Draft Further Study

Warm Mix Asphalt

December 1, 2015

Project Team

Jessica Schlosser, Air Quality Specialist

Chelsea Gonzales, Senior Air Quality Specialist

Chay Thao, Program Manager

Sheraz Gill, Director of Strategies and Incentives
Warm Mix Asphalt Further Study

i Table of Contents| SJVAPCD

Table of Contents

I. EXECUTIVE SUMMARY.......................................................................................... 1

II. COMMITMENT FROM THE 2012 AND 2015 PM2.5 PLANS................................... 3

III. WARM MIX ASPHALT ............................................................................................. 3

IV. WMA BENEFITS...................................................................................................... 5

V. POTENTIAL EMISSION REDUCTIONS CAN BE NEGATED ................................. 8

VI. CHALLENGES FOR IMPLEMENTING WMA IN THE VALLEY ............................... 9

VII. FURTHER STUDY FINDINGS............................................................................... 12
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1 EXECUTIVE SUMMARY| SJVAPCD

I. EXECUTIVE SUMMARY 

The San Joaquin Valley Air Basin (Valley) faces unique and unprecedented air quality 

challenges in attaining National Ambient Air Quality Standards (NAAQS). The San 

Joaquin Valley Air Pollution Control District (District) must explore all available emission 

reduction opportunities in order to demonstrate attainment for multiple federal ozone 

and PM2.5 standards in the coming years. In an effort to leave no stone unturned, the 

District conducted a study to identify how to best promote lower emission asphalt 

production practices. Using warm mix asphalt (WMA) instead of hot mix asphalt (HMA)

results in lower temperatures required for production, storage, and transport. This can 

lead to less fuel consumption, resulting in potential cost savings and emissions

reductions. The District collaborated with asphalt industry stakeholders and policy 

makers in developing this further study in order to gain an understanding of the use of 

warm mix technologies in the Valley and identify potential opportunities and barriers for 

adoption of this technology. As a result of this effort, the District found the following:

1. WMA is a Potential Alternative to HMA

WMA has been used in Europe since 1997 and the United States (U.S.) since 2002. 

Several iterations of the technology have been developed for a variety of road 

applications. Case study results suggest that WMA performance can be equal to or 

better than that of HMA in certain instances, although more evidence will be required 

to demonstrate its reliability in climates like the Valley.

2. WMA Offers Benefits Compared to HMA

Although switching from HMA to WMA may require plant modifications, more precise 

moisture control in some cases, and an overall higher cost, WMA offers benefits 

over HMA including:

 Potential reduced fuel consumption

 Improved performance during paving in cooler climates

 Extended transportation and compaction window

 Safer working conditions

3. Potential Emissions Reductions Can be Negated

Using WMA instead of HMA shows promise for reducing emissions associated with 

the production of asphalt. Lower temperatures required for production, storage, 

transport, and application translates to potentially lower fuel consumption, which 

could lower the emissions associated with the fuel consumed. Additionally, lower 

temperatures could result in lower direct emissions of volatile organic compounds 

(VOCs) at the work site. However, the emissions reductions from fuel savings could 

potentially be negated in certain long haul transport cases. In order to extend the 

hauling benefit, WMA could be heated to HMA temperatures in order to keep the 

material workable for even longer periods of time, thus reducing the fuel savings and 

eliminating potential emissions reductions. 
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2 EXECUTIVE SUMMARY| SJVAPCD

4. WMA has Several Challenges in the Valley

While the WMA markets are developed and growing in other states, there are still 

several uncertainties that may limit the adoption of WMA technologies in the Valley. 

Some of these barriers include:

 Uncertainties in performance with WMA in the Valley

o Insufficient number of pilot projects to demonstrate viability in the Valley

o Durability demonstration

o Longevity demonstration

 Poor cooling in the Valley’s hot summer climate

o More time required to cool to necessary temperature

o Longer periods of road closures due to increased cooling time

o Increased costs due to longer periods of road closures

 Lack of accepted WMA specifications and guidelines in California

o Lack of awareness of WMA

 Lack of confidence in WMA

 Higher cost associated with WMA 

o Retrofit or new equipment required

o Additional cost of chemical additives

 Low demand

Based on the above findings and in order to continue evaluating and promoting the use 

of WMA in the Valley, the District recommends the following:

1. Encourage additional pilot projects to assess viability and life cycle of 

WMA in the Valley. 

