Using Recycled Industrial 

Materials in Roadways

Greening the Nation’s Infrastructure. This 

fact sheet discusses the use of industrial materials in roadways and other 

infrastructure projects as an alternative to virgin materials and construction 

products. Industrial materials are the byproducts of industrial processes. 

Each year in the United States, industries produce over half a billion tons 

of potentially usable materials, such as coal combustion products (CCPs), 

construction and demolition (C&D) materials, spent foundry sands, used 

tires, and slags. Many have chemical and physical properties that make them 

valuable resources when recycled or beneficially reused, but they are often 

disposed of as waste. The U.S. Environmental Protection Agency (EPA) is 

committed to increasing the recycling of industrial materials as part of its 

Resource Conservation Challenge, a national effort to save energy and reduce 

greenhouse gas emissions by managing materials more efficiently. Industrial 

materials recycling is helping to green the nation’s infrastructure by making 

roadways more durable, conserving natural resources, decreasing energy use, 

and reducing greenhouse gas emissions.

www.epa.gov/industrialmaterials
An Overview:

Roadway Applications for 

Industrial Materials

Roadways are a central component of the nation’s 

infrastructure and present a wide array of opportunities for 

using industrial materials. This diagram illustrates the most 

common roadway applications for industrial materials. Note 

that the availability of specific industrial materials can vary 

regionally, so visit the Web sites in the "Resources for More 

Information" section of this document for information on 

identifying suppliers of industrial materials in your region as 

well as local C&D materials recyclers.

Recycling Industrial Materials in Concrete Pavements. 

This image portrays the use of industrial materials in hot-mix asphalt 

pavement (HMA); however, industrial materials have very similar 

applications in traditional portland cement concrete 

pavement (PCC). Both HMA and PCC pavements 

require aggregates, and the list of aggregates 

under the “Concrete Retaining Wall” and 

“Asphalt Base” applications can be used 

in both HMA and PCC roads. PCC roads 

can incorporate ground granulated blast 

furnace slag and reclaimed concrete 

aggregate (RCA) more easily and in 

larger volumes than HMA can. See the 

American Association of State Highway 

and Transportation Officials (AASHTO) 

provisional standard MP 16-07 for use of 

RCA in hydraulic cement concrete.

Why Use Industrial 

Materials in Roadways?

Environmental Benefits

Since many industrial materials are used to replace nonrenewable virgin materials that must be mined and processed, 

using industrial materials conserves natural resources and 

reduces the energy use and pollution associated with these 

activities. For example, substituting fly ash (a CCP) for portland 

cement in concrete saves the energy and greenhouse gas 

emissions associated with producing cement. Roads and other 

structures made with industrial materials can be more durable. 

Maintaining and replacing roads less frequently is good for the 

environment because it conserves natural resources and energy.

Economic Benefits

Using industrial materials makes good economic sense for 

project owners and contractors. If industrial material use is 

planned from the beginning, the total project bid cost can be 

lower, allowing the project owner to accomplish more work 

with the same budget. Industrial materials are often less 

expensive than the virgin materials they replace, and recycling 

or reusing materials onsite can reduce material hauling and 

disposal costs. Putting industrial materials such as fly ash to 

use in infrastructure projects also reduces the need for new 

or expanded landfills, saving valuable landfill capacity. 

Performance Benefits

Industrial materials offer significant performance enhancement 

benefits. For example, steel slag, when used as an aggregate 

for asphalt roadway riding surfaces, has a high-friction surface 

that makes driving safer. Using fly ash as a partial replacement 

for portland cement in concrete enhances the durability and 

smoothness of the concrete. Rubber tires used as lightweight 

fill material offer outstanding long-term performance benefits 

and are less expensive than many alternatives. Asphalt 

pavement made with used tires is also more flexible, quieter, 

and less prone to cracking than standard asphalt pavement. 

Green Design

Organizations are encouraging highway construction and 

renovation activities that have a reduced impact on the 

environment. The U.S. EPA, the Federal Highway Administration, 

and the Maryland State Highway Administration sponsor the 

Mid-Atlantic Green Highways Partnership (GHP). The GHP seeks 

to incorporate environmental streamlining and stewardship 

into all aspects of the highway development lifecycle, including 

using industrial materials. Visit www.greenhighways.org

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1 Embankment 

Topsoil on roadside embankments can be 

amended with compost, pulp and paper 

byproducts, FGD material, or steel slag, if soil 

conditions merit. These industrial materials can 

improve the condition of the soil, increase plant 

growth, and reduce runoff. Foundry sand, steel 

slag, and coal ash are suitable for embankment fill.

2 Mechanically Stablizied Earth (MSE) Wall

Retaining walls hold back soil and rock and 

prevent the erosion of roadside slopes; they are 

often made of concrete or modular blocks.

•	Fly ash and ground granulated blast furnace 

slag can be used as partial replacements for 

portland cement in concrete, making the 

concrete stronger and more durable. 

•	 Concrete aggregates can include bottom ash, 

foundry sands, reclaimed concrete, and blast 

furnace slag. 

•	 Portland cement can contain fly ash, FGD 

gypsum, foundry sands, drywall, blast furnace 

slag, and steel slag. 

3 Asphalt Surface

Blast furnace slag, steel slag, and boiler slag 

can replace virgin aggregate in the asphalt 

surface layer.

4 Asphalt Base

Fly ash, bottom ash, foundry sands, and reclaimed 

concrete and asphalt can be used as aggregate in 

the asphalt base layer.

Ground rubber tires and ground roofing shingles 

can be added to the hot asphalt surface and 

base mix, increasing the flexibility and durability 

of the pavement and reducing the need for costly 

virgin asphalt.

