocessed. The product has a broad range of 

sizes, requiring subsequent screening to narrow the 

product size range. These machines are extremely 

maintenance intensive, requiring daily maintenance 

in high-volume installations. These units are also 

vulnerable to heat buildup, leading to fires within 

the machines that can be spread to other areas by 

burning product or conveyors. Water injection, fluff 

scrap tire aspiration, and fire control systems are 

Internal view of CM Liberator 

Photo courtesy of Columbus McKinnon Corp. 
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some measures used to control the probability and 

consequences of fires in these machines. 

Classification

Classification is normally used to separate defined 

chip or ground rubber particle sizes. A trommel is a 

screened size separator normally used on large shreds 

such as Type B TDA with the larger pieces returned 

to the shredder for additional size reduction. Disc 

screens and tapered slot screens are used during 

production of smaller pieces, such as 5 cm (2-

inch) and 2.5 cm (1-inch) chips. Vibrating screens 

separate ground rubber by designated mesh size 

to yield specification products. These classification 

technologies are all commonly available and 

recognized.

Processing Economics

Properly constructed scrap tire production 

facilities are capital-intensive. If they are not 

capital-intensive initially, they will be by the 

time the facilities are operating properly or fail. 

This discussion is intended to provide a generic 

overview of processing economics and the impact 

of product size and annual volume on economics. 

To illustrate volume impact, variable and fixed 

costs were examined for processing of 250,000, 

500,000, and 1,000,000 tires/year. Production 

of large Type B TDA (see Tire Derived Aggregate 

Section), nominal 5 cm (2-inch) chips, and nominal 

2.5 cm (1-inch) chips were examined to illustrate 

the impact of piece size. The basis for the capital 

and operating costs for these scenarios are 

provided in Appendix G, along with discussion 

of normal site requirements such as land, paving, 

building, fencing, and other considerations. 

Approximate capital and operating costs are 

provided for each of the product sizes. All costs 

were based on U.S. experience, and then converted 

into equivalent conditions in Mexico. However, 

economics can vary widely and should be adjusted 

to reflect local conditions before any business or 

investment plans are made. 

Processing economics are extremely volume 

sensitive. The impact of differing volumes can be 

illustrated by comparing the capital and operating 

costs for three processing rates of a facility producing 

a Type B TDA. Based on the capacity of durable 

equipment, all three volumes can be produced in 1 

shift/day, 5 days/week. Each facility is unique in its 

productivity, system equipment, layout, labor costs, 

utility rates, and product mix, and each operation will 

have different economics. Therefore, the following 

projections are intended only to provide a basis for 

volume comparison. 

A tire processing facility has the same basic 

components regardless of production capacity. 

Larger plants may have more components in series or 

parallel to increase total capacity. Smaller plants that 

choose to have smaller equipment have historically 

been unsuccessful. Equipment selection is dictated 

by tire construction and strength, so small equipment 

may not be durable even at low volume. 

Approximate variable cost projections for each of 

these processing rates are provided in Appendix 

H. Major cost components include labor, power, 

maintenance, and wire disposal (if necessary). 

Projected labor costs include applicable taxes and 

benefits and can vary widely based on location. It 

should be noted that qualified on-site supervisors 

capable of identifying and implementing proper 

operational and maintenance procedures are a critical 

part of a successful operation, and proper training for 

this role is essential. Scrap tire processing requires 

manual labor and monitoring positions regardless of 

processing volume, so labor is volume sensitive.

Power costs are also subject to wide variation 

depending on a utility’s rate basis, and motors do 

no generally operate at full capacity. Some utilities 

establish charge rates based on maximum demand 

during a limited period. These maximum demand 

rates can lead to similar monthly power costs for 

low- or high-volume facilities if steps are not taken to 

control maximum power demand. Staggered, soft 

starts on large motors can reduce maximum power 

draw significantly. Operating during off-peak hours 

can also reduce power costs.

Maintenance costs depend on specific machinery and 

operating conditions. However, knife life is generally 

shorter than is projected by the manufacturer. In 

addition, deferring necessary knife replacement 

normally results in accelerated deterioration of 

other components, including shafts, bearings, and 

the cutting box. Equipment requires periodic major 

maintenance, but this cost is often not recognized 

during initial operation. It cannot be ignored 

when the machine breaks down and requires 

substantial rebuilding, however. Therefore, projected 

maintenance costs are two to three times higher than 

estimated by the manufacturer to reflect operating 

realities such as contamination and periodic major 

maintenance items. Bead wire is not recovered and 

recycled in these projections, but disposal costs can 

be significant if chips that contain bead wire cannot 

be used.
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As illustrated in Appendix H, total variable cost per tire 

decreases from $0.47/tire to $0.21/tire as a function 

of increasing volume. Volume sensitivity results 

from relatively fixed labor costs for minimal staffing, 

even though some other major costs are directly 

proportional to throughput. 

Operators sometimes focus their attention on variable 

costs and fail to recognize the impact of fixed costs. 

However, fixed costs are economically significant 

and show considerably greater variation in volume 

since administrative and capital charges are not 

directly proportional to volume. Comparative fixed 

costs are also provided in Appendix H, including 

administration, capital, and general components.

Administrative staffing varies with tire collection and 

product marketing requirements. Administrative 

savings can be self-defeating if inadequate time 

or resources is devoted to critical marketing or 

management functions. Professional services such as 

legal, accounting, and technical assistance are often 

ignored, resulting in higher ultimate cost associated 

with inefficient use of management time and 

resources. Equipment depreciation is also a real cost 

in tire processing. Even with proper maintenance, 

equipment simply reaches a point where replacement 

is less expensive than continued repair and 

downtime. Likewise, insurance and property taxes 

can be significant. As a result, fixed costs per tire are 

extremely volume sensitive, falling from $0.84/tire to 

$0.26/tire with increasing volume. Fixed costs show 

even greater variation if interest expenses associated 

with borrowed capital are included. 

Total fixed and variable processing costs can decline 

from $2.31/tire to $0.71/tire with increasing volume 

(including a 25 percent annual return on investment). 

Combined revenue from tipping fees and product 

sales must equal or exceed total processing costs for a 

facility to remain economically viable on a long-term 

basis. As a result of this volume sensitivity, a smallvolume producer would probably be unprofitable. A 

comparatively high-volume regional manufacturer 

should prove to be an economically viable alternative, 

especially in major population centers. 

Similar costs were calculated for facilities making 

5-cm (2-inch) and 2.5-cm (1-inch) chips to illustrate 

the impact of particle size. These costs are provided 

in Appendix H. Total costs for 5-cm (2-inch) chips 

decrease from $3.18/tire to $1.00/ tire at higher 

volumes, which is significantly higher than for Type 

B TDA at comparable volume. The cost range for 

nominal 2.5-cm (1-inch) chips is $3.46/tire to $1.15/

tire, higher than for 5-cm (2-inch) chips. 

This volume and size impact is summarized in the 

table below. With production of Type B TDA at 1 

million tires/year as the baseline, other total costs 

have been ratioed as percentage increased from 

this base. The data clearly indicate that a careful 

evaluation of projected operating volumes and 

products is required before the investment is made.

ECONOMIC SENSITIVITY

A detailed analysis of ground rubber economics is 

not presented because short-term development 

of adequate markets in Mexico is unlikely, 

and ground rubber facilities have even higher 

volume sensitivity because of the higher capital 

and operating costs. However, a schematic 

representation of a ground rubber facility is 

provided in Exhibit 6-4. 

A turn-key ground rubber facility capable of 

producing 5,000 pounds of ground rubber per 

day was recently quoted at more than $4 million 

plus land, building, concrete, electrical supply, 

and related costs. Total costs would exceed $5 

million, or more than $1,000 per pound per day. 

Capital costs of this magnitude are unlikely to 

be sustainable at low volume as markets slowly 

develop. The best opportunity for success would 

involve adding a machine such as a Liberator, 

Rasper or Grizzly (with associated classification 

equipment) to a centralized tire shredding 

facility. This machine could produce product 

sizes ranging from mulch to synthetic turf infill 

in varying quantities. Ratios could be altered by 

changing screens on the granulator to produce finer 

material or by addition of a cracker mill to further 

reduce particle size for finer ground rubber. This 

material could be used to develop markets if similar 

materials cannot be purchased less expensively from 

existing producers in the United States or Europe. 

This equipment generates significant quantities of 

liberated reinforcing wire and fabric that must be 

separated from the rubber. Wire can be reused as a 

steel feedstock in foundries, but may require blending 

PRODUCT VOLUME (tires/year)

250,000 500,000 1,000,000

Type B TDA +225% +70% Baseline

Nominal 

2-inch chip +348% +138% +40%

Nominal 

1-inch chip +387% +166% +62%

Table 6-1. Volume and Size Impacts to Total Cost
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Exhibit 6-4. Schematic representation

Source: Columbus McKinnon Corporation

with other feedstock or additional processing 

to reduce rubber contamination or increase its 

density. The fabric has limited use as a fuel in 

cement kilns. 

SUMMARY

There are many critical components to the 

successful implementation of a scrap tire 

management program. Transportation, tire 

processing, and market potential are three key 

factors to consider before implementation. 

Attention to travel distance, volume and frequency 

of tire collection, loading techniques, and other 

aspects can help lead to optimal equipment 

usage and ultimately achieving an economically 

sound transportation and tire collection program. 

Additional thorough understanding of the markets, 

specifications, pricing, and raw material availability 

for scrap tire processing can prevent letdowns similar 

to those seen by prior U.S. processors. The success or 

failure of new and established programs may also be 

affected by variables such maintenance, personnel, 

and administrative duties. Experiences of attempted 

and established programs in the U.S. can serve as 

valuable lessons learned for potential programs in 

Mexico. 
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Scrap tires are a concern for Mexico, with many 

scrap tire piles concentrated throughout the U.S – 

Mexico border region. In addition to the numerous 

environmental and public health concerns that scrap 

tire piles can raise in communities, they represent a 

vastly underutilized market for recycled materials. 

This scrap tire resource handbook has presented a 

variety of viable options for the Mexico border region 

to take advantage of the scrap tire market. Many 

U.S. states have been able to successfully clean up 

scrap tire stockpiles, establish programs to halt the 

formation of future stockpiles, and mitigate the risks 

posed to human health and the environment posed 

by tire stockpiles. This handbook reflects the lessons 

learned in the process of reaching that success. 

This handbook highlights the important 

considerations for establishing and implementing 

scrap tire abatement and reuse programs. The 

following key points will aid in the successful 

implementation of a scrap tire program: 

•	 Promote and identify markets for scrap tires in or

around your community. 

•	 Identify a specific market before choosing a

particular scrap tire application, such as crumb 

rubber or tire shreds. 

•	 The use of tire-derived fuel is a beneficial use of

scrap tires as long as there are adequate emission 

controls on the facility that will use scrap tires as 

fuel. 

•	 The use of scrap tires in civil engineering

applications, in some cases, can be a viable 

alternative to tire-derived fuel, as highlighted in 

Chapter 5.

•	 The economic analysis as described in Chapter

6 is critical to scrap tire program success; 

transportation, tire processing, and market 

potential are three key economic factors to 

consider before implementation.

•	 It is important to involve an experienced scrap

tire expert before making a decision to spend 

money on pyrolysis, gasification, or thermal 

induction. While these methods are evolving 

and may become economically viable in the 

future, they have not proven economically 

viable thus far. 

Additional information, lessons learned, and 

case-studies from established programs can be 

found throughout the handbook; links for further 

reading are supplied when available and will 

provide valuable information to local government 

or private industry ready to explore the scrap tire 

market. 

CHAPTER 7

Conclusion

Scrap tire pile near Ciudad Juarez

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GLOSSARY

Abatement: The removal of scrap tires from stock 

piles or other sites with accumulations of whole or 

shredded scrap tires. 

Abrasion: Wearing away by scraping or rubbing. The 

progressive wearing away of a tire tread in service. 

Accelerant: A substance used to speed up the 

combustion process. 

Accelerator: A substance added in small amounts to 

uncured rubber compounds prior to the vulcanization 

process to reduce the time required for vulcanization. 

Aggregate: Rock or stone of uniform size or a range 

of sizes from either naturally occurring deposits or 

from artificially prepared materials. Other materials 

such as scrap tire shreds can be used in some cases to 

replace rock or stone. 

Course Aggregate: Aggregate predominately 

retained on number 4 sieve.

Fine Aggregate: Aggregate passing the 3/8th 

inch sieve and almost entirely passing the number 

4 sieve.

Aging: Deterioration of physical and chemical 

properties by oxidation over a period of time. 

Air Pressure: Force exerted by air within the tire; 

expressed in pounds per square inch, kilopascals or 

bars. 

Air Void: A space in cement paste, mortar, or concrete 

filled with air. 

Alignment: Adjustment of steering and suspension 

components to facilitate the most efficient operation 

of all tire and wheel assemblies as related to vehicle 

control and tire wear. 

All Season Radial: A highway tire designed to meet 

the weather conditions in all seasons of the year 

and which meet the U.S. Rubber Manufacturers 

Association definition of a mud and snow tire. 

Altered Tire: A scrap tire which has been modified so 

that it is no longer capable of holding or retaining air, 

water or being used on a vehicle. 

Alternative Means of Protection: An application 

to use another form of fire protection over what is 

required by code or regulation. 

Ambient Rubber: Rubber processed without 

freezing.

Ambient Temperature: Temperature of the media 

surrounding an object; such as the air temperature 

in which a tire may be running or is being processed 

(shredding); typically this is the same temperature of 

the room or the outside area being used to process 

the tire. 

Anaerobic: The ability for microorganisms to live 

without the presence of oxygen. 

Annual Take-Off: The number of scrap tires 

generated in any calendar year. 

Antioxidant: A chemical used to retard 

deterioration specifically caused by oxygen. 

Antiozonant: A chemical compounding material 

used specifically to retard deterioration caused by 

the ozone. 

Arm-Dump Railcar: A type of railcar used to 

transport materials.

Arson: The criminal act of burning property. 

Asphalt: A dark brown to black cement-like 

material in which the predominant constituents 

are bitumens which occur in nature or are 

obtained from petroleum processing. 

Asphalt Binder: The asphalt-cement portion of an 

asphaltic concrete mixture. 

Asphalt Cement: A fluxed or unfluxed asphalt 

specially prepared as to quality and consistency 

for direct use in the manufacture of bituminous 

pavements. 

Asphalt Concrete: An aggregate mixture with an 

asphalt cement binder. 

Asphalt Rubber: A blend of asphalt cement, ground 

tire rubber, and certain additives in which the rubber 

component is at least 15 percent by weight of the 

total blend and has reacted in the hot mix asphalt 

cement sufficiently to cause swelling of the rubber 

particles. 

Asphalt Rubber Chip Seal: A thin layer of crumb 

rubber-modified asphalt used to bind an aggregate 

wearing course to a roadway surface. 
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Glossary Scrap Tires: Handbook on Recycling Applications and

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Aspiration: The uptake by suction of tire fluff or other 

light materials into tire processing machinery.

ASTM D11 Rubber Committee: A committee 

formed by the American Society for Testing and 

Materials (ASTM). The scope of the committee is 

the formulation of the test methods, definitions, 

specifications, practices, and classifications pertaining 

to rubber, rubber products, and systems and services 

appropriate to rubber technology. 

Backing: The material used on the application side 

of tread rubber, repair units, and tube patches to 

ensure cleanliness, tackiness and ease in shipping 

and storing. 

Bagel Cut: Cutting the tire in half along its 

circumference. 

Baghouse: Designed to handle heavy dust loads, 

a dust collector system consists of a blower, dust 

filter, a filter-cleaning system, and a dust receptacle 

or dust removal system. It is distinguished from air 

cleaners which use disposable filters to remove 

dust.

Baling: A method of volume reduction whereby 

tires are compressed into bales. 

Balance: The distribution of weight around a tire 

or tire/wheel assembly. The uniform distribution 

of weight will produce a balanced tire. 

Base Course: A sub-layer material of an asphalt 

road to provide a foundation to support the top 

layer(s) of the pavement. Generally consists of a 

specific type of construction aggregate that is a 

middle surface below the sub-grade and above 

the sub-base underneath an asphalt road or that is 

placed directly on top of the undisturbed soil. 

Batch Plant: A manufacturing facility for producing 

bituminous paving mixtures that proportions the 

aggregate constituents into the mix by weighted 

batches and adds bituminous material by either 

weight or volume. 

Barrel Stack: A means of storing tires, where the 

tires are neatly stacked one upon another. 

Bead: The anchoring part of the tire which is shaped 

to fit the rim. The bead is constructed of high tensile 

steel wires wrapped by the plies. 

Bead Separation: Loss of adhesion between the 

components in the bead area of a tire. 

Bead-to-Bead Measurement: A measurement from 

the bead across the crown to the opposite bead, 

taken after buffing to ensure selection of the correct 

matrix size in which to cure a retread. 

Bead-to-Bead Retreading: A retreading process 

which includes veneering of the sidewall from the 

shoulder to the bead. 

Bead Wire: A high tensile steel wire, surrounded by 

rubber, which forms the bead of a tire that provides a 

firm contact to the rim. 

Bear Claw: The rough-edged bead wire sticking out 

from a shredded tire. 