2. Encourage Caltrans to further develop WMA specifications. 

3. If found to be feasible in the Valley, work with stakeholders to educate and 

encourage WMA usage as a means of implementing additional pilot 

projects. 

4. Meet with stakeholders as necessary.

5. If found to actually reduce emissions and be feasible, consider including 

WMA as an ISR mitigation measure. 
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3 COMMITMENT FROM THE 2012 AND 2015 PM2.5 PLANS| SJVAPCD

II. COMMITMENT FROM THE 2012 AND 2015 PM2.5 PLANS

Liquid asphalt production and paving in the Valley contributes 0.160 tons per day (tpd)

of oxides of nitrogen (NOx) emissions across the entire Valley. While these emissions 

are low and do not significantly contribute to elevated PM2.5 levels in the Valley, the 

District has adopted a “no stone left unturned” policy when identifying potential emission 

reduction opportunities. As such, the District made a commitment in the 2012 PM2.5 

Plan and 2015 Plan for the 1997 PM2.5 Standard (2015 PM2.5 Plan) to evaluate the 

feasibility of WMA as an alternative to HMA to reduce NOx emissions from this source 

category. This further study includes the following elements:

1. Evaluate opportunities to further encourage transportation and county agencies 

to continue transitioning from HMA to WMA as feasible. As part of this 

evaluation, the District will explore the potential feasibility of additional control 

measures and granting mitigation credits for WMA usage through the District’s 

Indirect Source Review (ISR) program.

2. Evaluate potential outreach and education opportunities for encouraging project 

developers/construction managers to increase their adoption and implementation 

of WMA.

This study was conducted with significant interaction and input from stakeholders, 

including asphalt pavement plant operators, road construction companies and 

contractors, county and city planning departments, pavement plant consultants, and 

state and federal policy makers.

On October 8, 2015, District staff held a kick-off meeting with several members of the 

local California Department of Transport (Caltrans) district, a representative from a local 

pavement production facility, and an experienced local public works engineer. This 

initial meeting gave insight into the regional issues that affect the adoption of WMA

technologies here in the Valley and shed light on WMA barriers that were not addressed 

in the District’s extensive literature review. Meeting attendees were also helpful in 

providing the District with additional contacts for further investigation. On October 28, 

2015, the District conducted a larger and more comprehensive meeting with members 

from public works departments, local pavement plants, California Asphalt Pavement 

Association (Cal APA), Caltrans, Federal Highway Administration (FHWA), California Air 

Resources Board (CARB), and the Environmental Protection Agency (EPA). Following 

a presentation by District staff, attendees were asked a number of questions regarding 

their experiences with WMA. Through extensive stakeholder input during and following 

these meetings, the District was able to assess the challenges that still must be 

overcome before promoting WMA in the Valley. This report discusses the 

technological, economical, and practical efficacy of WMA use throughout the Valley. 

III. WARM MIX ASPHALT

Asphaltic concrete is used worldwide for road construction. An asphaltic concrete mix 

consists of aggregate and liquid asphalt. The aggregate is comprised of rocks of 

varying size, angularity, and hardness. Liquid asphalt is a natural hydrocarbon 
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4 WARM MIX ASPHALT| SJVAPCD

substance primarily derived from the heaviest part of petroleum crude oil and is used to 

bind the aggregate to create a strong, durable material for an assortment of road 

conditions. The final mixture is brought to the construction site, poured, and compacted 

to become highways, roads, and parking lots.

The durability and longevity of the final pavement product depends on the asphalt 

mixture components and the quality of compaction during the final paving stages. In the 

end, all asphaltic concrete must meet a host of construction specifications (specs), 

which can vary depending on the type of road. These specs can include a certain

temperature, density, and smoothness of the road required by state or local regulations. 