5 6 Granular Base and Sub-Base

A variety of industrial materials can be used as 

granular base and sub-base, including: 

•	 Bottom ash

•	Foundry sand

•	 Reclaimed concrete and asphalt 

•	 Glass

•	 Roofing shingles

•	 Blast furnace slag

•	 Steel slag

•	 Scrap tires

Fly ash can also be used as mineral filler in asphalt 

base, granular base, and sub-base. 

7 Subgrade (Original Soil)

Fly ash can be used to improve the structure and 

stability of the subgrade upon which the road will 

be built.

8 Structural Fill

Structural fill supports and relieves pressure from 

retaining walls.

•	 Shredded scrap tires are particularly well suited 

for fill applications; they are lightweight, drain 

well, and resist frost penetration. 

•	Fly ash, reclaimed asphalt pavement, concrete, 

crushed glass, and foundry sand can also be 

used as backfill for retaining walls.

9 Vegetated Swale

One environmentally-friendly way to provide 

adequate drainage for roadways is through 

vegetated swales, which can help improve water 

quality.

•	 Scrap tires, reclaimed concrete or asphalt, 

glass cullet, and blast furnace slag can be used 

in place of traditional drainage materials, such 

as virgin sand or gravel.

Always consult your state and 

local environmental agencies 

to determine approved uses of 

industrial materials.

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The Center for Environmental 

Excellence by AASHTO 

The Center for Environmental Excellence 

(CEE) by the American Association of 

State Highway and Transportation 

Officials (AASHTO) is a one-stop 

resource for transportation officials 

seeking environmental information. 

The comprehensive Web site includes 

tools, information, and case studies on 

recycling and waste management. 

See: http://environment.transportation.org
Case Study

San Francisco Bay Bridge 

Reconstruction Maximizes the 

Use of Fly Ash in Concrete Mix 

Ongoing construction of the new east span of the San Francisco Oakland Bay 

Bridge is taking advantage of the unique properties of fly ash and ground 

granulated blast furnace slag to enhance the durability and strength of the 

concrete used. The California Department of Transportation (Caltrans) started 

the new span in 2002 to replace the old, seismically vulnerable span that was 

damaged in a 1989 earthquake and subsequently repaired. The chemical and 

physical properties of fly ash concrete help mitigate the corrosive effects of 

seawater and salt fog and the structural requirements of an earthquake zone.

The high-salt zones of the bridge will use a concrete mix containing 50% fly 

ash, which prevents cracking as the cement hardens, a common problem in 

a salt-water environment. The round fly ash particles also improve flow and 

workability in the mix. The fly ash concrete used is also denser and stronger 

than traditional concrete and can better carry heavy loads. Caltrans will use 

over 30 concrete mix designs in the new bridge, some containing more than 

50% fly ash. In addition, ground granulated blast furnace slag was used in 

pier columns to improve durability and workability and reduce bleeding. In 

2006, Caltrans received an award for Innovation from EPA’s Coal Combustion 

Products Partnership (C2

P2), in part based on its work on the new Bay Bridge.

Did You Know? 

The American Association of State 

Highway Transportation Officials 

(AASHTO) has developed standards 

for using recycled industrial materials 

in cement and concrete. AASHTO M 

295 and AASHTO M 302 are standard 

specifications for using fly ash and 

ground granulated blast furnace slag 

in cement and concrete in roadways. 

Contact your state or local environmental 

agency for more information about 

approved uses of industrial materials in 

your region. You can also contact your 

state Department of Transportation to 

determine whether they have developed 

specifications for using industrial materials 

in roadways. See the AASHTO Web site 

at: bookstore.transportation.org. See 

also the American Society for Testing 

Materials at: www.astm.org.

EPA’s Industrial Materials Recycling Homepage:

Provides an overview of industrial materials, their 

benefits, and opportunities for reuse and recycling: 

www.epa.gov/industrialmaterials

EPA’s Comprehensive Procurement Guidelines: 

Includes information about construction and 

transportation products containing recycled 

content: www.epa.gov/cpg

Construction Industry Compliance 

Assistance (CICA) Center: Contains a C&D 

materials State Resource Locator, where you can 

find state environmental agency Web sites: 

www.cicacenter.org

The Federal Highway Administration (FHWA) 

Office of Pavement Technology’s Recycling 

Web page: Provides information about current 

projects and activities, research and references, 

publications, and policies pertaining to the use 

of recycled materials: www.fhwa.dot.gov/

pavement/recycling

The Recycled Materials Resource Center 

(RMRC): The RMRC's mission includes 

systematically testing, evaluating, developing 

appropriate guidelines for and demonstrating 

environmentally acceptable increased use 

of recycled materials in transportation 

infrastructure construction and maintenance. 

This Web site provides information on 

recycling and reusing industrial materials in 

roadways: www.recycledmaterials.org

User Guidelines for Byproducts and Secondary 

Materials Use in Pavement Construction: 

Provides information and general guidance 

on engineering evaluation requirements, 

environmental issues, and economic considerations 

for determining the suitability of using recycled 

materials in highway applications: www.

recycledmaterials.org/tools/uguidelines/index.asp

Industrial Resources Council (IRC): Contains 

information about industrial materials and their 

applications. The IRC is composed of industry 

trade associations representing coal combustion 

products, foundry sands, iron and steel slag, 

wood and pulp materials, rubber materials, 

and construction and demolition materials: 

www.industrialresourcescouncil.org

Mid-Atlantic Green Highway Partnership: 

Seeks to incorporate environmental 

sustainability into all surface-transportation 

infrastructure, including using industrial materials: 

www.greenhighways.org

Resources for More Information

Environmental 

Protection Agency 

EPA-530-F-08-024

www.epa.gov 

July 2009

 Recycled/Recyclable—Printed on paper that contains at least 50% post consumer fiber.