Belt: An assembly of rubber coated fabric or wire 

used to reinforce a tire’s tread area. In radial tires, it 

also constrains the outside diameter against inflation 

pressure and centrifugal force. 

Belt Wire: A brass plated high tensile steel wire cord 

used in steel belts. 

Bias Ply Tires: A tire built with two or more casing 

plies which cross each other in the crown at an angle 

of 30 to 45 degrees to the tread centerline. 

Binder: A component material which when mixed 

with water or other liquid hardens to hold together 

aggregate particles into a rigid heterogeneous mass. 

Bitumen: A class of black or dark-colored cementlike substances, natural or manufactured, composed 

principally of high molecular weight hydrocarbons, of 

which asphalt, tars, pitches and asphaltites are typical. 

Bituminous: Materials containing or treated with 

bitumen. 

Bleeding: The autogenous flow of mixing water 

within, or its emergence from newly placed concrete 

or mortar caused by the settlement of the solid 

materials within the mass. 

Bleeding A Tire: The practice, not recommended by 

the tire manufacturers, of letting hot air out of tires 

under load and after they have been running in order 

to reduce inflation. 

Blowout: Instantaneous rupturing of tire body, 

causing complete loss of air pressure. 

Blue Triangle: A bulge due to a section repair is 

allowed not to exceed 3/8th of an inch (1 cm) in 

height. This bulge may sometimes be identified by a 

blue triangle label in the immediate area. 
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Body: Tire structure not including the tread (also refer 

to casing and carcass). 

Bond: A type of insurance agreement which provides 

a financial guarantee or pledge that an undertaking 

will be completed. Or a guarantee from financial loss 

caused by the act, or default, of a third person. Fixed 

sums are paid annually until bond maturity then 

repayment of principle is expected.

Borehole: A deep, narrow hole bored or drilled in the 

earth to extract a liquid, for building construction or 

to collect samples for analysis.

Brand Number: A number branded into one or both 

sidewalls of a tire by the customer for identification 

purposes. 

Break: A rupture or opening in the tire structure. 

BTU: British Thermal Unit; defined as the amount 

of energy required to heat one pound of water one 

degree Fahrenheit. 

Buckle: The wrinkling or abnormal deflection of the 

sidewall when the tire is under- inflated, over-loaded 

or under severe strain; the abnormal deflection in the 

belts as a result of improper retreading. 

Buffer: The equipment used to remove the old tread 

from the tire that is to be retreaded. A powerful rotary 

rasp that provides a rough, clean, even surface to 

which new rubber readily adheres. A flexible shaft 

buffer is used for preparing a small area for repairing. 

Buffing: The process of removing worn/used tread 

from a tire to be retreaded. A rotating rasp that 

provides a rough, clean, even surface to which new 

rubber readily adheres. A flexible shaft buffer used 

for preparing a small area for repairing. Buffings can 

also be produced during the manufacturing of a tire 

by grinding to expose white rubber on a finished tire, 

creating a white sidewall or raised white letters on the 

tire. 

Buffing Dust: See Buffings. 

Buffing Rubber: A term used by ASTM D11 Rubber 

Committee. Particulate rubber produced as a 

byproduct of the buffing operation in the carcass 

preparation stage of tire retreading. It is characterized 

by a wide range of particulate sizes which are 

predominately elongated or acicular in shape. (also 

refer to Particulate Rubber). The appearance of the 

unique shape of the particles of this material is only 

apparent in finished goods or products which contain 

particles having a dimension greater in size than (30 

mesh). 

Buffings: Vulcanized rubber usually obtained from 

a worn/used tire in the process of removing the old 

tread in preparation for retreading. This material 

is typically used in molded rubber products. Also 

referred to as buffing dust.

Build-Up: The application of retread or repair rubber. 

Bulge: A protrusion or raised area, usually in the tire 

sidewall. 

Burn-It: A fire fighting strategy that would allow for 

the free-burn of a tire pile fire. 

Bury-It: A fire fighting strategy that suggests 

burying a tire pile with soil, sand, gravel, cement 

dust or other cover material. 

Butyl Rubber: A general purpose synthetic 

elastomer (rubber) produced by copolymerizing 

isobutylene with a small amount of isoprene. 

Butyl rubber has a low permeability to gases. Its 

impermeability to air is 70 percent better than 

natural rubber; for this reason is superior for liner 

tubes and for tubeless tire inner liners. 

Calcining: Heating a substance to a high 

temperature, but below its melting point, to bring 

about thermal decomposition.

Carbon Black: A material used in tires that 

provides strength to rubber compounds. This 

material consists essentially of elemental carbon 

in the form of near spherical colloidal particles 

and aggregates. Carbon black is obtained by 

partial combustion or thermal decomposition of 

hydrocarbons. 

Carcass: The basic tire structure excluding the 

tread (also referred to as a Casing). 

Casing: The main body of the tire but not including 

the tread or sidewall rubber. 

Casing Jockey: An individual or an independent 

business that collects used or scrap tires from tire 

vendors or automotive disassembly facilities and 

transports them to another location. (also refer to 

Tire Jockey). 

Catalyst: A chemical that in small quantities speeds 

up the reaction of a resinous material but is not itself a 

necessary part of the final product. 

Celsius: A temperature scale in which zero (0) degrees 

is the freezing point and 100 degrees is the boiling 

point (formerly called centigrade). 
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Glossary Scrap Tires: Handbook on Recycling Applications and

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Change-Over: The removal of tires on cars or trucks 

and substitution of a different size or type of tire. 

Char: The solid residue remaining after pyrolysis of a 

tire and after removal of steel, fiber or other support 

material. 

Checking: Minute cracking in the surface of rubber 

caused by aging and oxidation. 

Chemical Cure: Vulcanization at room temperature 

or above activated by chemical agents without the 

application of heat from an outside source. 

Chip-Chunk: Refer to Chunking. 

Chip Seal: A thin layer of sprayed asphalt, with 

or without rubber, and subsequent aggregate 

placement used to prolong pavement surface life. 

Chipped Tire: Pieces of scrap tires that have a basic 

geometrical shape and generally smaller than 6 

inches by 8 inches in size (also refer to Tire Chip). 

Chipping: Refer to Chunking. 

Chopped Tire: A scrap tire that is cut into 

relatively large pieces of unspecified dimensions. 

Chunking: The loss of either small or substantial 

pieces of the tread caused by the cutting or 

breaking action of rough terrain or poor highway 

surfaces. This is normally associated with highway 

tires when incorrectly used off the road. Also 

referred to as chipping or chip-chunk. 

Civil Engineering Application: The use of scrap 

tires in lieu of natural occurring materials (i.e., rock, 

sand, dirt, gravel) in construction. 

Clam Shell: Refer to Bagel Cut. 

Classifier: Equipment designed to separate 

oversized tire shreds from the desired size. 

Combustion: The chemical reaction of a material 

through rapid oxidation with the evolution of heat 

and light. 

Commercial Tires: Truck and industrial tires. 

Compacted Tire: Refer to Baling. 

Compound: A mixture of blending chemicals 

specifically tailored to the needs of the specific 

components of the tire. 

Compressible inclusion: Used in applications where 

a strong yet lightweight material is required to reduce 

stresses on structural elements.

Concrete: A composite material that consists 

essentially of a binding medium within which are 

embedded particles or fragments of aggregate; in 

hydraulic cement concrete, the binder is formed from 

a mixture of hydraulic cement and water. 

Conflagration: A large, uncontrollable fire.

Containment: A fire fighting operation that prevents 

the further spread of a fire. 

Continuous Mix Plant: A manufacturing facility 

for producing bituminous paving mixtures that 

proportions the aggregate and bituminous 

constituents into the mix by a continuous volumetric 

proportioning system without definite batch intervals. 

Control: The overall fire fighting operation of 

confinement and suppression. A fire is under control 

when the advance of the fire has been halted. 

Converted Tire: A scrap tire which has been 

processed into a usable commodity other than a tire. 

Copolymer: A polymer formed from two or more 

types of monomers. 

Cords: The strands of wire or fabric that form the plies 

and belts in a tire. 

Crambient Rubber: A mixture of ambient and 

cryogenic rubbers. The ambient being less dense than 

the cryogenic, the ambient tends to works its way to 

the top, resulting in inconsistent shock absorption.

Cracker Mill: A machine designed to size reduce 

scrap tires by passing the scrap material through 

rotating corrugated steel drums with angular grooves. 

Cracking: A sharp break or fissure in the surface of 

rubber particles that develops upon exposure to light, 

heat, ozone or repeated bending or stretching. 

Crazing: A surface effect on rubber or plastic articles 

characterized by many minute cracks. 

Cross Linking: When chemical bonds set up between 

molecular chains, the material is said to be cross 

linked. Once cross linked, a material cannot be 

reprocessed. 

CRREL: Cold Regions Research and Engineering 

Laboratory. A U.S. Army Corps of Engineers testing 

laboratory. CRREL has been working on a Chunk 

Rubber Asphalt Concrete mix, which is designed to 

enhance ice-disbonding characteristics of several 

asphalt paving materials. 

Crude Rubber: Natural, unprocessed rubber. 
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Crumb Rubber: (1) A coagulated and dried natural 

latex rubber. (2) Fine particles of vulcanized rubber 

resulting from mechanical or cryogenic size reduction 

of scrap tires or other rubber products. 

Crumb Rubber Modified Asphalt Concrete 

(CRMAC): A general term used to identify a group of 

processes which incorporate crumb rubber modifiers 

into asphalt paving materials. 

Crumb Rubber Modified Asphalt Hot Mix Asphalt: 

Refer to Crumb Rubber Modified Asphalt Concrete. 

Crumb Rubber Modifier: A general term used by 

the U.S. Federal Highway Administration to identify a 

group of processes and concepts which incorporate 

scrap tire rubber into asphalt paving materials. 

Crushed Gravel: The product resulting from the 

artificial crushing of gravel with substantially all 

fragments having at least one face resulting from 

fracture. 

Crushed Stone: The product resulting from the 

artificial crushing of rocks, boulders, or large 

cobblestones, substantially all faces of which have 

resulted from the crushing operation. 

Cryogenics: A crumb rubber modifier production 

process in which scrap tire rubber is frozen using 

liquid nitrogen or commercial refrigeration methods 

to embrittle the rubber. In the cryogenic process, the 

embrittled rubber is crushed in a hammermill to the 

desired particle size. 

Cure: To vulcanize; also time, temperature and 

pressure conditions used to vulcanize rubber. 

Cured-On Tires: Solid industrial tires vulcanized 

directly to the steel wheel on which they run. Also 

called Molded-On Tires. 

Curing: Process of heating or otherwise treating 

a rubber or plastic compound to convert it from a 

thermoplastic or fluid material into the solid, relatively 

heat resistant state desired in commercial products. 

When heating is employed, the process is also called 

vulcanization. 

Debeading: Process of removing the heavy bead 

reinforcing wire around the rim of the tire. Removal of 

the bead wire prior to shredding allows for a cleaner 

end product and provides less wear on the moving 

parts of the shredder. 

Deflection: The distortion of the tire from its normal 

shape. 

Dense Graded Aggregate: An aggregate that 

has a particle size distribution such that when it 

is compacted, the resulting voids between the 

aggregate particles, expressed as a percentage of the 

total space occupied by the material, are relatively 

small. 

Density: A term that denotes the weight per unit of 

volume of a substance. The density of any substance 

can be obtained by dividing the weight of the 

substance by its volume. 

Depolymerization: The process of reducing the 

chain length of polymers by breaking their chemical 

bonds. 

Devulcanization: A process in which there is 

substantial regeneration of the rubber compound 

to its original plastic state, thus permitting 

the product to be processed, compounded or 

vulcanized. Combined sulfur is not affected. 

True devulcanization of vulcanized rubber with 

regeneration of the original rubber and removal of 

combined sulfur has not been accomplished. The 

term is synonymous with reclaiming of vulcanized 

scrap rubber. It is primarily a depolymerization 

accompanied by some oxidation. 

Dewired: The absence of exposed wire on the 

perimeter of the tire chips. Belt wire typically 

remains in the chip, but is embedded in the chip. 

Disposal Fee: Refer to Tipping Fee. 

Dog Tracking: A condition where the rear wheels 

of a vehicle do not follow the path of the front 

wheels. 

DOT Number: An identification number molded 

by the manufacturer into the sidewall of a highway 

use tire in compliance with federal motor vehicle 

safety standard requirements set by the U.S. 

Department of Transportation (USDOT). 

Drown-It: A fire fighting strategy that suggests 

using copious amounts of water on a tire pile fire. 

Dry Process: A paving product made with ground 

rubber as an aggregate component. The rubber is 

mixed with the aggregate prior to blending in the 

asphalt cement in quantities ranging up to three 

percent rubber. This process is also referred to as 

Rubber Modified Asphalt Concrete (RUMAC). 

Duals: The term used to describe a set of two tires 

and wheels used on each end of an axle. 
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Due Diligence: Generally, the degree of care, based 

on information gathering and analysis, which a 

reasonable person would take to evaluate risks before 

entering into an agreement or business transaction 

with another party.

Elasticity: The property of material by how much 

it tends to return to its original size and shape after 

removal of the stress which caused its deformation. 

Elastomer: A polymeric material which, at room 

temperature, is capable of recovering substantially 

in shape and size after removal of a deforming force. 

This term generally refers to synthetic polymers as 

opposed to rubber, which generally refers to the 

natural material. 

Electrostatic Precipitation: The process of 

removing small particles of smoke, dust, oil, 

etc., from air by passing the air first through an 

electrically charged screen that gives a charge to 

the particles, then between two charged plates 

where the particles are attracted to one surface.

Elongation: A characteristic of rubber which 

measures the point to which it can be stretched 

without breaking.

Embrittlement: A rubber compound becoming 

brittle during low or high temperature exposure 

or as a result of aging. 

End User: (1) The last entity who uses the tire, in 

whatever form, to make a product or provide a 

service with economic value for other uses. (2) The 

facility which utilizes the heat content or other 

forms of energy from the combustion of scrap tires 

for energy recovery. 

Energy Recovery: A process by which all or part of 

the tire is utilized as fuel to recover its BTU value. 

See Tire Derived Fuel (TDF). 

Exothermic: A chemical reaction in which heat 

energy is liberated. 

Extender: (1) An inert material added to a 

compound to increase volume and lower cost (2) An 

organic material used to augment or replace part of 

the polymer in a compound. 

Extruder: A machine with a driven screw for 

continuous forming of rubber by forcing it through a 

die. 

Extrusion: Process of mixing, heating, and forcing a 

raw material through a die to produce a continuous 

shape.

Fabric: Textile cords used in tire manufacturing. 

Face -of a tire: A term commonly used to denote the 

surface area of the tread of an off- the-road tire. 

Fatigue Cracking: Cracks in a road surface resulting 

from repeated compression by vehicle weight. 

Feedstock: A raw material supplied to a machine or 

processing plant for the industrial manufacture of a 

product.

FHWA: Federal Highway Administration, a part of the 

U.S. Department of Transportation. 

Filler: A solid compounding material which may be 

added, usually in finely divided form, in relatively 

large proportions, to a polymer. 

Financial Assurance: A performance bond, letter 

of credit, cash deposit or other mutually acceptable 

financial instrument used to guarantee performance. 

Fines: (1)Small particles of graded aggregate used 

in asphalt concrete composition. (2) Small particles 

of ground rubber that results as a by-product of 

processing scrap tires into granules. 

Fishhooks: Strands of belt or bead wire exposed from 

a processed scrap tire or an individual piece of belt or 

bead wire (also refer to Bear Claw). 

Flash: Excess rubber squeezed between the edges of 

mold segments during the curing process. 

Flash Point: The lowest temperature at which the 

vapor of a combustible liquid can be made to ignite 

momentarily in air.

Fleet Service: The professional rendering of tire 

maintenance service to the truck operator or other 

user. Usually includes the periodic inspection of all 

rolling wheels at the fleet’s place of business. 

Fluff: The fibrous, non-rubber, non-metal portion of 

a tire which remains after the scrap tire is processed 

(i.e., cotton, rayon, polyester, fiberglass or nylon). 

Footprint: The impact made by a tire’s tread that 

comes in contact with the ground. 

Full Cap: A retread process that includes replacing 

the shoulder area and the tread area of the tire. 

Full Retreading: The process of buffing scrap tires 

in the following way: across the top of the tread, 

down over the shoulder to the upper sidewalls, and 

replacing the tread and/or sidewall rubber. This 
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retread method will give the shoulders a finished 

appearance similar to that of a new tire. 

Gasification: A process that occurs when tires 

are subjected to a high temperature, low oxygen 

environment. 

Generic Dry Process: A non-patented procedure for 

incorporating ground rubber into conventional dense 

or gap graded hot mix asphalt using the dry process. 

Geocomposite: The basic philosophy behind 

geocomposite materials is to combine the best 

features of different materials in such a way that 

specific applications are addressed in the optimal 

manner and at minimum cost. Thus, the benefit/cost 

ratio is maximized. Such geocomposites will generally 

be geosynthetic materials, but not always.