To achieve these specs, contractors must ensure a high level of control when pouring 

and compacting the asphaltic concrete. This control is reliant on the quality and 

workability of the asphalt mixture. 

Conventional road asphaltic concrete is unworkable at ambient temperatures. Heating 

the asphalt mixture to temperatures greater than 300°F (>150°C) temporarily reduces 

the viscosity (the “thickness” of the liquid) and allows for mixing, pouring, and 

compacting of the material. This mixture is appropriately deemed hot mix asphalt 

(HMA) due to the hot temperatures needed during production and paving. The primary 

emissions source from asphaltic concrete production comes from the combustion of the 

diesel or natural gas fuel used to heat the dryers, hot bins, and mixers to these extreme 

temperatures. 

In order to reduce fuel costs, European and American companies developed several 

techniques, collectively known as warm mix asphalt (WMA), to increase the workability 

of asphalt by lowering the viscosity at temperatures as much as 100°F below that of 

HMA. The lower temperatures require less fuel and therefore have the potential to 

decrease emissions from asphalt production. The use of WMA in the U.S. has been 

growing steadily since the first test section was completed in 2004 at Auburn 

University's National Center for Asphalt Technology (NCAT)1. In 2012, WMA 

represented an estimated 30% of the total asphalt market in the U.S. FHWA has 

chosen WMA for rapid deployment under its Every Day Counts (EDC) initiative. The 

EDC initiative is, “designed to identify and deploy innovation aimed at reducing the time 

it takes to deliver highway projects, enhance safety, and protect the environment.” 

WMA Techniques

WMA is defined as an asphalt mixture that is produced at a temperature of 270 ̊F or 

less. In order for WMA to be workable at these lower temperatures, it is formed using 

one of two different techniques. The first technique is mechanical alteration of the 

asphalt properties. Mechanical methods include, but are not limited to, adding watercontaining products or water-based foaming processes to the mixing step during asphalt 

production. Water foaming is the most common of the mechanical techniques and has 

been used in various WMA applications throughout the nation. All mechanical methods 

require some plant modifications, including adding new equipment and changing 

 

1

“Public Roads” FHWA. Retrieved from: https://www.fhwa.dot.gov/publications/publicroads/10julaug/05.cfm
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5 WMA BENEFITS| SJVAPCD

production practices. Mechanical methods for WMA have been shown to reduce the 

production temperature by 0-35°F.

2

 

The other technique for WMA production is the addition of chemicals in order to alter the 

asphalt properties. Chemical additives include, but are not limited to, organic wax, 

cationic surfactants, surface-active agents, processing aids, and polymers. Additive 

dosages range from 0.2% to 3% by mass or weight. Chemical additives for WMA have 

been shown to reduce the production temperature by 10-100°F. 2 While the transition to 

the mechanical WMA methods require change to the production facility, requiring 

additional investments, the use of additives can be accommodated with minimal 

alteration to existing asphalt plant and production technology. However, with this 

technique, additives would be used in every batch and would still result in increased

production costs.

In addition, both WMA technologies generally require more finesse in controlling 

moisture in the aggregate and in the overall system operation, such as tuning of the 

burner to run efficiently at lower temperatures. This requires training and education of 

operators and engineers before transition to WMA production at any HMA facility.

IV. WMA BENEFITS

WMA has been used in the U.S. for over a decade primarily for fuel cost savings and 

other reasons beyond air pollution control. Ongoing lab studies, accelerated pavement 

testing, and field testing have guided the implementation of WMA in California. Since 

2010, Caltrans and the University of California Pavement Research Center have been 

evaluating WMA technology and its performance by testing the rutting and cracking 

performance, moisture sensitivity, durability, aging, and stability of multiple WMA 

products.

3

In the controlled testing environment, WMA has been shown to have equal 

or better overall performance, increased workability, potential energy savings, and safer 

working conditions compared to HMA.

Improved Performance in Cooler Climates

WMA provides improved workability and easier pavement compaction, which is critical 

to long-term performance of the road.

4

In cooler climates, this longer compaction 

window and slow cooling time provides superior in-place density, which is one of the 

most important metrics of a successful pavement project. Asphalt becomes more 

workable as the viscosity decreases. Figure 1 is a plot of viscosity as related to 

temperature for two different asphalt mixtures. The compatibility range of an asphalt 

mixture is a measure of the range of temperatures during which the material is able to 

be rolled to the final density and smoothness specs prior to cooling and opening for 

 

2 Asphalt Pavement Association of Michigan Presentation. Retrieved from: http://www.apa-mi.org/docs/2013LRWWarmMixAsphalt.pdf

3

Jones et al. Research Findings on the Use of Warm-Mix. Retrieved from: http://ra-foundation.org/wp-content/uploads/2013/02/040-

PAP_060.pdf

4 MyAsphaltPavingProject.Com. (2011). “What are the Specifications?” Retrieved from 

http://www.myasphaltpavingproject.com/whatisasphalt/what-are-the-specifications
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6 WMA BENEFITS| SJVAPCD

traffic operations. Conventional HMA, labeled in the figure as “Liquid AC,” is 

compactible only at higher temperatures. The WMA, labeled as “Foamed AC”, has a 

larger compactability range.

Figure 1 Viscosity of Two Asphaltic Concrete (AC) Mixtures Plotted Over a Range 

of Production Temperatures 5

Safer Working Conditions

The lower mixing and paving temperatures of WMA has the potential to minimize visible 

smoke and odor emissions. These emissions consist of particulate matter, CO2, and 

VOCs. One study indicates that fumes released at the paving site are reduced at a rate 

of 50% for each 10 ̊C. 6 The lower temperatures also create cooler working conditions 

for the asphalt workers. Less fumes and odor reduces the public nuisance of placing 

asphalt and improves worksite safety for the construction team. 

Extended Transport Time

WMA allows for longer (slower) cooling periods than HMA. Slower cooling means the 

material can be hauled longer distances or compacted during a longer window of 

opportunity before the material begins to become too viscous and unworkable. 

Improved hauling time allows the material to be transported to more remote locations 

and introduces more flexibility in transportation schedules. Additionally, a longer cooling 

window allows the material to be compacted at safer, lower temperatures for a longer 

period of time. 

 

5 Astec Products Brochure (2015). Retrieved from: http://www.astecinc.com/products/liquid-additives/warm-mix-systems.html

6

 EAPA (2010). Retrieved from: http://www.eapa.org/usr_img/position_paper/the_use_of_warm_mix_asphalt_january_2010.pdf
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7 WMA BENEFITS| SJVAPCD

Potential Energy and Cost Savings 

By lowering the production, storage, transport, and placement temperatures, 

manufacturers require less fuel to heat aggregate and liquid asphalt. These energy 

savings can potentially offset the cost of additives or needed modifications to plants, 

especially where energy costs are high. Reduced plant temperatures may also cause 

less wear on plant equipment, thus reducing plant maintenance costs. 7

Assessments outside of the Valley have shown potential for reduced costs. Although 

production facilities must modify some aspects of their plant by installing additional 

equipment in order to accommodate WMA technologies, the hauling, laydown, and 

compaction equipment do not need to change. The initial incremental cost of WMA 

over HMA is primarily due to the foaming equipment or additive chemicals used at the 

time of production. Over time, as WMA demand increases, the cost and fuel savings 

associated with WMA has the potential to outweigh the cost to purchase the WMA 

technology. 

Additionally, the low temperatures used in WMA production allows for higher 

percentages of recycled highway materials to be used in the mixture with no effect on

ultimate pavement performance. This type of mixture is called reclaimed asphaltic 

pavement (RAP).

8

The low temperatures of WMA result in less aging of the old 

recycled material, so a larger ratio of reclaimed aggregate can be used to meet the 

same aging properties as HMA with recycled aggregate. The use of RAP is less 

expensive than producing an asphalt mixture completely from raw materials, and 

additional savings can be generated from avoiding landfill disposal or recycling fees. 