Geomembrane: A kind of impermeable geosynthetic 

material used widely as cut-offs and liners. The 

physical material properties of geomembranes 

include thickness, density, water vapor transmission, 

solvent vapor transmission, and melt flow index.

Geosynthetic: A range of generally polymeric 

products used to solve civil engineering problems. 

The term is generally regarded to encompass eight 

main product categories: geotextiles, geogrids, 

geonets, geomembranes, geosynthetic clay liners, 

geofoam, geocells (cellular confinement) and 

geocomposites.

Geotextile: Permeable fabrics which, when used 

in association with soil, have the ability to separate, 

filter, reinforce, protect, or drain. Typically made from 

polypropylene or polyester.

Granulated Rubber: Particulate rubber composed 

of mainly non-spherical particles that span a broad 

range of maximum particle dimension, from below 

425um (40 mesh) to 12mm (0.47 in). The key feature 

of this type of particulate rubber is the fraction of 

the material in the greater than 2mm (0.08 in) up to 

12mm (0.47 in) maximum particle dimension range. A 

term defined by ASTM D11, Rubber Committee. See 

Particulate Rubber. 

Granulator: A machine that shears apart scrap tire 

rubber with revolving plates producing ground 

particles, generally 3/4 inch to 200 mesh (also refer to 

Granulated Rubber). 

Gravel: Course aggregate resulting from the natural 

disintegration and abrasion of rock or processing of 

weakly bound conglomerate. 

Green Tire: A tire which has not been vulcanized or 

cured. 

Grooves: The channels between the tread ribs of a 

tire. 

Ground Rubber: Particulate rubber composed of 

mainly non-spherical particles that span a range 

of maximum particulate dimension, from well 

below 425um (40 mesh) to 2.032 mm (0.08 in) as 

a maximum particle dimension. See Particulate 

Rubber. The smallest reported mesh size for ground 

rubber is 450 mesh. The term used by ASTM D11 

Rubber Committee.

Hair: Wire protruding from the perimeter of a tire 

chip or shred (also refer to Fish Hook). 

Hammermill: A machine that mechanically 

processes cryogenically frozen scrap tire rubber 

using rotating impact hammers. 

Hauler: A transporter of goods. A person or 

company whose business it is to transport goods 

or materials, especially by road.

Heat Build Up: The generation of heat due to 

hysteresis when rubber is rapidly or continually 

deformed. 

Heavy-Duty Tires: Tires weighing more than 40 

pounds, used on trucks, buses and off-the- road 

vehicles in heavy duty applications. 

Horizontal Stress: Normal stress on a vertical 

plane.

Horsetail: A rough piece of shredded tire with a 

width of two to four inches, and a length greater 

than six inches. 

Hot Mix Asphalt: A composition consisting 

primarily of graded aggregate and asphalt cement 

widely used for paving.. 

Hydrocarbon: An organic chemical compound 

containing only the elements carbon and hydrogen. 

Hydroplaning (Aquaplaning) of Pneumatic Tires: 

A phenomenon that occurs when the road contact 

surface of a pneumatic tire is separated from the road 

by a fluid, usually water. 

Hysteresis: The heat generated by rapid deformation 

of a vulcanized rubber part. It is the difference 

between the energy of the deforming stress and the 

energy of the recovery material. 
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Incipient: The beginning or early phase of a fire 

where the heat being generated has not extended to 

the surrounding materials. 

Inflation: The amount of air pressure in a tire. 

India Rubber: An early name for natural rubber, as it 

came from the “lndes”. 

Injection Molding: A molding operation wherein 

a rubber compound is heated in the barrel of an 

extruder and injected into the mold cavity while in a 

fluid state. 

Injury: Any damage caused by a penetrating object, 

severe scuff or impact. 

Innerliner: The layer or layers of rubber laminated 

to the inside of a tubeless tire to contain the 

inflation medium. 

Jockey: Refer to Casing Jockey or Tire Jockey. 

Kilojoules: A metric measurement of the release 

of energy. One kilojoule/kilogram is equal to 2.33 

BTU pound. 

Kilopascals (Kpa): Metric unit of measurement for 

air pressure. 

Ko: The coefficient of the pressure that soil exerts 

in the horizontal plane. This pressure is known as 

lateral earth pressure. The common applications 

of Ko are for the design of ground engineering 

structures to determine the friction on the sides 

of, for example, retaining walls and tunnels. 

Laced Tires: See Lacing.

Lacing: A method of stacking tires which 

conserves space. 

Latex: Milk-like liquid that comes from a rubber 

tree. Crude rubber is coagulated from latex. 

Leachate: A liquid containing soluble material 

formed when rainwater or another liquid passes 

downward through soil or other material. Especially 

a solution containing contaminants picked up 

through the leaching. 

Light-Duty Tires: Tires weighing less than 40 pounds, 

used on passenger cars and light trucks. 

Light Truck Tire: Tires with a rim diameter of 16 to 

19.5 inches that are manufactured specifically for light 

truck use. 

Logger Tire: A special tire designed for the logging 

industry. 

Maintenance Mix: A mixture of bituminous 

material and mineral aggregate applied at ambient 

temperature for use in patching holes, depressions, 

and distressed areas in existing pavement. 

Managed Site: A tire pile or storage facility where 

the owner/operator stores or processes scrap tires in 

compliance with the appropriate regulations. 

Matrix: The retreading equipment in which the new 

tread is cured to the worn casing and where the tread 

design is formed. 

Mesh: A size unit describing the number of openings 

per inch in a screen. For example, a 50 mesh screen 

has 50 openings per lineal inch. 

Micro Milling: A mechanical process that further 

reduces ground rubber to very fine particles. The 

process combines ground rubber and water, forming 

a slurry which is forced between rotating abrasive 

discs. 

Micron: A unit of length equal to 0.0001 centimeters 

or 10,000 angstrom units. This term has generally 

been replaced by the term micrometer. 

Millimeter: A metric unit of measurement. 1 

millimeter (mm) equals 0.039 inches. 25.4 mm equals 

1 inch. 

Mixing Tires: Use of different constructions (radial, 

bias, bias-belted) on a vehicle. 

Mold: The heated cavity in which tires are vulcanized. 

Includes the steam chamber, matrices and adjusting 

devices. 

Mold Cure: A retreading process using uncured tread 

compounds where the vulcanization takes place in 

molds. 

Monomer: Any molecule that can be united (bound) 

chemically as part of a unit of a polymer. 

Mucker Tire: A flotation type of tire specifically 

designed for use in soft grounds (also referred to as a 

Mudder). 

Natural Rubber: The material processed from the sap 

(latex) of Hevca Brasiliensis (rubber trees). 

New Tire: A tire which has never been mounted on a 

rim. 

Nominal: A term commonly used to refer to the 

average size product (chip) that comprises 50 percent 

or more of the throughput in a scrap tire processing 

operation. It should be noted that any scrap tire 
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processing operation will also generate products 

(chips) above and below the “nominal” range of the 

machine. 

Off Road Tire: See OTR

Open Graded Aggregate: An aggregate that has a 

particle size distribution such that when compacted, 

the voids between the aggregate particles, expressed 

as a percentage of the total space occupied by the 

material, remain relatively large. 

Original Equipment Tire: The tires supplied with new 

vehicles from vehicle manufacturers. 

OTR: Off the Road Tire; tire designed primarily for use 

on unpaved roads or where no roads exist. Built for 

ruggedness and traction rather than for speed. 

Overinflation: The inflation of a tire above the 

recommended pressure for the load it carries; 

negative byproducts are rough ride, bruise and 

impact damage and suspension system damage. 

Overloading: The practice of putting more weight 

on a tire than the tire is designed for or can carry due 

to low inflation pressure. This is a dangerous practice 

and is not recommended. 

Oversizing: Mounting larger tires than specified on 

a vehicle to carry heavier loads, to provide increased 

flotation or to provide other performance changes. 

Oxidation: The reaction of oxygen with a rubber 

product, usually accompanied by a change in feel, 

appearance of surface or a change, usually adverse, in 

physical properties. 

Ozone: An allotropic form of oxygen. A gas with 

characteristic odor which is a powerful oxidizing 

agent. It is present in the atmosphere at low levels 

and causes cracking in certain types of elastomeric 

compounds. 

Particulate Rubber: Raw, uncured, compounded 

or vulcanized rubber that has been transformed by 

means of a mechanical size reduction process into a 

collection of particles, with or without a coating of a 

partitioning agent to prevent agglomeration during 

production, transportation, or storage (Also refer to 

Buffing Rubber, Granulated Rubber, Ground Rubber, 

and Powered Rubber). The term used by ASTM D11 

Rubber Committee.

Passenger Car Tire: A tire with less than an 18-inch 

rim diameter for use on cars only. 

Passenger Tire Equivalent (PTE): The weight of 

waste tires or parts of waste tires equivalent to the 

average weight of one waste passenger tire. The 

average weight of one waste passenger tire is equal 

to 20 pounds. For example, one 80 pound truck tire 

would be 4 PTEs.

Pavement Distress: The physical manifestation of 

defects or deterioration in a pavement. 

Pavement Performance: The ability of a pavement 

to fulfill its purpose as reflected in the measurable 

change in conditions over time. 

Plantation Rubber: Crude natural rubber obtained 

from cultivated rubber trees as opposed to wild or 

uncultivated trees. 

Plies: Layers of rubber coated cords. 

Pneumatic Tire: A tire which depends on the 

compressed air it holds to carry the load. It differs 

from a solid tire in that the tire itself carries the 

load. 

Polybutadiene: A synthetic rubber made 

by combining many molecules of butadiene 

into long chain polymers. This rubber is noted 

for superior tread wear, resiliency and flexing 

qualities at low temperatures. 

Polymer: A macromolecular material formed 

by the chemical combination of monomers 

having either the same or different chemical 

compositions. 

Polymer Chain: The chain of elements that form 

the basis of the structure of a polymer. 

Polymerization: A chemical reaction in which 

the molecules of a monomer are linked together 

to form large molecules whose molecular mass is 

a multiple of the original substance. When two or 

more different monomers are involved, the process 

is called copolymerization. 

Pounds Per Square Inch (PSI): A measure of 

pressure. 

Powdered Rubber: Particulate rubber composed of 

mainly non-spherical particles that have a maximum 

particle dimension equal to or below 425um (40 

mesh). (Also refer to Particulate Rubber). The term 

used by ASTM D11 Rubber Committee.

Pre-cure Process: A process of using premanufactured treads and vulcanizing these treads to 
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a prepared casing with a thin layer of cushion gum 

(natural rubber). 

Pre-cured Tread: Tread which is vulcanized with 

the tread configuration molded into it prior to being 

placed on the buffed casing. 

Pre-drying: Drying of a tire in a heated room to 

remove moisture before retreading. 

Pre-Incident Planning: A method of anticipating the 

response to a particular fire incident and planning 

the tactics and strategies based on information 

collected before a fire occurs. 

Pressure Build-Up: The increase of air pressure in a 

tire caused by an increase in the temperature of the 

contained air. 

Preventive Maintenance: Maintenance performed 

prior to any failure. Designed to lengthen product 

life, prevent high maintenance costs and to reduce 

equipment breakdown. 

Private Brand: A specialty line of tires or tubes 

manufactured for and to the specifications of a 

private buyer who sells these products under its 

company name. 

Processed Tire: A scrap tire which has been 

altered, converted or size reduced. Methods of 

processing include; cutting, cryogenic reduction, 

or shredding. 

PTE: See Passenger Tire Equivalent. 

Pugmill: A device for mixing the separate hot 

aggregate and bituminous components into 

a homogenous bituminous concrete ready for 

discharge into a delivery system. 

Pulverized Rubber: Refer to Ground Rubber. 

Pull: The tendency of a vehicle to veer to one side. 

Pyrolysis: The process of thermal decomposition in 

the absence of oxygen. Pyrolyzing scrap tires yields 

gas, char, oil and steel. 

Radial Cracking: Cracking, perpendicular to the 

bead, usually in or near the sidewall area. 

Radial Tire: A tire constructed so that the ply cords 

extend from bead to bead at a 90 degree angle to the 

centerline of the tread. 

Rate of Cure: The relative time required to reach a 

predetermined state of vulcanization under specific 

conditions. 

Raw Rubber: Unprocessed, vulcanized elastomer, 

normally implying the natural product. 

Recapping: An improper term for retreading. Often, 

this term refers to the process of top capping, in 

which rubber is applied to the tread surface only. 

Reclaim: The product from the degradation of rubber 

by mechanical, thermal, and/or chemical processes, 

resulting in a depolymerized material. 

Reclaimed Asphalt Pavement (RAP): Asphalt 

pavement or paving mixture removed from its 

original location for use in recycled asphalt pavement 

mixtures. 

Recovery: The degree to which a rubber product 

returns to its normal dimensions after being distorted. 

Recycle or Recycling: Any process by which worn 

tires are transformed into new products including 

retreads, fuel, or ground rubber. 

Recycled Asphalt Paving Mixture: A mixture of 

reclaimed asphalt pavement (RAP) with the inclusion, 

if required, of asphalt cement, emulsified asphalt, cut 

back asphalt, recycling agent, mineral aggregate, and 

mineral filler. 

Recycled Rubber Product: Products which contain 

recycled rubber. 

Reinforcement: Any material, usually rubber and 

fabric, vulcanized to the inside of a tire to add 

strength to the cord body at an injury. 

Reinforcement Repair: Repairs made to the casing 

when damage has extended through more than 25 

percent, but less than 75 percent of the tire body, 

requiring both hole-filling material and reinforcement 

units. 

Remanufactured Tire: A worn tire that has been 

properly inspected and/or repaired and has had new 

rubber applied bead-to-bead to extend its serviceable 

life (also referred to as a remolded tire). 

Repair Materials: Specifically designed materials 

(repair units, repair gums, cements) used during the 

repair process of a tire or a tube. 

Repaired Tire: A tire that has been injured by 

cuts, puncture or breaks, and which has been 

reconditioned to restore its strength for additional 

service. 

Replacement Tire: Any new tire other than those sold 

as original equipment. 
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Request for Proposal: The invitation or 

announcement a funding organization issues for 

suppliers to submit a bid (proposal) on providing 

a specific product or service for the funding 

organization.

Residence Time: The average length of time that 

a substance spends in a particular system, such as 

waste tires in cement kiln.

Retail Tire Vendor: A term used to describe retail 

outlets for tires. 

Retreadability: The ability of a tire casing to be 

retreaded and provide acceptable performance. 

Retreaded Tire: A casing to which a new tread 

rubber, and sometimes shoulder and sidewall rubber, 

has been vulcanized to extend the usable life of the 

tire. 

Reused Tire: A passenger car tire taken off the rim 

of a vehicle and placed on the rim of another vehicle 

without any repair or other form of alteration. 

Ribs: The part of a tire tread pattern created by 

grooves which run circumferentially around the tire. 

Rim: The metal support for the tire and tube assembly 

on the wheel. The beads of a tire are seated on the 

rim. 

Rip-Shear Shredders: A tire shredder designed to 

reduce a scrap tire to pieces. The size and shape of 

the tire piece is dependent on the processing action 

of the shredder (i.e., cutting blades, rotary shear or 

rip-shear). 

RMA: U.S. Rubber Manufacturers Association; The 

trade association which represents the United States 

tire manufacturers and the United States based 

manufacturers of non-tire rubber products. 

Road Hazard: Any road or highway condition or 

obstacle which can damage a tire. 

Rough Shred: A piece of a shredded tire that is larger 

than 2” x 2” x 2”, but smaller than 30” x 2” x 4”. 

Rubber: An elastomer, generally implying natural 

rubber, but used loosely to mean any elastomer, 

vulcanized and unvulcanized. By definition, rubber 

is a material that is capable of recovering from large 

deformations quickly and forcibly and can be, or 

already is modified to a state in which it is essentially 

insoluble in a boiling solvent. 

Rubber Latex: Refer to Latex. 

Rubber Modified Asphalt: A general term used to 

identify the incorporation of scrap tire rubber into 

asphalt paving materials (also refer to Crumb Rubber 

Modified Asphalt Concrete). 

Rubber Modified Asphalt Concrete (RUMAC): A 

pavement product made with rubber. The rubber acts 

as an aggregate, and is blended into asphalt cement 

along with the aggregate in quantities ranging up to 

three percent rubber. This process is also referred to 

as the Dry Process. 

Rubber Polymer Matrix: An interlaced “screen” 

comprised of cross-linked, bound rubber 

macromolecules.

Rubber Reclamation: The process of degradation 

of the rubber’s structure through the use of 

mechanical, thermal or chemical processes. 

Rubberized Asphalt: Refer to Crumb Rubber 

Modified Asphalt Concrete. 

RUMAC: Refer to Rubber Modified Asphalt 

Concrete. 

Run Flat: Tire damage resulting from operating 

with low or no air pressure, sometimes identified 

by repetitive liner cracking or discoloration. Also 

refers to a class of passenger car tires capable of 

safely operating without air pressure in event of 

air loss. 

Salt and Pepper Granules: Granulated rubber 

that was made from white wall tires. 

SAM: Stress Absorbing Membrane; A rubberized 

asphalt layer applied over existing pavement to 

retard fatigue cracking. 

SAMI: Stress Absorbing Membrane Interlayers; A 

rubberized asphalt layer applied over an existing 

surface before application of a surface asphalt 

concrete used to retard reflective cracking. 

Scrap Pile Analysis: The inspection of tires in a 

scrap pile of a commercial account to determine 

causes of tire failures. 

Scrap Tire: A tire which can no longer be used for its 

original purpose due to wear or damage. 

Scrap Tire Pile: An accumulation of whole or 

processed scrap tires. 

Scrap Tire Processing: Any method of size reducing 

whole scrap tires to facilitate recycling, energy 

recovery or disposal. 
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Screen: An apparatus for separating sizes of granules. 

Secondary Material: Fragments or finished products 

or leftovers from a manufacturing process which 

converts a primary material into a commodity of 

economic value. 

Section Repair: Repairs made to the casing when an 

injury has extended through the tread or sidewall of a 

tire. The damaged cord is removed and replaced by a 

repair unit. 

Sectioned Tire: A tire that has been cut into at least 

two parts. 

Shoulder: The part of a tire between the tread and 

the sidewall. 

Shred: A cut or torn piece of scrap tire which is 

usually relatively small and may or may not be 

uniform. 

Shred Sizing: A term which generally refers to 

the process of cut tire pieces passing through a 

rated screen opening rather than those which are 

retained on the screen. Examples of which are: 

1” x 1”: A size reduced scrap tire with all 

dimensions one inch maximum. 

2” x 2”: A size reduced scrap tire, 2” x 2” x 2” 

maximum.

2” minus: Size reduced scrap tires, the 

maximum size of any piece has a dimension no 

larger than one inch, but 95 percent of which 

is less than X inches in any dimension (i.e., I” 

minus; 2” minus; 3” minus, etc.).

Shredded Tire: A size reduced scrap tire. 

The reduction in size was accomplished by a 

mechanical processing device commonly referred 

to as a “shredder”. 

Shredder: A machine used to reduce whole tires to 

pieces. 

Shredded Rubber: Pieces of scrap tires resulting 

from mechanical processing. 

Singulator: A conveyor that receives randomly 

oriented articles and positions those articles in single 

file. The conveyor includes skewed rollers for driving 

articles longitudinally and laterally against a side wall.

Sink Holes: An event that occurs in shredded scrap 

tire piles that develop as material under the surface is 

consumed in an internal fire, and the surface caves in. 

Sidewall: The side of a tire between the tread 

shoulder and the rim bead. 

Side-Dump Railcar: Type of railcar used for transport 

of materials. The railcar is tilted on its side to empty it 

and ensure complete removal of materials.

Sieve: An apparatus for separating sizes of materials 

(also refer to Screen). 

Single Pass Slued: A shredded tire that has been 

processed with a shear type shredder and the piece 

has not been classified. 

Sipes: Small cuts purposely made in the surface of a 

tread to improve traction. 

Size Reduction: Refers to cutting, shredding or other 

methods of reducing the size of, usually, a whole 

scrap tire.

Skid Resistance: The ability of the road surface and 

the tread to prevent the loss of tire traction. 

Skiving: The removal of damaged material prior to 

malting a repair. 

Sludge: Any of various more or less mud-like deposits 

or mixtures. Heavy, slimy deposit, sediment, or 

mass, as the waste resulting from various industrial 

operations.

Slurry: A thin mixture of an insoluble substance, as 

cement, clay, or coal, with a liquid, as water or oil.

Source Reduction: Any of a series of practices which 

act to reduce the number of scrap tires generated 

annually. These practices include, but are not limited 

to, using longer mileage tires; maintaining proper 

inflation; rotating tires; balancing tires; maintaining 

alignment; repairing tires and retreaded tires. 

Speed Rating: Maximum speed capabilities of new 

passenger and light truck tires are indicated by means 

of a speed symbol. 

Specifications: Written requirements for processes, 

materials or equipment. 

Speculative Accumulation: The stockpiling of scrap 

tires without the benefit of a business or business 

plan, but with the expectation that a market will be 

found. 

Split Rubber: A process in which tread is stripped 

from a tire for subsequent processing. 

Spontaneous Combustion: A term often used to 

explain the cause of internal, processed scrap tire 
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Glossary Scrap Tires:

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fires. This is an inappropriate use of the term. (Refer to 

Spontaneous Ignition.) 

Spontaneous Ignition: Heat generated by a chemical 

or bacterial action in a combustible material. 

Squirrel Foot: Exposed, rough pieces of belt or head 

wire (also refer to Fish Hooks). 

Steel Belt: Rubber coated steel cords that run 

diagonally under the tread of steel radial tires and 

extend across the tire approximately the width of 

the tread. The stiffness of the belts provides good 

handling, improved tread wear, and penetration 

resistance. 

Steel Belted Radial: A radial tire made with steel 

belts as opposed to textile belts. 

Stockpile: A storage pile of materials which is usually 

large and gradually accumulated. The material is 

sometimes accumulated for possible future use.

Structural Plies: Body and belt plies that contribute 

to casing strength. 

Substrate: A supporting material on which 

something else is formed or constructed.

Sump: A low area into which a liquid drains, for 

example a pit or reservoir.

Super-Single: Tires commonly found on off-road and 

dump equipment. They are a very tall, numerically 

high aspect ratio tires, as opposed to the “highway 

singles” which tend to have the same overall height as 

standard single tires.

Supplemental Fuel: A combustible material which 

displaces a portion of traditional fuel source. 

Surcharge: An extra fee or payment. An additional or 

excessive load or burden.

Surface Treatment: An application of bituminous 

material followed by a layer of mineral aggregate on a 

roadway. 

Synthetic Rubber: Rubber that is obtained by 

polymerizing petrochemical based monomers. 

Tactics: The method of securing the objectives laid 

out in a strategy through the use of personnel and 

equipment to achieve optimum results. 

Take-Off Tire: A tire that has been removed from 

a vehicle’s rim. This includes tires that are used, are 

candidate casings for repair, retreading, and to be 

scraped. 

Tax Map: An official map showing the boundary lines 

of properties and parcel dimensions for tax purposes. 

TDF: Refer to Tire Derived Fuel. 

Thermoplastic: A material with the capability 

(property) of being repeatedly softened by an 

increase of temperature and hardened by a decrease 

in temperature. 

Thermoset: The capability of maintaining a physical 

state across a wide range of temperatures. 

Thermoset Plastic: A solid macromolecular 

material which is incapable of continuous inelastic 

deformation by raising the temperature without 

chemical decomposition. 

Thermosetting: The property of a substance 

which undergoes a chemical change when heated, 

whereby a hardened non-thermoplastic product is 

formed. 

Three Dimensional Fire: A fire occurring within 

a material that has three surfaces. In the case of 

scrap tire fires, fire would be present on the upper 

surface, interior section and the bottom of the 

tire. 

Tipping Fee: Amounts charged by a facility 

operator for disposing of a scrap tire, or other 

waste, at that facility or landfill (also referred to as 

Disposal Fee). 

Tire: A continuous solid or pneumatic rubber 

covering encircling the wheel of a vehicle. 

Tire and Rim Association Inc.: A U.S. industrial 

association of tire, rim and wheel manufacturers 

which provides tire, rim and wheel standards. 

Tire Bounty: An amount paid for the collection 

and retrieval of illegally dumped or stockpiled scrap 

tires. 

Tire Buffings: Refer to Buffings. 

Tire Chip: A classified scrap tire that has a basic 

geometrical shape, which is generally two inches or 

smaller and has most of the wire removed (also refer 

to Chipped Tire). 

Tire Dealer: A term used to define independent retail 

tire vendors. 

Tire-Derived Fuel (TDF): Whole scrap tires or a 

uniformly shredded product obtained from whole 

tires, used as a fuel. 
G-14

Glossary Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

Tire Jockey: An independent business that hauls 

scrap tires for a fee from retail tire vendors to another 

location. Also known as a Casing Jockey. 

Tire Maintenance: The practice of establishing and 

ensuring proper air inflation, tire rotation, balancing, 

and alignment. 

Tire Rotation: The repositioning of the tires on a 

vehicle periodically to extend tire tread life. 

Top Retreading: Only the top, or tread area, is 

buffed away during the retread process and a tread 

rubber with abrupt shoulders is applied. This type of 

retreading is usually requested when tires are used 

in highway service where a special shoulder is not 

required and when appearance is secondary. 

Transformation: The process of incineration, 

pyrolysis, gasification, chemical and/or biological 

conversion of a scrap tire. 

Tread: That portion of the tire which contacts the 

road. 

Tread Buffing: Refer to Buffings. 

Tread Depth: The measurement from the tread 

surface to the bottom of the grooves. 

Tread Depth Gauge: An instrument used to 

measure the depth of a tire’s tread grooves. 

Tread Design: The non-skid pattern design on the 

tread portion of a tire. 

Tread Life: The length of service in miles or hours 

of operation before the tread wears out. 

Tread Peels: Refer to Buffings. 

Tread Rubber: Compounded, natural or synthetic 

rubber which is placed on a buffed casing and 

vulcanized to it to provide a new wearing surface. 

Tread Shaving: The shaving of tread from a tire 

with a blade (usually to half the original tread 

depth) to reduce tread squirm and tearing in racing 

applications. 

Tread Wear Indicators: Narrow bars of rubber 

molded at a height of 2/32nds of an inch across the 

bottom of the tread grooves. When the tread wears 

down to these bars, the tire should be replaced. The 

legal limits of a tire is 3/32nd of an inch of tread. 

Trommel: A mechanical device that sorts size reduced 

scrap tires. 

Truck Tire: Tires with a rim diameter of 20 inches or 

larger. 

Tubeless: A pneumatic tire that does not require an 

inner tube for air retention. 

Tube-Type: A pneumatic tire that requires an inner 

tube for air retention. 

Two Dimensional Fire: Fires that occur in a flat plane 

as in flammable liquid or processed scrap tire fires. 

Type A TDA: Tire derived aggregate in which pieces 

are a maximum of 75 mm (3 inches).

Type B TDA: Tire derived aggregate in which pieces 

range in size from 75 – 300 mm (12 inches). 

Undercure: A condition in which complete 

vulcanization was not achieved. 

Underinflation: A condition in which a tire is inflated 

below the recommended pressure, resulting in 

sluggish response, greatly increased tread wear, 

reduced gas mileage and casing failure. 

Uniformity: A measure of the tire’s ability to run 

smoothly and vibration free. 

Unmanaged Site: A scrap tire pile or facility where 

tires are stored that are not in compliance with the 

appropriate regulations or at a dump site where 

scrap tires are stockpiled with no intention of reuse, 

recycling or processing. 

Used Tire: A tire removed from a vehicle’s rim which 

cannot be legally described as new, but which is 

structurally intact and has a tread depth greater 

than the legal limit. This tire can be remounted onto 

another vehicle’s rim without repair. 

Valve: A device used to admit, retain, check or 

exhaust air in a tube or mounted tubeless tire. 

Velcro Effect: The interlocking of wire protruding 

from tire chips. 

Venting: An operation in which bias tires are 

punctured before retreading to guard against trapped 

air which causes casing separation. 

Virgin Material: Raw material, such as crude oil or 

aggregate taken from a quarry, that has not been 

previously used in any manufacturing process. 

Void: The space between aggregate tire pieces 

expressed as a percent of the total space occupied by 

the tire shreds.
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Glossary Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

Vulcanization: An irreversible process in which the 

chemical structure of rubber is changed (cross linked 

with sulfur) to become less plastic (sticky, putty-like) 

and more elastic (bouncy) (also refer to Curing). 

Vulcanized Rubber: The product of vulcanization 

in which rubber which has been chemically reacted 

with sulfur and accelerators (or other acceptable 

materials) under suitable conditions to achieve 

modified physical properties over a wide range of 

temperatures. 

Vulcanizing Agent: Any material that can produce 

in rubber the change in physical properties known as 

vulcanization, such as sulfur, peroxides, polysulfides, 

etc. 

Vulcanizing Cement: A rubber cement used to bond 

the new rubber to the old tire. 

Waste Tire: A tire which is no longer capable of being 

used for its original purpose, but which has been 

disposed of in such a manner that it cannot be used 

for any other purpose. 

Weather Checking: Fine cracks in the sidewall surface 

of a tire caused by oxidation and other atmospheric 

effects. 

Weaving: Refer to Laced Tires. 

Wet Bulb Globe Temperature: A composite 

temperature used to estimate the effect of 

temperature, humidity, wind speed (wind chill) 

and solar radiation on humans. It is to determine 

appropriate exposure levels to high temperatures.

Wet Process: Any method that blends ground rubber 

with the asphalt cement prior to incorporating the 

binder in the asphalt paving project. 

Wheel Alignment: Adjustment of wheel ends and 

axles to ensure the proper orientation of the tires to 

the chassis and to each other. This ensures the vehicle 

and the tires roll in a straight line. 

Whole Tire: A scrap tire that has been removed from 

a rim, but which has not been processed. 

Wild Rubber: Rubber collected from trees growing 

wild in nature as opposed to trees cultivated on 

plantations. 

Wires: High tensile, brass plated steel wires, coated 

with a special adhesion-promoting compound that 

are used as tire reinforcement. Belts of radial tires plies 

and beads are common uses. 

Wobble: A performance irregularity in tire and wheel 

assemblies characterized by a side to side motion. 

Worn Tire: Any tire which has been removed from a 

vehicle because of wear or damage. Worn tires can be 

retreaded, repaired or scrapped. 

Zipper: Circumferential rupture of sidewall body 

cables.

A-1

Appendix A Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

APPENDIX A

TDA Material Specifications

TDA, GENERAL

The material shall be made from scrap tires which 

shall be shredded into the sizes specified herein. 

They shall be produced by a shearing process. TDA 

produced by a hammer mill will not be allowed. The 

TDA shall be free of all contaminants such as oil, 

grease, gasoline, diesel fuel, etc., that could leach into 

the groundwater or create a fire hazard. In no case 

shall the TDA contain the remains of tires that have 

been subjected to a fire because the heat of a fire 

may liberate liquid petroleum products from the tire 

that could create a fire hazard when the shreds are 

placed in a fill. The TDA shall be free from fragments of 

wood, wood chips, and other fibrous organic matter. 

The TDA shall have less than 1 percent (by weight) of 

metal fragments that are not at least partially encased 

in rubber. Metal fragments that are partially encased 

in rubber shall protrude no more than 25 mm (1 inch) 

from the cut edge of the TDA on 75 percent of the 

pieces (by weight) and no more than 50 mm (2 inch) 

on 90 percent of the pieces (by weight). The gradation 

shall be measured in accordance with C136-05 (also 

designated AASHTO T-27), “Standard Method for Sieve 

Analysis of Fine and Coarse Aggregate,” except that 

the minimum sample size shall be 6 to 12 kg (15 to 25 

lbs) for Type A TDA and 16 to 23 kg (35 to 50 pounds) 

for Type B TDA.

TDA, TYPE A

Type A TDA shall have a maximum dimension, 

measured in any direction, of 203 mm (8 inch). In 

addition, Type A TDA shall have 100 percent passing 

the 102 mm (4 inch) square mesh sieve, a minimum 

of 95 percent passing (by weight) the 75 mm (3 inch) 

square mesh sieve, a maximum of 50 percent passing 

(by weight) the 38 mm (1.5 inch) square mesh sieve, 

and a maximum of 5 percent passing (by weight) the 

No. 4 sieve.

TDA, TYPE B

A minimum of 90 percent (by weight) shall have a 

maximum dimension, measured in any direction, 

of 300 mm (12 inch) and 100 percent shall have a 

maximum dimension, measured in any direction, 

of 450 mm (18 inch). At least one side wall shall be 

severed from the tread of each tire. A minimum of 75 

percent (by weight) shall pass the 203 mm (8 inch) 

square mesh sieve, a maximum of 50 percent (by 

weight) shall pass the 76 mm (3-inch) square mesh 

sieve, a maximum of 25 percent (by weight) shall 

pass the 38 mm (1.5-inch) square mesh sieve, and 

a maximum of 1 percent (by weight) shall pass the 

No. 4 sieve (4.75 mm; 0.187 inch).
A-2

Appendix B Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

APPENDIX B

Design Guidelines to Minimize Internal 

Heating of Tire Shred Fills

(JULY 1997; REVISED 2003)

BACKGROUND

Since 1988 more than 70 tire shred fills with a 

thickness less than 1 m and an additional ten fills 

less than 4 m thick have been constructed. In 1995 

three tire shred fills with a thickness greater than 

8 m experienced a catastrophic internal heating 

reaction. These unfavorable experiences have 

curtailed the use of all tire shred fills on highway 

projects.

Possible causes of the reaction are oxidation of the 

exposed steel belts and oxidation of the rubber. 

Microbes may have played a role in both reactions. 

Although details of the reaction are under study, 

the following factors are thought to create 

conditions favorable for oxidation of exposed 

steel and/or rubber: free access to air; free access 

to water; retention of heat caused by the high 

insulating value of tire shreds in combination with 

a large fill thickness; large amounts of exposed 

steel belts; smaller tire shred sizes and excessive 

amounts of granulated rubber particles; and the 

presence of inorganic and organic nutrients that 

would enhance microbial action.