The cost savings gained from using RAP could potentially further offset costs for 

additives or required plant modifications needed for WMA production. Fuel savings, an 

increase in reclaimed asphalt pavement content, and reductions in fuel and labor during 

the process of installing WMA could translate to reduced costs for WMA projects over 

time. 

Potential Emissions Reductions 

Table 1 shows an estimate of the maximum potential NOx emissions reductions as a 

result of the complete transition from HMA to WMA at all asphalt production sites in the 

Valley. This estimate is not intended to reflect an estimate of realistic potential 

emissions reductions given the lack of information and potential implementation issues 

associated with converting from HMA to WMA. The District’s 2017 emissions inventory 

from the 2015 PM2.5 Plan estimates 0.160 tpd of NOx emissions from asphalt 

production at all 19 asphalt production facilities in the Valley. While fuel savings for 

WMA at production facilities have been reported to be from 20% to over 50% for some 

WMA technologies, U.S. studies have reported actual burner fuel savings of zero to 

 

7 Caltrans. (2013, April). Caltrans Activities to Address Climate Change: Reducing Greenhouse Gas Emissions and Adapting to 

Impacts. Retrieved from: http://www.dot.ca.gov/hq/tpp/offices/orip/climate_change/documents/Caltrans_ClimateChangeRprtFinal_April_2013.pdf

8 Canadian Asphalt Institute Presentation (2009). Retrieved from: 

http://www.captg.ca/docs/pdf/09presentations/Wednesday%20PM/Warm%20Mix%20Asphalt_Sandy%20Brown.pdf
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8 POTENTIAL EMISSIONS REDUCTIONS CAN BE NEGATED| SJVAPCD

40%, with the average typically around 30%.9 If every plant changed completely from 

HMA to WMA, there would be an estimated 0.048 tpd in NOx emissions reductions 

Valley-wide. This is a small potential emission reduction opportunity, especially 

considering the investments asphalt plants would have to incur to allow for the 

production of WMA at their plants. 

Table 1 Potential Emissions Reductions if all Valley Plants Changed all HMA to 

WMA

Estimated Reductions

Hot Mix Asphalt (Production only)

projected 2017 0.160 tpd NOx

Possible Average Fuel Savings 30%

Maximum Reductions 0.048 tpd NOx

Potential GHG Reductions

In response to climate change objectives, Caltrans included WMA in an April 2013 

report as an activity to reduce GHG emissions and adapt the state’s transportation 

system to prepare for the impacts of climate change. As stated in this report, Caltrans 

identified that WMA can reduce production temperatures by 35-100°F compared to 

conventional HMA, potentially yielding 30% fuel savings and an 18% reduction in the 

overall GHG emissions associated with manufacturing, mixing, and laying the asphalt.

V. POTENTIAL EMISSIONS REDUCTIONS CAN BE NEGATED

While emissions reductions are possible due to the fuel savings benefits of WMA, these 

reductions could be negated if standard WMA production temperatures are exceeded.

During the District’s research, asphalt production and paving experts stated that 

contractors around the state have requested WMA be heated to high temperatures for 

the purpose of extending transport time. WMA is already ideal for long transport due to 

the longer cooling period, so contractors ordering asphalt for remote locations take 

advantage of this property and attempt to further extend the hauling benefit. In this 

case, the WMA would be produced at HMA temperatures in order to keep the material 

workable for longer periods of time. This practice eliminates the fuel savings and leads 

to no difference in emissions from HMA. Any fuel or emissions savings will not be 

realized if there is no consistency in practice in keeping the temperatures lowered. 

While transportation emissions should be the same regardless of material properties, 

the use of WMA for longer hauling distances may actually produce more emissions

overall compared to HMA from the additional truck miles generated. With the initial

 

9

http://www.warmmixasphalt.com/submissions/may2009/08_Marks_wmatwgprovidence.pdf
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9 CHALLENGES FOR IMPLEMENTING WMA IN THE VALLEY| SJVAPCD

limited number of Valley asphalt facilities producing WMA, contractors intending to use 

the material may need to travel further for WMA than HMA. The probability of longer 

hauling distances combined with the possibility of heating WMA to hotter temperatures 

may negate and actually increase emissions associated with the use of WMA compared 

to HMA. 