The design guidelines given in the following 

sections were developed to minimize the 

possibility for heating of tire shred fills by 

minimizing the conditions favorable for this 

reaction. As more is learned about the causes of 

the reaction, it may be possible to ease some of 

the guidelines. In developing these guidelines, the 

insulating effect caused by increasing fill thickness 

and the favorable performance of projects with tire 

shred fills less than 4 m thick were considered. Thus, 

design guidelines are less stringent for projects with 

thinner tire shred layers. The guidelines are divided 

into two classes: Class I Fills with tire shred layers 

less than 1 m thick and Class II Fills with tire shred 

layers in the range of 1 m to 3 m thick. Although 

there have been no projects with less than 4 m of 

tire shred fill that have experienced a catastrophic 

heating reaction, to be conser¬vative, tire shred 

layers greater than 3 m thick are not recommended. 

In addition to the guidelines given below, the 

designer must choose the maximum tire shred size, 

thickness of overlying soil cover to address pavement 

structural concerns, etc., to meet the requirements 

imposed by the engineering performance of the 

project. The guidelines are for use in designing tire 

shred monofills. Design of fills that are mixtures or 

alternating layers of tire shreds and mineral soil that is 

free from organic matter should be handled on a case 

by case basis.

GENERAL GUIDELINES FOR ALL TIRE 

SHRED FILLS

All tires shall be shredded such that the largest shred 

is either: (1) no greater than 0.6 m in any direction 

measured, or (2) no more than one-quarter of the 

circumference of the tire, whichever is less. At least 

one sidewall shall be severed from the tire shred.

 The tire shreds shall be free of all contaminates such 

as oil, grease, gasoline, diesel fuel, etc., that could 

create a fire hazard. In no case shall the tire shreds 

contain the remains of tires that have been subjected 

to a fire because the heat of a fire may liberate liquid 

petroleum products from the tire that could create a 

fire hazard when the shreds are placed in a fill.

CLASS I FILLS

Material Guidelines

The tire shreds shall have a maximum of 50 percent 

(by weight) passing the 38-mm sieve and a maximum 

of 5 percent (by weight) passing the 4.75-mm sieve.

Design Guidelines

No design features are required to minimize heating 

of Class I Fills.

CLASS II FILLS

Material Guidelines

The tire shreds shall have a maximum of 25 percent 

(by weight) passing the 38-mm sieve and a maximum 

of 1 percent (by weight) passing the 4.75-mm sieve. 
A-3

Appendix B Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

The tire shreds shall be free from fragments of wood, 

wood chips, and other fibrous organic matter. The 

tire shreds shall have less than 1 percent (by weight) 

of metal fragments which are not at least partially 

encased in rubber. Metal fragments that are partially 

encased in rubber shall protrude no more than 25 mm 

from the cut edge of the tire shred on 75 percent of 

the pieces and no more than 50 mm on 100 percent 

of the pieces.

Design guidelines. The tire shred fill shall be 

constructed in such a way that infiltration of water 

and air is minimized. Moreover, there shall be no 

direct contact between tire shreds and soil containing 

organic matter, such as topsoil. One possible way 

to accomplish this is to cover the top and sides 

of the fill with a 0.5 m thick layer of compacted 

mineral soil with a minimum of 30 percent fines. 

The mineral soil should be free from organic matter 

and should be separated from the tire shreds with a 

geotextile. The top of the mineral soil layer should 

be sloped so that water will drain away from the tire 

shred fill. Additional fill may be placed on top of 

the mineral soil layer as needed to meet the overall 

design of the project. If the project will be paved, it 

is recommended that the pavement extend to the 

shoulder of the embankment or that other measures 

be taken to minimize infiltration at the edge of the 

pavement.

Use of drainage features located at the bottom of 

the fill that could provide free access to air should be 

avoided. This includes, but is not limited to, open 

graded drainage layers daylighting on the side of 

the fill and drainage holes in walls. Under some 

conditions, it may be possible to use a well graded 

granular soil as a drainage layer. The thickness of 

the drainage layer at the point where it daylights 

on the side of the fill should be minimized. For tire 

shred fills placed against walls, it is recommended 

that the drainage holes in the wall be covered with 

well graded granular soil. The granular soil should 

be separated from the tire shreds with geotextile.

GENERAL GUIDELINES FOR ALL TIRE SHRED FILLS (July 1997; revised 2003)

All tires shall be shredded such that the largest shred is either: (1) no greater than 0.6 m in any direction measured, or (2) 

no more than one-quarter of the circumference of the tire, whichever is less. At least one sidewall shall be severed from 

the tire shred.

Tire shreds shall be free of contaminates such as oil, grease, gasoline, diesel fuel, etc., that could create a fire hazard

In no case shall the tire shreds contain the remains of tires that have been subjected to a fire

CLASS I FILLS ( < 1 m thick)

Maximum of 50 percent (by weight) passing 38-mm sieve

Maximum of 5 percent (by weight) passing 4.75-mm sieve

CLASS II FILLS (1-3 m thick)

Maximum of 25 percent (by weight) passing 38-mm sieve

Maximum of 50 percent (by weight) passing 50-mm sieve

Maximum of 1 percent (by weight) passing 4.75-mm sieve

Tire shreds shall be free from fragments of wood, wood chips, and other fibrous organic matter

The tire shreds shall have less than 1 percent (by weight) of metal fragments that are not at least partially encased in 

rubber

Metal fragments that are partially encased in rubber shall protrude no more than 25 mm from the cut edge of the tire 

shred on 75 percent of the pieces by weight and no more than 50 mm on 90 percent of the pieces by weight

Infiltration of water and air into the tire shred fill shall be minimized

No direct contact between tire shreds and soil containing organic matter, such as topsoil

Tire shreds should be separated from the surrounding soil with a geotextile

Use of drainage features located at the bottom of the fill that could provide free access to air should be avoided 
A-4

Appendix C Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

APPENDIX C

Engineering Properties of TDA

Selected engineering properties of tire derived 

aggregate (TDA) are presented in this appendix. This 

information includes gradation, compacted unit 

weight, compressibility, time-dependent settlement, 

and shear strength.

GRADATION

Large pieces are desirable when the TDA zone is 

more than 1 m (3.3 feet) thick because they are 

less susceptible to self-heating (as discussed in 

Appendix B). However, when the TDA contain a 

significant number of pieces larger than 300 mm 

(12 inches), they tend to be difficult to spread in a 

uniform lift thickness. Thus, a typical specification 

requires that a minimum of 90 percent (by weight) 

of the TDA have a maximum dimension, measured 

in any direction, of less than 300 mm (12 inches) 

and that 100 percent of the TDA have a maximum 

dimension less than 450 mm (18 inches). 

Moreover, at least 75 percent (by weight) must 

pass a 200-mm (8-inch) sieve and at least one 

sidewall must be severed from the tread of each 

tire. To minimize the quantity of small pieces, which 

can be susceptible to self-heating, the specifications 

require that no more than 50 percent (by weight) 

pass the 75-mm (3-inch) sieve, 25 percent (by weight) 

pass the 38-mm (1.5-inch) sieve, and no more than 1 

percent (by weight) pass the No. 4 (4.75-mm) sieve. 

Pieces of this size are commonly referred to as Type 

B TDA. When samples are collected for gradation 

analysis, they should be collected directly from the 

discharge conveyor of the processing machine. This 

procedure ensures that the minus No. 4 fraction will 

be representative, which is not the case when samples 

are collected by shoveling pieces from a stockpile. 

TDA that meets the size requirements given above 

generally have a uniform gradation. Typical results 

are shown in Exhibit C-1.

 COMPACTED UNIT WEIGHT

The compacted unit weight of TDA has been 

investigated in the laboratory for pieces up to 75 

mm (3 inches). These tests were generally done with 

254-mm (10-inches) or 305-mm (12-inches) inside 

Exhibit C-1. Gradation of Type B TDA used as lightweight fill for Portland Jetport Interchange 

BOULDERS GRAVEL SAND FINES

1e+003 100 10 1 0.1 0.01

GRAIN DIAMETER (mm)

0

10

20

30

40

50

60

70

80

90

100

PERCENT

P

A

S

SIN

G
A-5

Appendix C Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

diameter compaction molds and impact compaction. 

Compacted dry unit weights ranged from 0.61 to 0.69 

Mg/m3 (38 to 43 pcf) (Ref.1). 

The effect of compaction energy and compaction 

water content was investigated. Increasing the 

compaction energy from 60 percent of standard 

Proctor to 100 percent of modified Proctor increased 

the compacted unit weight by only 0.02 Mg/m3 (1.2 

pcf), showing that compaction energy has only a 

small effect on the resulting unit weight. Unit weights 

were about the same for air-dried samples and 

samples at saturated surface dry conditions (about 4 

percent water content), indicating that water content 

has a negligible effect on unit weight (Refs. 7, 11). 

One significance of this finding is that there is no 

need to control moisture content of TDA during field 

placement.

Measuring the compacted unit weight of TDA with 

a 300-mm (12-inches) maximum size is impractical 

in the laboratory. However, results from a highway 

embankment constructed with large TDA suggest 

that the unit weight of 300-mm (12-inches) maximum 

size TDA is less than for 75-mm (3-inches) maximum 

size TDA (Ref. 10). 

COMPRESSIBILITY

The compressibility of TDA with a 75 mm (3 

inches) maximum size has been measured in the 

laboratory. An apparatus used by Nickels (Ref. 

12) had a 356-mm (14-inches) inside diameter 

and could accommodate a sample up to 356-mm 

(14-inches) thick. One challenge to measuring 

the compressibility of TDA is friction between 

the TDA and the inside wall of the test container. 

The apparatus used by Nickels (Ref. 12) uses load 

cells to measure the load carried by the specimen 

both at the top and bottom of the sample, as 

shown in Exhibit C-2. Even though Nickels used 

grease to lubricate the inside of the container, up 

to 20 percent of the load applied to the top of the 

sample was transferred to the walls of the container 

by friction. Compressibility of TDA with a 75 mm (3 

inches) maximum size is shown in Exhibit C-3. The 

initial unit weights ranged from 0.51 to 0.64 Mg/

m3 (32.1 to 40.1 pcf). There is a general trend of 

decreasing compressibility with increasing initial 

unit weight. The results for tests MD1 and MD4 are 

most applicable to using TDA as lightweight fill since 

their initial unit weight is typical of field conditions. 

Compressibility for stresses up to 480 kiloPascals (kPa) 

(70 pounds per square inch [psi]) are given by Manion 

and Humphrey (Ref. 11) and Humphrey and Manion 

Exhibit C-2. Compressibility apparatus used by Nickels (Ref. 12)
A-6

Appendix C Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

(Ref. 7). Laboratory data on the compressibility 

of TDA with a maximum size greater than 75 

mm (3 inches) are not available; however, field 

measurements indicate that TDA with a 300-mm 

(12-inches) maximum size are less compressible 

than smaller TDA.

TIME-DEPENDENT SETTLEMENT

TDA exhibits a small amount of time-dependent 

settlement. Time-dependent settlement of thick 

TDA fills was measured by Tweedie and others 

(1997). Three types of TDA were tested with 

maximum sizes ranging from 38 to 75 mm (1.5 

to 3 inches). The fill was 4.3 m (14 feet) thick 

and was surcharged with 36 kPa (750 psf), which is 

equivalent to about 1.8 m (6 feet) of soil. Vertical 

strain versus elapsed time is shown in Exhibit C-4. It 

is seen that time-dependent settlement occurred 

for about 2 months after the surcharge was placed. 

During the first 2 months, about 2 percent vertical 

strain occurred, which is equivalent to more than 75 

mm (3 inches) of settlement for this 4.3-m (14-feet)-

thick fill. The measurements are in general agreement 

with time-dependent laboratory compressibility tests 

conducted by Humphrey and others (Ref. 7). When 

TDA is used as backfill behind a pile supported bridge 

abutment or other structures that will experience 

little settlement, it is important to allow sufficient 

time for most of the time-dependent settlement of 

the TDA to occur before final grading and paving. 

Time-dependent settlement is of less concern when 

the ends of the TDA fill can be tapered from the full 

thickness to zero over a reasonable distance. 

 SHEAR STRENGTH

The shear strength of TDA has been measured using 

direct shear and triaxial shear apparatus. The large 

TDA typically used for civil engineering applications 

requires that specimen sizes be several times larger 

than are used for common soils. This method has 

generally been used for TDA 25 mm (1inch) in size 

and smaller because of the limited availability of 

large triaxial shear apparatus. Moreover, the triaxial 

shear apparatus is generally not suitable if steel belts 

protrude from the cut edge of the TDA since the 

wires puncture the membrane used to surround the 

specimen.

The shear strength of TDA has been measured using 

triaxial shear (Refs. 2, 3, 4, 8); and using direct shear 

(Refs.5, 6, 7, 8, 9). Failure envelopes determined from 

direct shear and triaxial tests for TDA with a maximum 

size ranging from 9.5 to 900 mm (0.37 to 35 inches) 

are shown in Exhibit C-5. Data from Gebhard and 

others (Ref. 6) on larger size TDA fall in the same 

range. Available data suggest that shear strength 

is not affected by TDA size. Moreover, results from 

triaxial and direct shear tests are similar. Overall, 

the failure envelopes appear to be concave down. 

Thus, best fit linear failure envelopes are applicable 

only over a limited range of stresses. Friction angles 

and cohesion intercepts for linear failure envelopes 

for the data shown in Exhibit C-5 are given in Table 

C-1. TDA requires sufficient deformation to mobilize 

its strength (Ref. 8). Thus, a conservative approach 

should be taken when choosing strength parameters 

for TDA embankments founded on sensitive clay 

foundations.

0 1 2 3 4 5 6 7 8 9

Average Vertical Stress (psi)

0

5

10

15

20

25

30

35

40

Vertical Strain (%)

Legend Title

Humphrey et al. (1992)-Not Recorded

Test NY2 - 32.1 pcf

Test NY3 - 32.4 pcf

Test NY4 - 37.3 pcf

Test NY5 - 37.2 pcf

Test MD1 - 40.1 pcf

Test MD2 - 36.5 pcf

Test MD3 - 38.0 pcf

Test MD4 - 39.6 pcf

0

5

10

15

20

25

30

35

40

Exhibit C-3. Compressibility of TDA with a 3-inches (75-mm) 

maximum size (Ref. 12)

Exhibit C-4. Time-dependent settlement of TDA subjected to a surcharge of 

750 psf (36 kPa) (Ref. 13)
A-7

Appendix C Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

Exhibit C-5. Failure envelopes for TDA with maximum sizes ranging from 0.37 to 3 inches (9.5 to 75 mm)

Table C-1. Strength parameters for TDA.

Supplier

Maximum shred size Test 

method

Applicable range of 

normal stress Φ Cohesion intercept

inches mm psf kPa deg. psf kPa

F&B 0.5 38 D.S. 360 to 

1300

17 to 62 25 180 8.6

Palmer 3 75 D.S. 360 to 

1300

17 to 62 19 240 11.5

Pine State 3 75 D.S. 360 to 

1400

17 to 68 21 160 7.7

Pine State 3 75 D.S. 310 to 900 15 to 43 26 90 4.3

Dodger 35 900 D.S. 120 to 580 5.6 to 28 37 0 0

Unknown 0.37 9.5 Triaxial 1100 to 

1700

52 to 82 24 120 6.0

Unknown 0.37 9.5 Triaxial 230 to 400 11 to 19 36 50 2.4

Note: D.S. = Direct Shear
A-8

Appendix C Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

References

1. ASTM International. 1998. “Standard Practice 

for Use of Scrap Tires in Civil Engineering 

Applications.” ASTM D6270-98, ASTM 

International. W. Conshohocken, Pennsylvania.

2. Ahmed, I. 1993. “Laboratory Study on Properties 

of Rubber Soils,” Report No. FHWA/IN/JHRP-93/4, 

School of Civil Engineering, Purdue University, 

West Lafayette, Indiana.

3. Benda, C.C. 1995. “Engineering Properties of 

Scrap Tires Used in Geotechnical Applications,” 

Report 95-1, Materials and Research Division, 

Vermont Agency of Transportation, Montpelier, 

Vermont.

4. Bressette, T. 1984. “Used Tire Material as an 

Alternative Permeable Aggregate.” Report No. 

FHWA/CA/TL-84/07, Office of Transportation 

Laboratory, California Department of 

Transportation, Sacramento, California.

5. Cosgrove, T.A. 1995. “Interface Strength 

between Tire Chips and Geomembrane for 

Use as a Drainage Layer in a Landfill Cover.” 

Proceedings of Geosynthetics’95, Industrial 

Fabrics Association, St. Paul, Minnesota Vol. 3, pp. 

1157-1168.

6. Gebhardt, M.A., Kjartanson, B.H., and 

Lohnes, R.A. 1998. “Shear Strength of Large 

Size Shredded Scrap Tires as Applied to the 

Design and Construction of Ravine Crossings.” 

Proceedings of the 4th International Symposium 

on Environmental Geotechnology and 

Global Sustainable Development, Danvers, 

Massachusetts.

7.Humphrey, D.N. and Manion, W.P. 1992. 

“Properties of Tire Chips for Lightweight Fill.” 

Proceedings of Grouting, Soil Improvement, and 

Geosynthetics, New Orleans, Louisiana, Vol. 2, pp. 

1344-1355.

8. Humphrey, D.N., and Sandford, T.C. 1993. “Tire 

Chips as Lightweight Subgrade Fill and Retaining 

Wall Backfill.” Proceedings of the Symposium 

on Recovery and Effective Reuse of Discarded 

Materials and By-Products for Construction 

of Highway Facilities, Federal Highway 

Administration, Washington, D.C., pp. 5-87 to 

5-99.

9. Humphrey, D.N., Sandford, T.C., Cribbs, M.M., 

and Manion, W.P. 1993. “Shear Strength and 

Compressibility of Tire Chips for Use as Retaining 

Wall Backfill.” Transportation Research Record 

No. 1422, Transportation Research Board, 

Washington, D.C., pp. 29-35.

10. Humphrey, D.N., Whetten, N., Weaver, J., Recker, 

K., and Cosgrove, T.A. 1998. “Tire TDA as 

Lightweight Fill for Embankments and Retaining 

Walls.” Proceedings of the Conference on 

Recycled Materials in Geotechnical Applications, 

C. Vipulanandan and D. Elton, eds., ASCE, pp. 51-

65.

11. Manion, W.P., and Humphrey, D.N. 1992. “Use 

of Tire Chips as Lightweight and Conventional 

Embankment Fill, Phase I - Laboratory.” Technical 

Paper 91-1, Technical Services Division, Maine 

Department of Transportation, Augusta, Maine.

12. Nickels, W.L., Jr. 1995. “The Effect of Tire Chips 

as Subgrade Fill on Paved Roads.” M.S. Thesis, 

Department of Civil Engineering, University of 

Maine, Orono, Maine, 215 pp.

13. Tweedie, J.J., Humphrey, D.N. and Sandford, 

T.C. 1997. “Tire Chips as Lightweight Backfill for 

Retaining Walls - Phase II,” A Study for the New 

England Transportation Consortium, Department 

of Civil and Environmental Engineering, 

University of Maine, Orono, Maine, 291pp.?
A-9

Appendix D Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

APPENDIX D

Calculation of Final In-Place Unit Weight 

and Overbuild

Final In-Place Unit Weight

The final in-place unit weight of the tire-derived 

aggregate (TDA) must be estimated during design. 

This unit weight is a necessary input for slope stability 

analysis and analysis of the stability of retaining 

walls. Estimation of the in-place unit weight must 

consider the immediate compression of the TDA 

under its self-weight and the weight of overlying 

soil and pavement. The calculation procedure is 

straightforward and is outlined below:

Step 1. From laboratory compaction tests or typical 

values, determine the initial uncompressed, 

compacted dry unit weight of TDA (γdi) (for Type 

A TDA with a 75-mm [3-inches] maximum size, 

use 0.64 mg/m3 [40 pcf]).

Step 2. Estimate the in-place water content of TDA 

(w) and use the water content to determine the 

initial uncompressed, compacted total (moist) 

unit weight of TDA: γti = γdi (1+w). Unless better 

information is available, use w = 3 or 4 percent.

Step 3. Determine the vertical stress in center of TDA 

layer (σv-center). To calculate the vertical stress, 

hypothesize the compressed unit weight of TDA 

(γtc) (0.80 Mg/m3 (50 pcf) is suggested for the first 

test).

σv-center = tsoil(γt-soil) + (tTDA/2)(γtc)

where: tsoil = thickness of overlying soil layer

γt-soil = total (moist) unit weight of overlying soil

t

TDA = compressed thickness of TDA layer

(Note: In the equation, the thickness of the TDA 

layer is divided by 2 since the stress in the center of 

the layer is being computed.)

Step 4. Determine the percent compression (εv

) 

using σv-center and the measured laboratory 

compressibility of the TDA; for TDA with a 75-mm 

(3-inches) maximum size, use the results for test 

MD1 or MD4 in Exhibit D-1.

Step 5. Determine the compressed moist unit weight 

of the TDA: γtc = γti/(1-εv

). If necessary, return to 

step 3 with a better estimate of the compressed 

moist unit weight.

This procedure was used to predict the compressed 

unit weight of a 4.3-m (14-feet) thick TDA fill 

covered by 1.8 m (6 feet) of soil built in Topsham, 

Maine. TDA with a 75-mm (3-inches) maximum 

size was used in the upper third of the fill, while 

TDA with a 150-mm (6-inches) maximum size was 

used in the lower part of the fill. The predicted 

compressed moist unit weight was 0.91 Mg/m3 (57 

pcf). The actual in-place unit weight calculated 

from the final volume of the TDA zone and the 

weight of TDA delivered to the project was also 

0.91 Mg/m3 (57 pcf). This validates the reliability 

of the laboratory compressibility tests and the 

procedure to estimate the compressed moist unit 

weight for TDA with maximum sizes between 75 

and 150 mm (3 and 6 inches). However, when 

the procedure was applied to TDA with a 300-mm 

(12-inches) maximum size, the predicted unit 

weight was greater than determined in the field. 

For a highway embankment built in Portland, 

Maine, with TDA with a 300-mm (12-inches) 

maximum size, the predicted compressed moist 

unit weight was 0.93 Mg/m3 (58 pcf) compared 

with an actual unit weight of 0.79 Mg/m3 (49 

pcf). The reasons for the difference appear to 

be a lower initial uncompressed unit weight and 

the lower compressibility for the larger TDA. It 

is recommended that the unit weight calculated 

using the procedure outlined above should be 

reduced by 15 percent for 300-mm (12-inches) 

maximum size TDA.

Calculation of Overbuild

TDA experiences immediate compression under an 

applied load, such as the weight of an overlying soil 

cover. The top elevation of the TDA layers should be 

overbuilt to compensate for this compression. The 

overbuild is determined using the procedure given 

below with the aid of a design chart (Exhibit D-2). The 

design chart was developed using a combination of 

laboratory compressibility tests and compression data 

measured from field projects. Exhibit D-2 is applicable 
A-10

Appendix D Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

to Type-B TDA (300-mm [12-inches] maximum size) 

that has been placed and compacted in 300-mm 

(12-inches)-thick layers. To use this procedure with 

smaller Type A TDA (3-inches maximum size), increase 

the calculated overbuild by 30 percent.

The overbuild for a single TDA layer is derived directly 

from Exhibit D-2. First, calculate the vertical stress 

that will be applied to the top of the TDA layer as the 

sum of the unit weights multiplied by the thicknesses 

of the overlying layers. Second, enter Exhibit D-2 

with the calculated vertical stress and the final 

compressed thickness of the TDA layer to find the 

overbuild. Consider the following example:

0.229 m pavement at 2.56 Mg/m3

0.610 m aggregate base at 2.00 Mg/m3

0.610 m low permeability soil cover at 1.92 Mg/m3

3.05-m (10 feet) thick TDA layer

The vertical stress applied to the top of the TDA 

layer would be:

(0.229 m x 2.56 Mg/m3 x 9.81 m/s2) + (0.610 m x 

2.00 Mg/m3 x 9.81 m/s2) + (0.610 m x 1.92 Mg/m3 

x 9.81 m/s2) = 29.1 kPa x 20.884 psf/kPa = 610 psf

Enter Exhibit D-2 with 610 psf (29.1 kPa) and using 

the line for a TDA layer thickness of 10 feet (3.05 m) 

results in an overbuild of 0.68 feet (0.21 m). Round 

to the nearest 0.1 m. Thus, an overbuild of 0.2 m is 

necessary.

The overbuild for the bottom TDA layer of a twolayer cross-section is also determined directly from 

Exhibit D-2. The procedure is the same as described 

above for a single TDA layer. Consider the following 

example:

0.229 m pavement at 2.56 Mg/m3

0.610 m aggregate base at 2.00 Mg/m3

0.610 m low permeability soil cover at 1.92 Mg/m3

3.05-m (10 feet) thick TDA layer at 0.80 Mg/m3

0.915 m soil separation layer at 1.92 Mg/m3

3.05-m (10 feet) thick lower TDA layer

 The vertical stress applied to the top of the TDA layer 

would be:

(0.229 m x 2.56 Mg/m3

 x 9.81 m/s2) + (0.610 m x 2.00 

Mg/m3 x 9.81 m/s2) + (0.610 m x 1.92 Mg/m3 x 9.81 m/

s2

) + (3.05 m x 0.80 Mg/m3 x 9.81 m/s2) + (0.915 m x 

Exhibit D-1. Compressibility of Type A TDA at low stresses (Ref. 1)

0 1 2 3 4 5 6 7 8 9

Average Vertical Stress (psi)

0

5

10

15

20

25

30

35

40

Vertical Strain (%)

Legend Title

Humphrey et al. (1992)-Not Recorded

Test NY2 - 32.1 pcf

Test NY3 - 32.4 pcf

Test NY4 - 37.3 pcf

Test NY5 - 37.2 pcf

Test MD1 - 40.1 pcf

Test MD2 - 36.5 pcf

Test MD3 - 38.0 pcf

Test MD4 - 39.6 pcf

0

5

10

15

20

25

30

35

40

(Note: 1 psi = 144 psf = 6.895 kPa)
A-11

Appendix D Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

1.92 Mg/m3 x 9.81 m/s2)= 70.4 kPa x 20.884 psf/kPa = 

1,470 psf

Enter Exhibit D-2 with 1470 psf (70.4 kPa) and using 

the line for a TDA layer thickness of 10 feet (3.05 m) 

results in an overbuild of 1.13 feet (0.34 m). Round to 

the nearest 0.1 m. Thus, the use of a 0.3-m overbuild 

for the lower TDA layer is needed.

The overbuild of the top elevation for the upper TDA 

layer of a two-layer cross-section must include both 

the compression of the upper TDA layer when the 

pavement, base, and soil cover is placed, and the 

compression of the lower TDA layer that will still occur 

under the weight of these layers. In other words, the 

lower TDA layer has not yet compressed to its final 

thickness. This final compression will only occur once 

the embankment reaches final grade. Therefore, the 

question is, “How much compression of the lower TDA 

layer will occur due to placing the pavement, base 

and soil cover?” Consider the same two-layer 

example used above.

0.229 m pavement at 2.56 Mg/m3

0.610 m aggregate base at 2.00 Mg/m3

0.610 m low permeability soil cover at 1.92 Mg/

m3

3.05-m (10 feet) thick TDA layer at 0.80 Mg/m3

0.915 m soil separation layer at 1.92 Mg/m3

3.05-m (10 feet) thick lower TDA layer

Step 1. The final vertical stress applied to the top of 

the upper TDA layer would be: (0.229 m x 2.56 Mg/

m3 x 9.81 m/s2) + (0.610 m x 2.00 Mg/m3 x 9.81 m/

s2) + (0.610 m x 1.92 Mg/m3 x 9.81 m/s2) = 29.1 kPa 

x 20.884 psf/kPa = 610 psf. Enter Exhibit D-2 with 

610 psf (29.1 kPa) and using the line for a TDA layer 

Exhibit D-2. Overbuild design chart for Type B TDA 

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Vertical stress applied to top of tire shred layer (psf)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

Overbuild (ft)

1 ft

2 ft

3 ft

4 ft

5 ft

6 ft

7 ft

8 ft

9 ft

Tire shred layer thickness = 10 ft
A-12

Appendix D Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

thickness of 10 feet (3.05 m) results in a compression 

of 0.68 feet (0.21 m).

Step 2. Once the upper TDA layer (but not the top 

soil cover) is in place, the vertical stress applied to the 

top of the lower TDA layer would be: (3.05 m x 0.80 

Mg/m3

 x 9.81 m/s2) + (0.915 m x 1.92 Mg/m3 x 9.81 m/

s2) = 41.1 kPa x 20.884 psf/kPa = 860 psf. To determine 

the compression of the lower TDA layer that has 

occurred up to this point, enter Exhibit D-2 with 

860 psf (41.1 kPa) and using the line for a TDA layer 

thickness of 10 feet (3.05 m) results in a compression 

of 0.84 feet (0.26 m).

Step 3. Once the embankment reaches its final 

grade, the vertical stress applied to the top of the 

lower TDA layer would be 70.4 kPa = 1470 psf, as 

calculated previously. Enter Exhibit D-2 with 1470 

psf (70.4 kPa) and using the line for a TDA layer 

thickness of 10 feet (3.28 m) results in an overbuild 

of 1.13 feet (0.34 m). (Note: rounding to 0.3 m 

would give the overbuild of the lower TDA layer.)

Step 4. Subtract the result from Step 2 from the 

result of Step 3 to obtain the compression of 

the lower TDA layer which will occur when the 

pavement, base, and soil cover is placed: 0.34 m – 

0.26 m = 0.08 m.

Step 5. Sum the results from Steps 1 and 4 to 

obtain the amount the top elevation of the upper 

TDA layer should be overbuilt. 0.21 m + 0.08 m 

= 0.29 m (0.95 feet). Round to the nearest 0.1 m. 

Thus, the elevation of the top of the upper TDA 

layer should be overbuilt by 0.3 m.

Final result: Overbuild the top elevation of the 

lower TDA layer by 0.3 m and the upper TDA layer 

by 0.3 m.

Reference

1. Nickels, W.L., Jr. 1995. “The Effect of Tire Chips 

as Subgrade Fill on Paved Roads.” M.S. Thesis, 

Department of Civil Engineering, University of 

Maine, Orono, Maine, 215 pp.
A-13

Appendix E Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

APPENDIX E

Case Histories – Use of TDA as Lightweight 

Embankment Fill

Case History – Portland Jetport 

Interchange

Tired derived aggregate (TDA) was used as 

lightweight fill for construction of two 9.8-m (32-feet)-

high highway embankments in Portland, Maine (Ref. 

5). These embankments were the approach fills to a 

new bridge over the Maine Turnpike. The bridge is 

part of a new interchange that provides better access 

to the Portland Jetport and Congress Street. This 

site was underlain by about 12.2 m (40 feet) of weak 

marine clay. Test results indicated that the clay is an 

overconsolidated, moderately sensitive, inorganic 

clay of low plasticity. Undrained shear strength varied 

from approximately 72 kiloPascals (kPa) (1,500 pounds 

per square foot [psf]) near the top to 19 kPa (400 psf) 

near the center of the layer.

The designers for the project (the Maine offices 

of HNTB, Inc., and Haley and Aldrich, Inc., and the 

University of Maine) found that embankments 

built of conventional soil were too heavy, resulting 

in an unacceptably low factor of safety against 

slope instability. They looked at several ways to 

strengthen the foundation soils, but these methods 

were too costly. Construction of the embankments 

using lightweight fill was chosen as the lowest 

cost alternative. They considered several types of 

lightweight fill, including TDA, expanded polystyrene 

insulation boards, and expanded shale. TDA was 

chosen because it was $300,000 cheaper than the 

other alternatives. Moreover, the project would put 

some 1.2 million tires to a beneficial end use. Wick 

drains were also used to accelerate consolidation of 

the foundation soils.

Project Layout and Construction

Several steps were taken to comply with the 

guidelines to limit heating of thick TDA fills (Refs. 1, 

2). The guidelines required that a single TDA layer 

be no thicker than 3 m (10 feet). Therefore, the 

TDA layer was broken up into two layers, each up 

to 3 m (10 feet) thick, separated by 0.9 m (3 feet) 

of soil, as shown in Exhibit E-1. Low-permeability 

soil with a minimum of 30 percent passing the 

No. 200 sieve was placed on the outside and top 

of the fill to limit inflow of air and water. The 

final precaution to limit heating was to use large 

Type B TDA with a minimum of fines. The TDA 

had less than 50 percent by weight passing the 

75-mm (3-inches) sieve, 25 percent passing the 

38-mm (11⁄2-inches) sieve, and less than 1 percent 

passing the No. 4 sieve. The TDA had a maximum 

size measured in any direction of 300 mm (12 

inches) to ensure that it could be easily placed 

with conventional construction equipment. The 

embankment was topped with 0.61 m (2 feet) of 

Exhibit E-1. Cross section through embankment constructed on soft marine clay for the Portland Jetport Interchange (Ref. 5)
A-14

Appendix E Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

low-permeability soil, 1.22 m (4 feet) of granular 

soil, plus 1.22 m (4 feet) of temporary surcharge. 

The purpose of the surcharge was to increase the 

rate of consolidation of the soft clay foundation 

soils and was unrelated to the TDA fill.

The TDA was placed with conventional 

construction techniques. First, geotextile was 

placed on the prepared base to act as a separator 

between the TDA and surrounding soil. Then, the 

TDA was spread in 300-mm (12-inch)-thick lifts 

using a Caterpillar D-4 dozer, as shown in Exhibit 

E-2. Each lift was compacted with six passes of 

a vibratory roller with a minimum 9.8-metric ton 

(10-ton) operating weight. After the TDA was in 

place, the contractor placed a geotextile separator 

on the sides and top of the TDA zone. The 

surrounding soil cover was placed as the TDA was 

placed.

Construction Settlement and In-place 

Unit Weight

Settlement plates were installed at the top and 

bottom of each TDA layer to monitor settlement. 