VI. CHALLENGES FOR IMPLEMENTING WMA IN THE VALLEY

There are several advantages of WMA over HMA, as demonstrated by successful WMA 

installation in many parts of the U.S. However, the District has identified a number of 

barriers for the adoption of WMA technology in the Valley based on extensive input from

asphalt producers and road paving experts.

Uncertainties in Performance with WMA in the Valley

Caltrans has been involved in a number of WMA performance studies since 2012,

leading to a steady increase in adoption of WMA technology in some parts of the state. 

However, there are still a number of uncertainties in construction operations and

pavement performance that limit WMA use here in the Valley. The ability of WMA to 

decrease fuel consumption and improve worksite conditions has been demonstrated in 

controlled environments and cooler climates, but there have been an insufficient 

number of studies to demonstrate viability in the Valley.

There have only been two Caltrans pilot projects for WMA in the Valley. One such 

project was a 5 mile stretch of highway laid on a hot day in 2014 in Kings County. After 

rolling out the material, the asphalt took much longer to cool and resulted in difficult 

compaction and extended lane closures, which significantly increased project costs. 

More pilot projects are critical to identifying these and other Valley-specific problems. 

These uncertainties in paving operations and durability performance in the Valley

extend to long-term concerns. Because WMA is relatively new, a full life cycle analysis 

has not yet been assessed here in California. While there are experiments that have 

simulated long-term erosion of WMA, the longevity and durability of WMA in the Valley’s 

unique climate is unknown. If longevity of the WMA product is not known, the cost and 

emissions benefits cannot be assessed properly. For example, if a road paved with 

WMA has to be repaved earlier than it would have with HMA due to accelerated aging 

or poor durability, the emissions associated with that additional round of paving would 

offset any reductions achieved with WMA production. Depending on the difference in 

lifecycle, the WMA could actually have more lifetime emissions than HMA. While 

experiments indicate that this is not likely, Valley contractors and public works agencies 

will not transition to WMA until more is known about performance in the Valley.

Poor Cooling in the Valley’s Hot Summer Climate

Laying WMA in high heat can lead to poor compaction and delayed cooling. The 

difference in temperature between the ambient air and the asphalt mixture affects the

rate of cooling. Reducing that temperature difference allows for longer (slower) cooling 
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10 CHALLENGES FOR IMPLEMENTING WMA IN THE VALLEY| SJVAPCD

periods and is part of what makes WMA a superior material to HMA in most uses. In 

addition, slower cooling means the material can be hauled longer distances and 

compacted at safer, cooler temperatures for a longer window of time. However, if that 

temperature difference is too small due to hot ambient temperatures, the material may 

not properly set or completely cool to the temperature approved for traffic use. 

Unfortunately, Valley summers are some of the hottest in the State, often reaching 

temperatures well above 100°F. Waiting for the asphalt to cool during typical Valley 

summer days can also cause significant project delays resulting in increased costs and 

longer periods of road closures. Pavement plant operators who participated in the 

WMA study session indicated that almost all of the WMA orders their company receives 

are for Central Coast or Bay Area construction projects, places with cooler climates. 

Until clear WMA specs are written and the use of this material is more widely 

implemented by Caltrans in the Valley, public works and other local agencies will not 

readily adopt WMA technologies.

Lack of Accepted WMA Specifications and Guidelines in California

One necessary step to reducing uncertainties in WMA is to identify effective and safe 

WMA practices and ensure the materials are suitable for a variety of conditions. This 

research is commonly done through Caltrans conducting iterative pilot projects 

throughout various climates and conditions. While it takes years to complete each of 

these state-funded Caltrans projects, these are necessary in order to write new specs 

and promote the safe, easy use of a new material.