Compression of each TDA layer at the end of 

fill placement is summarized in Table E-1. The 

compression predicted based on laboratory 

compression tests on 75-mm (3-inches) maximum 

size TDA is also shown. It is seen that the predicted 

compression is significantly greater than the 

measured value. Thus, the compressibility of TDA 

with a 300-mm (12-inches) maximum size appears 

to be less than for 75-mm (3-inches) maximum size 

TDA. This compression was one factor that led to 

overpredicting the final in-place unit weight. The final 

in-place unit weight was predicted to be 0.93 Mg/m3 

(58 pcf) compared with an actual value of 0.79 Mg/

m3 (49 pcf), a difference of 18 percent. This difference 

cannot be entirely accounted for by the difference 

in compressibility. Thus, it is likely that the initial 

(uncompressed) unit weight of the larger TDA is less 

than for 75-mm (3-inches) maximum size TDA.

Temperature Measurements

Monitoring the temperatures of the TDA fill was of 

great interest because of past problems with heating 

of thick TDA fills (Ref. 4). The warmest temperatures 

were measured at the time of placement when the 

black TDA was heated by exposure to direct sunlight. 

Initial temperatures ranged from 24 to 38°C (75 to 

100°F). After it was covered with the first few lifts 

of fill, the temperatures began dropping with time. 

Temperatures were still dropping when monitoring 

was discontinued in April 1998. Typical temperature 

measurements are shown on Exhibit E-3. From these 

results, it can be seen that there was no evidence of 

self-heating.

Case History – North Abutment 

Approach Fill

The key element of the Topsham Brunswick Bypass 

Project was the 300-m (984-feet) long Merrymeeting 

Bridge over the Androscoggin River. The subsurface 

profile at the location of the north abutment 

consisted of 3 to 6 m (10 to 20 feet) of marine silty 

sand overlying 14 to 15 m (45 to 50 feet) of marine 

silty clay. The clay is underlain by glacial till and 

then bedrock. The existing riverbank had a factor of 

safety against a deep-seated slope failure that was 

near 1. Moreover, the design called for an approach 

fill leading up to the bridge abutment that would 

Exhibit E-2. Caterpillar D-4 spreading TDA for lightweight embankment 

fill at Portland Jetport Interchange 

Table E-1.Measured compressibility of TDA layer for Portland Jetport Interchange project.

Settlement

Plate No. Location Lower TDA layer Upper TDA layer

Measured Predicted Measured Predicted

SW1 25+00,C/L 12.6% 22% 8.3% 14%

SW4 26+00, C/L 13.4% 21% 11.2% 14%

SE1 30+00, C/L 19.1% 22% 10.9% 14%

SE4 31+00, C/L 17.3% 23% 9.3% 14%

Avg. C/L Plates 15.6% 22% 9.9% 14%
A-15

Appendix E Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

have further lowered the factor of safety. Thus, it 

was necessary to both improve the existing factor of 

safety and allow construction of the approach fill. The 

best solution was to excavate some of the existing 

riverbank and replace it with a 4.3-m (14-foot)-

thick layer of TDA. TDA had the added advantage 

of reducing lateral pressures against the abutment 

wall. Other types of lightweight fill were considered, 

including geofoam and expanded shale aggregate. 

However, TDA proved to be the lowest-cost solution. 

The project used some 400,000 scrap tires (Ref. 9).

Project Layout and Construction

The surficial marine sand was excavated to elevation 

5.2 m (17 feet) and then the abutment wall supported 

by an H-pile was constructed. A 4.3-m (14 foot)-

thick zone of TDA was placed from station 53+50.6 

m (175+50 feet) to the face of the abutment wall at 

station 53+72.0 m (176+20 feet). The fill tapers from 

a thickness of 4.3 m (14 feet) at station 53+50.6 m 

(175+50 feet) to zero thickness at station 53+35.4 

m (175+00 feet) to provide a gradual transition 

between the TDA layer and the conventional 

fill. It was estimated that the TDA layer would 

compress 460 mm (18 inches) from the weight 

of the overlying soil layers. As a result, the layer 

was built up an additional 460 mm (18 inches) 

so that the final compressed thickness would be 

4.3 m (14 feet). The TDA layer was enclosed in a 

woven geotextile (Niolon Mirafi 500X) to prevent 

infiltration of surrounding soil. The TDA was spread 

with front-end loaders and bulldozers and then 

compacted by six passes of a smooth drum vibratory 

roller (Bomag BW201AD) with a static weight of 9,432 

kg (10.4 tons). The thickness of a compacted lift was 

limited to 305 mm (12 inches). It was determined 

that approximately 15 inches (381 mm) of loose TDA 

needed to be initially placed to obtain a compacted 

thickness of 305 mm (12 inches). TDA placement 

began on September 25, 1996, and was completed 

on October 3, 1996. A longitudinal section of the 

Exhibit E-3. Temperatures in lower tire shed layer of lightweight embankment fill at Portland Jetport Interchange 

6/30/97 9/28/97 12/27/97 3/27/98 6/25/98

50

55

60

65

70

75

80

85

90

95

100

T

e

m

p

era

t

ure (D

e

g. F)

Embankment 2

Lower Tire Shred Layer

TH23

TH25

TH27

TH33
A-16

Appendix E Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

completed abutment and embankment is shown 

in Exhibit E-4.

This project was designed and built before the 

guidelines were developed to limit self-heating 

of TDA fills. However, the project included design 

features to limit self-heating. The first was to use 

larger Type B TDA in the lower portion of the fill 

from elevation 5.2 m (17 feet) to elevation 8.2 m 

(27 feet). The Type B TDA was specified to have a 

maximum dimension measured in any direction 

of 305 mm (12 inches); a minimum of 75 percent 

(by weight) passing the 203-mm (8-inches) square 

mesh sieve, a maximum of 25 percent (by weight) 

passing the 38-mm (11⁄2-inches) square mesh sieve, 

and a maximum of 5 percent (by weight) passing 

the No. 4 (4.75-mm) sieve. No requirement for the 

percent passing the 3-inches (75-mm) sieve was 

included for this project. Gradation tests showed 

that the TDA generally had a maximum dimension 

smaller than 150 mm (6 inches). Type A TDA, with a 

maximum size of 75 mm (3 inches), were placed from 

elevation 8.2 m (27 feet) to the top of the TDA fill. It 

would have been preferable to use the larger Type B 

TDA for the entire thickness. However, a significant 

quantity of Type A TDA had already been stockpiled 

near the project prior to the decision to use larger 

TDA. It was judged that it would be acceptable to use 

the smaller Type A TDA in the upper portion of the 

fill. Moreover, it would have been preferable to limit 

the total thickness of the TDA layer to 3 m (10 feet), as 

recommended by the guidelines to limit self-heating.

As an additional step to reduce the possibility of selfheating, the TDA are overlain by a layer of compacted 

clayey soil with a minimum of 30 percent passing the 

No. 200 (0.075 mm) sieve. The purpose of the clay 

layer is to minimize the flow of water and air though 

the TDA. The clay layer is approximately 0.61 m (2 

feet) thick and is built up in the center to promote 

drainage toward the side slopes. A 0.61-m (2-foot)-

thick layer of common borrow was placed over the 

clay layer. Overlying the common borrow is 0.76 m 

(2.5 feet) of aggregate subbase.

TDA undergoes a small amount of time-dependent 

settlement. For this project, a thick TDA fill adjoined a 

pile-supported bridge abutment, leading to concerns 

that there could be differential settlement at the 

junction with the abutment. However, Tweedie 

and others (Ref. 6) showed that most of the timedependent settlement occurs within the first 60 days. 

To accommodate the time-dependent settlement 

before paving, the contractor was required to place 

an additional 0.3 m (1 foot) of subbase aggregate 

as a surcharge to be left in place for a minimum of 

60 days. In fact, the overall construction schedule 

allowed the contractor to leave the surcharge in 

place from October 1996 through October 1997. 

The surcharge was removed in October 1997 and 

the roadway was topped with 229 mm (9 inches) of 

bituminous pavement. The highway was opened to 

traffic on November 11, 1997. Additional construction 

information is given in Cosgrove and Humphrey (Ref. 

3).

Exhibit E-4. Longitudinal section through North Abutment TDA fill 

el. 9.4 m

Clay

el. 5.2 m

el. 8.2 m

Type B 

Tire Shreds

Native

Soil

Type A

Tire Shreds

229 mm Bituminous

Concrete Pavement

Aggregate

Subbase

el. 11.3 m

el. 10.1 m

el. 10.7 m

Station 

53+35.4

Common

Borrow Granular

Borrow

Aggregate

Subbase

Geotextile

Piles

Station

53+72.0

@ Center Line

Station

53+50.6

Concrete 

Approach Slab
A-17

Appendix E Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

Instrumentation

Four types of instruments were installed: pressure 

cells cast into the back face of the abutment wall; 

and vibrating wire settlement gauges, settlement 

plates, and temperature sensors placed in the TDA fill. 

Vibrating wire pressure cells were installed to monitor 

lateral earth pressure against the abutment wall. 

Three Roctest model TPC pressure cells (PC1-1, PC1-2, 

and PC1-3) were installed on the face of the abutment 

wall 4 m (13 feet) right of centerline, and three Roctest 

model EPC pressure cells (PC2-1, PC2-2, and PC2-3) 

were installed 4 m (13 feet) left of centerline, as shown 

in Exhibit E-5. TDA was placed against all the cells.

Measured Horizontal Pressure and 

Settlement

The lateral pressure at the completion of TDA 

placement (October 3, 1996), completion of soil 

cover, and placement of surcharge (October 9, 1996) 

is summarized in Table E-2. Lateral pressures on 

October 31, 1996, are also shown. It is seen that the 

pressures increased with depth at completion of TDA 

placement. However, at completion of soil cover 

and surcharge placement, the pressures recorded by 

cells PC1-1, PC1-2, and PC1-3 were nearly constant 

with depth and ranged between 17.05 and 19.61 kPa 

(356 and 410 psf). These findings are consistent with 

at-rest conditions measured on an earlier project 

(Tweedie and others 1997; 1998a). Cells PC2-1, 

PC2-2, and PC2-3 showed different behavior. At 

completion of TDA placement 9, 1996, cell PC2-2 

showed a pressure of 30.22 kPa (631psf), while 

cell PC2-1, located only 1.07 m (3.5 feet) lower, 

was 20.04 kPa (418 psf) and cell PC2-3, located 

1.07 m (3.5 feet) above PC2-2, was 12.31 kPa (257 

psf). These cells were the less stiff EPC cells. Large 

scatter has been observed with EPC cells on an 

earlier TDA project (Refs. 6, 7, 8). This scatter is 

thought to be caused, at least in part, when the 

large TDA creates a non-uniform stress distribution 

on the face of the pressure cell. The average 

pressure recorded by the three PC2 cells was 20.85 

kPa (435 psf), which is slightly higher than the PC1 

cells. Between October 9, 1996 and October 31, 

1996, the lateral pressure increased by 1 to 2 kPa (20 

to 40 psf). The pressures have been approximately 

constant since that time.

The TDA fill compressed about 370 mm (14.6 inches) 

during placement of the overlying soil cover. In the 

next 60 days, the fill settled an additional 135 mm (5.3 

inches). Between December 15, 1996, and December 

31, 1997, the fill underwent an additional 15 mm (0.6 

inches) of time-dependent settlement. The rate of 

settlement had decreased to a negligible level by late 

1997. The total compression of the TDA fill was 520 

mm (20.4 inches) which was 13 percent greater than 

Exhibit E-5. Location of pressure cells in North Abutment (Ref. 3)
A-18

Appendix E Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

the 460 mm (18 inches) that was anticipated based 

on laboratory compression tests. The difference 

is the result, at least in part, of time-dependent 

settlement that is not accommodated in the shortterm laboratory tests. The final compressed density 

of the TDA was about 0.9 Mg/m3 (57 pcf), higher 

than for the Portland Jetport Project, most likely 

because of the smaller size of the TDA used for this 

project.

Temperature of TDA Layer

A small amount of self-heating of the TDA 

occurred. Five out of the 12 thermistors in the 

Type A TDA experienced a peak temperature of 

between 30 and 40°C (86 and 104°F). In contrast, 

only two of the 18 thermistors in the larger Type B 

TDA experienced a peak in this range, and these 

two sensors may have been influenced by warmer 

overlying Type A TDA. This difference suggests 

that larger TDA is less susceptible to heating. In 

any case, the peak temperatures were too low 

to be of concern. Since early 1997, the overall 

trend has been one of decreasing temperature. 

However, the temperature of the TDA appears to 

be slightly influenced by seasonal temperature 

changes.

References

1. Ad Hoc Civil Engineering Committee. 1997. 

“Design Guidelines to Minimize Internal Heating 

of Tire Shred Fills.” Scrap Tire Management 

Council, Washington, DC. 4 pp.

2. ASTM International. 1998. “Standard Practice 

for Use of Scrap Tires in Civil Engineering 

Applications.” ASTM D6270-98, ASTM 

International. W. Conshohocken, Pennsylvania.

3. Cosgrove, T.A., and Humphrey, D.N. 1999. “Field 

Performance of Two Tire Shred Fills in Topsham, 

Maine.” A report for the Maine Department of 

Transportation by Department. of Civil and 

Environmental Engineering, University of Maine, 

Orono, Maine.

4. Humphrey, D.N. 1996. “Investigation of 

Exothermic Reaction in Tire Shred Fill Located on 

SR 100 in Ilwaco, Washington.” Prepared for the 

Federal Highways Administration, Washington, 

D.C. 60 pp.

5. Humphrey, D.N., Whetten, N., Weaver, J., Recker, 

K., and Cosgrove, T.A. 1998. “Tire TDA as 

Lightweight Fill for Embankments and Retaining 

Walls.” Proceedings of the Conference on 

Recycled Materials in Geotechnical Applications, 

C. Vipulanandan and D. Elton, eds., ASCE, pp. 51-

65.

6. Tweedie, J.J., Humphrey, D.N. and Sandford, 

T.C. 1997. “Tire Chips as Lightweight Backfill for 

Retaining Walls - Phase II,” A Study for the New 

England Transportation Consortium, Department 

of Civil and Environmental Engineering, 

University of Maine, Orono, Maine, 291pp.

7. Tweedie, J.J., Humphrey, D.N., and Sandford, 

T.C. 1998a. “Full Scale Field Trials of Tire TDA 

as Lightweight Retaining Wall Backfill, At-Rest 

Conditions.” Transportation Research Record No. 

1619. TRB, Washington, D.C. pp. 64-71.

8. Tweedie, J.J., Humphrey, D.N., and Sandford, 

T.C. 1998b. “Tire TDA as Retaining Wall Backfill, 

Active Conditions.” Journal of Geotechnical and 

Geoenvironmental Engineering. ASCE, Vol. 124, 

No. 11. pp. 1061-1070.

9. Whetten, N., Weaver, J. Humphrey, D., and 

Sandford, T. 1997. “Rubber Meets the Road 

in Maine.” Civil Engineering, Vol. 67, No. 9. 

September. pp. 60-63.

Table E-2. Summary of Lateral Pressures on Abutment Wall.

Date

PC1-1 PC2-1 PC1-2 PC2-2 PC1-3 PC2-3

Cell elev. = 6.70 m Cell elev. = 7.77m Cell elev. = 8.84 m

10/3/962 7.841 7.41 6.04 7.27 2.62 1.41

10/9/963 17.04 20.04 19.61 30.22 17.05 10.91

10/31/96 18.27 21.05 20.98 32.84 20.24 12.31

1

Horizontal pressure in kPa.

2

Date TDA placement completed.

3

Date soil cover and surcharge placement completed.
A-19

Appendix F Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

APPENDIX F

Comparative Transportation 

Cost Example

Vehicle Type

Pickup Truck Pickup with Trailer

Basis Cost/mile Basis Cost/mile

Labor ($/hr) $10/hour, 30 miles/hour $0.33 $10/hour, 30 miles/hour $0.33

Fuel ($/mile) $4.00/gallon, 15 miles/

gallon $0.27 $4.00/gallon, 12 miles/gallon $0.33

Maintenance($/mile) $1000/yr, 30,000 miles/yr $0.03 $2000/yr, 30,000 miles/yr $0.07

Subtotal-Variable Cost $0.63 $0.73

Insurance $1000/yr, 30,000 miles/yr $0.03 $1000/yr, 30,000 miles/yr $0.03

Depreciation $2500/yr, 30,000 miles/yr $0.08 $2500/yr, 30,000 miles/yr $0.08

ROI $15,000x20%= $3,000/yr $0.10 $18000x20%= $3600/yr $0.12

Subtotal-Fixed Cost $0.22 $0.24

Total costs $0.85 $0.97

Tires/load 50 250

Cost/mile/tire

for 1 mile $0.02 for 1 mile $0.004

for 25 miles $0.43 for 25 miles $0.10

for 100 miles $1.70 for 100 miles $0.39

for 200 miles $3.40 for 200 miles $0.78

for 500 miles $8.50 for 500 miles $1.94

Box Truck Tractor with 48 foot trailer

Basis Cost/mile Basis Cost/mile

Labor ($/hr) $12/hour, 30 miles/hour $0.40 $15/hour, 30 miles/hour $0.50

Fuel ($/mile) $4.00/gallon, 8 miles/

gallon $0.50 $4.00/gallon, 6 miles/gallon $0.67

Maintenance($/mile) $2500/yr, 30,000 miles/yr $0.08 $3500/yr, 30,000 miles/yr $0.12

Subtotal-Variable Cost $0.98 $1.28

Insurance $2000/yr, 30,000 miles/yr $0.07 $3000/yr, 30,000 miles/yr $0.07

Depreciation $3500/yr, 30,000 miles/yr $0.12 $10000/yr, 30,000 miles/yr $0.33

ROI $25000x20%= $5000/yr $0.17 $80000x20%= $16000/yr $0.53

Subtotal-Fixed Cost $0.35 $0.93

Total costs $1.33 $2.22

Tires/load 400 1,400

Cost/mile/tire

for 1 mile $0.003 for 1 mile $0.002

for 25 miles $0.08 for 25 miles $0.04

for 100 miles $0.33 for 100 miles $0.16

for 200 miles $0.67 for 200 miles $0.32

for 500 miles $1.67 for 500 miles $0.79
A-20

Appendix G Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

APPENDIX G

Scrap Tire Processing Facility 

Economic Parameters

BASIS

The projected operating mode is a single facility capable of receiving and processing 250,000 to 1,000,000 

passenger tire equivalents (PTEs)/year into specific shredded product sizes ranging from Class B tire-derived 

aggregate (TDA) to 1-inch nominal chips

SITE PARAMETERS

Property Size:

Approximately 5 acres of flat, dry land in a central location with highway access and stable soil, plus additional 

property for product storage if more than 1 month’s inventory is required. 