Most public and private agencies follow the Caltrans specs when constructing or 

maintaining roads. These agencies, including city and county public works 

departments, rely heavily on the Caltrans specs for operational guidance. Since 2012, 

Caltrans has tested and approved a growing list of WMA techniques and materials listed 

in the paving specs as available options for contractors. While the Caltrans specs 

identify WMA materials as an option, they do not contain the detailed procedures 

necessary for implementing WMA projects.10 There is no differentiation in the specs 

between certain HMA and WMA practices; the section in which one can find any WMA 

information is titled “HMA Specifications.” Unclear specs can be confusing and 

misleading. Without WMA-specific procedures, contractors ultimately decide to pave 

with HMA, a familiar product that has been tested and handled in a variety of situations. 

Since proper handling of WMA can make a significant difference in the fuel and 

emissions reductions realized during a project, it is critical to have unified WMA specs in 

order to achieve the economic and environmental benefits.

Lack of Confidence in WMA

The District found that one of the largest barriers to adoption of WMA in the Valley is the 

lack of confidence in the technology and its potential benefits, especially when used 

with other technologies. 

 

10 Caltrans Section 39 HMA Specifications. Retrieved from: http://calapa.net/section_39.html
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11 CHALLENGES FOR IMPLEMENTING WMA IN THE VALLEY| SJVAPCD

As an example, the District learned from stakeholders involved in this study that WMA 

use could clash with the state mandate that Caltrans use rubberized asphalt. This 

mandate is derived from a provision in Assembly Bill 338 (Levine) which requires 

Caltrans to use a minimum of 35% Crum Rubber Asphalt (CRA)11 as paving material. 

CRA is a HMA mixture in which recycled rubber is added as an aggregate in order to 

reduce sound (when driving) and increase stability. This technique is cost effective and 

environmentally friendly due to rubberized asphalt’s better aging properties and greater 

durability.

12

 The rubber used in the mixture typically equals 3 recycled tires per ton, 

which can mean approximately 2,000 recycled tires per lane mile for a road overlay 

project. 13 While CRA is a green technology, stakeholders attending the District’s WMA 

study meetings voiced concerns over the use of rubber in the WMA mixture until 

rubberized asphalt is fully understood or exhaustively tested.

These concerns were raised even though Caltrans conducted a large study in 

conjunction with the UC Pavement Research Center and tested the performance of 

WMA made with rubberized aggregate. This study reported that there was not a 

significant difference in performance between rubberized WMA and HMA. However, 

none of the projects in the UC Pavement study took place in the Valley, which has 

contributed to the concerns and uncertainties by Caltrans and local contractors 

regarding the implementation of WMA in this region.14 Education and outreach 

regarding these studies about the performance and benefits of WMA may assist in

increased use of WMA in the Valley, but ultimately additional pilot tests in Valley 

locations are necessary in developing WMA specs and instilling confidence in the

pavement contractors and regional Caltrans staff.

Higher Cost Associated with WMA in the Valley

The incremental cost of producing WMA is a barrier to production facilities and end 

users. Mechanical methods for WMA production, like water foaming, require some 

plant modifications, including adding new equipment and changing production practices,

which can lead to high up-front costs associated with WMA production. Similarly, while 

the use of chemical additives can be accommodated with minimal alteration to existing 

asphalt plant production technology, the chemicals or materials can be costly and are 

used in every batch, nonetheless increasing the overall cost of WMA. Additionally, each 

facility must incur the cost of transition training and education of operators and 

engineers in order to successfully expand their operation to incorporate WMA. Finally, 

pavement plants must pay to obtain new permits for any new tanks. 