Property Use: 

3 acres for site operations, equipment movement and limited tire storage

2 acres for office and maintenance trailers and limited product storage, as well as water storage if applicable

Common Property Improvements:

Fenced and gated perimeter provides access control to decrease theft, vandalism, and arson

Operating area lighting, and possibly storage area lighting (depending on surroundings), enhances 

operating flexibility, safety, and security

Soil stabilization of storage and working areas: (1) decreases tire contamination and associated equipment 

maintenance, and (2) decreases product contamination for greater marketability and value

Concrete over about 1 acre of the centralized operating area prevents water displaced from tires during 

handling and processing; creating wet and undesirable conditions. A berm (3 to 4 feet high) around the 

perimeter of the storage area controls dispersion of pyrolytic oil or water if there is a fire.

Water accessibility or a water storage pond (lined if necessary) for emergency fire fighting

Electrical power for processing equipment, including a transformer if the available power is not stepped down

Office and associated equipment required to conduct business

Shop area and tools required to maintain equipment

Basic operation can be conducted outside, but efficiency may be impaired by weather. A portable cover may 

be desirable for shredder maintenance.

Additional Product Storage Requirements:

Depending on the products and markets, seasonal markets may require inventory up to 80 percent of annual 

production in an environmentally safe manner that minimizes the probability of a fire and maximizes the ability 

to control a fire if one occurs. Such an inventory would require an additional:

5 acres for 10 piles 50 x 150 x 10 feet (with 50 feet clear around each one) for storage of 800,000 PTEs of TDA

About 760 meters (2,500 linear feet) of fencing to enclose this area
A-21

Appendix G Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

EQUIPMENT FOR TYPE B TDA

Processing - If the sole product is Type B TDA, one of the least expensive single machines to purchase and 

maintain is the Barclay 4.9-inch horizontal primary shredder mounted at a 45-degree angle with a classification 

and recycle system. Alternatives include tire shredders with 4-inch knife spacing, but these generally have 

higher capital and operating costs. The major components and approximate current costs in $US are as follows:

Shredder with extended infeed conveyor $230,000

Classifier $45,000

Recycle conveyors (local supply) $36,000

Discharge conveyor (local supply) $50,000

Transportation (estimated from California) $5,000

Equipment Subtotal $366,000

Installation (approximate) $75,000

Spare parts $40,000

Miscellaneous and contingency $100,000

Total processing equipment $581,000

Additional Equipment – Required for movement of tires and shreds

Front end loader (used) $60,000

Supplemental Bobcat $20,000

Electrical supply/controls (estimate) $25,000

Dump truck/trailer for on-site shred movement $20,000

Total additional equipment $125,000

FOR NOMINAL 2 INCH SHREDS (3-4 INCH MAX SIZE)

Processing - Normal use is a single high-capacity tire shredder with a classification and recycle system for 

volumes up to 1 million tires/year. The major components and approximate current costs in $US are as 

follows:

Shredder $350,000 - $500,000

Infeed conveyor/mechanical system $ 25,000 - $150,000

Classifier $ 45,000 - $230,000

Recycle conveyors (local supply) $ 36,000

Discharge conveyor (local supply) $ 50,000

Transportation (estimated) $ 12,000 - $ 20,000

Equipment Subtotal $518,000 - $986,000

Installation (approximate) $100,000

Spare parts $ 60,000

Miscellaneous and contingency $125,000

Total processing equipment $803,000 -$1,271,000
A-22

Appendix G Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

Additional Equipment – Required for movement of tires and shreds

Front end loader (used) $60,000

Supplemental Bobcat $20,000

Electrical supply/controls (estimate) $ 25,000

Dump truck/trailer for on-site shred movement $ 20,000

Total additional equipment $125,000

FOR NOMINAL 1 INCH SHREDS

Processing – Processing capital costs will be the same as for 2-inch shreds, but magnets may be required 

to remove chips that contain bead wire for some applications. If there is no market or reasonable disposal 

alternative for this material (30 to 40 percent), then additional equipment can be installed to liberate the wire 

for sale (as previously discussed) and salvage the rubber in a variety of sizes down to crumb rubber. The major 

components and approximate current costs in $US are as follows:

Total 2-inch equipment $803,000 - $1,271,000

Additional magnets/conveyors $ 60,000 -$ 110,000

Total processing equipment $863,000 -$1,381,000

Additional cost for wire liberation/recovery/

Classification equipment to produce saleable

wire and some crumb rubber products $500,000 -$1,200,000

OPERATING COST COMPONENTS

Typical Staffing level for one shift/5 day operation (some jobs can be combined in low-volume operations)

1 Manager

1 Office/accounting

1 Shipment receiving/monitoring

1 Supervisor/maintenance manager

1 Loader operator

1-2 Laborer/maintenance

Professional Services (such as accounting, marketing, and legal)

Processing/Maintenance

For Class B TDA

Processing equipment maintenance $ 6.00/ton

Loader/Bobcat maintenance $ 2.00/ton

Power for Equipment 

For 1.0 million tires/year

(150 hp x 70% load x .746 kilowatt [kW] conversion = 78 kW/hour x 2,080 hours/yr = 162,240 kW/year) 

For 0.5 million tires/year, est 50 % load factor or 115,000 kW/year

For 0.25 million tires/year, est 40 % load or 92,000 kW/yr

For 2-inch nominal shreds

Processing equipment maintenance $15.00/ton

Loader/Bobcat maintenance $ 2.00/ton

Power for Equipment 

For 1.0 million tires/year
A-23

Appendix G Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

(250 hp x 70% load x .746 kW conversion = 131 kW/hour x 2,080 hours/yr = 272,480 kW/year) 

For 0.5 million tires/year, est 50% load factor or 195,000 kW/year

For 0.25 million tires/year, est 40% load or 156,000 kW/yr

For 1-inch nominal shreds

Processing equipment maintenance $25.00/ton

Loader/Bobcat maintenance $ 2.00/ton

Power for Equipment 

For 1.0 million tires/year

(250 hp x 85%load x .746 kW conversion = 159 kW/hour x 2,080 hours/yr = 330,000 kW/year) 

For 0.5 million tires/year, est 70% load factor or 272,000 kW/year

For 0.25 million tires/year, est 55% load or 213,000 kW/yr

OTHER FIXED COST COMPONENTS

Insurance

Financing

Government Taxes
A-24

Appendix H Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

APPENDIX H

Comparative Volume Sensitivity 

of Tire Processing Facilities

TIRE-DERIVED AGGREGATE (TDA) PRODUCT

VARIABLE COSTS

COST 

COMPONENT

PROCESSING RATE (Tires/year)

250,000 500,000 1,000,000 

Number Cost/year Cost/tire Number Cost/year Cost/tire Number Cost/year Cost/tire

Labor

Supervisor 1 $40,000 $0.16 1 $40,000 $0.08 1 $40,000 $0.04 

Manual 2 $48,000 $0.19 2 $48,000 $0.10 3 $72,000 $0.07 

Subtotal 3 $88,000 $0.35 3 $88,000 $0.18 4 $112,000 $0.11 

Power (mw/yr) @ 

$100/mw 92 $9,200 $0.04 115 $11,500 $0.02 162 $16,200 $0.02

Maintenance

Shredder

($/ton) 6 $15,000 $0.06 6 $30,000 $0.06 6 $60,000 $0.06 

Other

($/ton) 2 $5,000 $0.02 2 $10,000 $0.02 2 $20,000 $0.02 

Subtotal 8 $20,000 $0.08 8 $40,000 $0.08 8 $80,000 $0.08 

Wire Disposal

(tons) 0 - - 0 - - 0 - - 

TOTAL VARIABLE 

COST $117,200 $0.47 $139,500 $0.28 $208,200 $0.21 

Depreciation (real with tire processing equipment – typically 5 – 8 years)

FIXED COSTS

COST 

COMPONENT

PROCESSING RATE (Tires/year)

250,000 500,000 1,000,000

Number Cost/year Cost/tire Number Cost/year Cost/tire Number Cost/year Cost/tire

Administration

Manager 1 $50,000 $0.20 1 $50,000 $0.10 1 $50,000 $0.05 

Sales/service By Mgr - - By Mgr - - 1 $40,000 $0.04 

Clerical 1 $20,000 $0.08 1 $20,000 $0.04 1 $20,000 $0.02 

Office expense $18,000 $0.07 $18,000 $0.04 $18,000 $0.02 

Prof. Services $5,000 $0.02 $10,000 $0.02 $10,000 $0.01 

Subtotal $93,000 $0.37 $98,000.00 $0.20 $138,000.00 $0.14 

Capital charges

Amortization 

(12.5%/year)

$97,813 $0.39 $97,813 $0.20 $97,813 $0.10 

General Expense

Insurance (1% of 

$1M)

 $10,000 $0.04 $10,000 $0.02 $10,000 $0.01 

Prop Tax (1% of 

$1M)

 $10,000 $0.04 $10,000 $0.02 $10,000 $0.01 

Subtotal $20,000 $0.08 $20,000 $0.04 $20,000 $0.02 

TOTAL FIXED 

COSTS

 $210,813 $0.84 $215,813 $0.43 $255,813 $0.26 

TOTAL COST $328,013 $1.31 $355,313 $0.71 $464,013 $0.46 

PROFIT (25% 

ROC on $1M)

 $250,000 $1.00 $250,000 $0.50 $250,000 $0.25 

TOTAL PRICE $578,013 $2.31 $605,313 $1.21 $714,013 $0.71 
A-25

Appendix H Scrap Tires:

Management for the U.S. and MexicoHandbook on Recycling Applications and

COMPARATIVE VOLUME SENSITIVITY OF TIRE PROCESSING FACILITIES

NOMINAL 2-INCH SHREDS

VARIABLE COSTS

COST 

COMPONENT

PROCESSING RATE (Tires/year)

250,000 500,000 1,000,000 

Number Cost/year Cost/tire Number Cost/year Cost/tire Number Cost/year Cost/tire

Labor

Supervisor 1 $40,000 $0.16 1 $40,000 $0.08 1 $40,000 $0.04 

 Manual 2 $48,000 $0.19 2 $48,000 $0.10 3 $72,000 $0.07 

 Subtotal 3 $88,000 $0.35 3 $88,000 $0.18 4 $112,000 $0.11 

Power (mw/yr) @ 

$100/mw 156 $15,600 $0.06 195 $19,500 $0.04 272 $27,200 $0.03 

Maintenance

 Shredder($/ton) 15 $37,500 $0.15 15 $75,000 $0.15 15 $150,000 $0.15 

 Other($/ton) 2 $5,000 $0.02 2 $10,000 $0.02 2 $20,000 $0.02 

 Subtotal 17 $42,500 $0.17 17 $85,000 $0.17 17 $170,000 $0.17 

Wire 

Disposal(tons) 0 - - 0 - - 0 - - 

TOTAL VARIABLE 

COST $146,100 $0.58 $192,500 $0.39 $309,200 $0.31 

FIXED COSTS

COST 

COMPONENT

PROCESSING RATE (Tires/year)

250,000 500,000 1,000,000 

Number Cost/year Cost/tire Number Cost/year Cost/tire Number Cost/year Cost/tire

Administration

 Manager 1 $50,000 $0.20 1 $50,000 $0.10 1 $50,000 $0.05 

 Sales/service By Mgr - - By Mgr - - 1 $40,000 $0.04 

 Clerical 1 $20,000 $0.08 1 $20,000 $0.04 1 $20,000 $0.02 

 Office expense $18,000 $0.07 $18,000 $0.04 $18,000 $0.02 

 Prof. Services $5,000 $0.02 $10,000 $0.02 $10,000 $0.01 

 Subtotal $93,000 $0.37 $98,000 $0.20 $138,000 $0.14 

Capital charges

Amortization 

(12.5%/year)

$150,000 $0.60 $150,000 $0.30 $150,000 $0.15 

General Expense

Insurance (1% of 

$1.5M)

 $15,000 $0.06 $15,000 $0.03 $15,000 $0.02 

Prop Tax (1% of 

$1.5M)

 $15,000 $0.06 $ 15,000 $0.03 $15,000 $0.02 

Subtotal $30,000 $0.12 $30,000 $0.06 $30,000 $0.03 

TOTAL FIXED 

COSTS

 $273,000 $1.09 $278,000 $0.56 $318,000 $0.32 

TOTAL COST $288,000 $1.15 $293,000 $0.59 $333,000 $0.33 

PROFIT (25% 

ROC on $1.5M)

 $375,000 $1.50 $375,000 $0.75 $375,000 $0.38 

TOTAL PRICE 

REQUIRED

 $663,000 $2.65 $668,000 $1.34 $708,000 $0.71
A-26

Appendix H Scrap Tires: Handbook on Recycling Applications and

Management for the U.S. and Mexico

COMPARATIVE VOLUME SENSITIVITY OF TIRE PROCESSING FACILITIES

NOMINAL 1-INCH SHREDS

VARIABLE COSTS

COST 

COMPONENT

PROCESSING RATE (Tires/year)

250,000 500,000 1,000,000 

Number Cost/year Cost/tire Number Cost/year Cost/tire Number Cost/year Cost/tire

Labor

Supervisor 1 $40,000 $0.16 1 $40,000 $0.08 1 $40,000 $0.04 

Manual 2 $48,000 $0.19 2 $48,000 $0.10 3 $72,000 $0.07 

Subtotal 3 $88,000 $0.35 3 $88,000 $0.18 4 $112,000 $0.11 

Power (mw/yr) @ 

$100/mw

213 $21,300 $0.09 272 $27,200 $0.05 330 $33,000 $0.03 

Maintenance 

 Shredder($/ton) 25 $62,500 $ 0.25 25 $125,000 $0.25 25 $250,000 $0.25 

 Other($/ton) 2 $5,000 $0.02 2 $10,000 $0.02 2 $20,000 $0.02 

 Subtotal 27 $67,500 $0.27 27 $135,000 $0.27 27 $270,000 $0.27 

Wire 

Disposal(tons)

50 $1,500 $0.01 100 $3,000 $0.01 200 $6,000 $0.01 

TOTAL VARIABLE 

COST

$178,300 $0.71 $253,200 $0.51 $421,000 $0.42

FIXED COSTS

COST 

COMPONENT

PROCESSING RATE (Tires/year)

250,000 500,000 1,000,000 

Number Cost/year Cost/tire Number Cost/year Cost/tire Number Cost/year Cost/tire

Administration

 Manager 1 $50,000 $0.20 1 $50,000 $0.10 1 $50,000 $0.05 

 Sales/service By Mgr - - By Mgr - 1 $40,000 $0.04 

 Clerical 1 $20,000 $0.08 1 $20,000 $0.04 1 $20,000 $0.02 

 Office expense $18,000 $0.07 $18,000 $0.04 $18,000 $0.02 

 Prof. Services $5,000 $0.02 $10,000 $0.02 $10,000 $0.01 

 Subtotal $93,000 $0.37 $98,000 $0.20 $138,000 $0.14 

Capital charges

Amortization 

(12.5%/year) $162,500 $0.65 $162,500 $0.33 $162,500 $0.16 

General Expense

 Insurance (1% 

of $1.6M) $16,000 $0.06 $16,000 $0.03 $16,000 $0.02 

Prop Tax (1% of 

$1.6M) $16,000 $0.06 $16,000 $0.03 $16,000 $0.02 

Subtotal $ 32,000 $0.13 $32,000 $0.06 $32,000 $0.03 

TOTAL FIXED 

COSTS $287,500 $1.15 $292,500 $0.59 $332,500 $0.33 

TOTAL COST $303,500 $1.21 $308,500 $0.62 $348,500 $0.35 

PROFIT (25% 

ROC on $1.6M) $400,000 $1.60 $400,000 $0.80 $400,000 $0.40 

TOTAL PRICE $703,500 $2.81 $708,500 $1.42 $748,500 $0.75