The added costs of WMA production are incorporated in the final cost of the material to 

the end user.15 With most Valley agencies operating on a tight budget in low-income 

 

11 AB 338 (Levine) (2005) Retrieved from: http://www.leginfo.ca.gov/pub/05-06/bill/asm/ab_0301-

0350/ab_338_cfa_20050427_134930_asm_comm.html

12 Alameda County COG Presentation (2013). Retrieved From: 

http://www.acgov.org/sustain/documents/roundtable_rubberasphalt_gci.pdf

13 Alameda County COG Presentation (2013). Retrieved From: 

http://www.acgov.org/sustain/documents/roundtable_rubberasphalt_gci.pdf

14 http://www.dot.ca.gov/newtech/researchreports/reports/2013/final_report_task_2385c.pdf

15 Asphalt Pavement Association of Michigan Presentation. Retrieved from: http://www.apa-mi.org/docs/2013LRWWarmMixAsphalt.pdf
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12 FURTHER STUDY FINDINGS| SJVAPCD

communities, it could be difficult for these public entities to choose WMA over 

conventional HMA when the cost difference is $0.50-5.00 more per ton. While most 

Valley operators who participated in this study indicated that they may be able to 

overcome these incremental costs, they could not do so without an increase in demand.

Low Demand

Due to uncertainties about the performance, longevity, operational procedures, and 

associated costs, WMA is not yet widely requested or ordered by asphalt plants. As 

such, very few Valley asphalt plants produce WMA. Until there is widespread request of 

the material, pavement plants have very little incentive to begin large-scale WMA 

production. As long as the demand for WMA remains low, the cost to purchase will be 

$0.50-5.00 more per ton than HMA (at an overall $60-80 per ton). Since contracts for 

road construction projects go to the lowest bidder, it is difficult for production facilities 

and contractors to promote WMA use when the competition is selling cheaper material,

no matter the other benefits WMA has to offer.

VII. FURTHER STUDY FINDINGS

This study has found that WMA has the potential to reduce emissions by using less fuel 

and the potential to provide safer conditions by producing less odor and fumes.

However, this potential reduction in emissions must be further evaluated given that a 

number of other factors with respect to implementation may negate and actually 

increase emissions associated with WMA.

In other states and countries, WMA has shown to be a feasible alternative to HMA and 

continues to grow steadily due to performance and cost-savings advantages. However, 

in the Valley, many barriers still remain. Poor paving performance in the Valley’s high 

summer heat, lack of confidence in WMA technology, an insufficient number of pilot 

projects to support feasibility in the Valley, lack of Caltrans WMA specifications to 

support proper WMA usage, and not enough demand to provide the needed economies 

of scale to achieve the identified cost benefits have all hindered widespread adoption of 

WMA throughout the Valley.

In order to continue evaluating and promoting the use of WMA in the Valley, the District 

recommends the following:

1. Encourage additional pilot projects to assess viability and life cycle of 

WMA in the Valley. Promote and support additional WMA pilot projects in the 

valley to reduce uncertainty and improve confidence in the performance and 

benefits (including emissions reductions) of WMA.

2. Encourage Caltrans to further develop WMA specifications. Encourage 

Caltrans to develop WMA specs to provide the appropriate guidance to 

contractors and public work agencies.
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13 FURTHER STUDY FINDINGS| SJVAPCD

3. If found to be feasible in the Valley, work with stakeholders to educate and 

encourage WMA usage as a means of implementing additional pilot 

projects. Continue to meet with public works agencies, including Caltrans, to 

help educate and encourage WMA use. The District could also provide WMA 

literature and information during the permitting process at various pavement 

plants or through the ISR process for construction projects that require paving as 

a means of implementing additional pilot projects.

4. Meet with stakeholders as necessary. Continue to meet with Caltrans, Cal 

APA, plant operators, and other pavement industry leaders to assess feasibility 

and emission reductions. If found to be feasible and to result in actual emission 

reductions, identify challenges and look for solutions for adoption of WMA 

technology. 

5. If found to actually reduce emissions and be feasible, consider including 

WMA as an ISR mitigation measure. District Rule 9510, Indirect Source 

Review (ISR), requires developers of larger residential, commercial and industrial 

projects to mitigate smog-forming and particulate emissions generated by their 

projects. If WMA is found to actually reduce emissions and be feasible, the 

District could consider allowing the use of the emission reductions achieved by

using WMA in place of HMA to mitigate project emissions.