What is WMA?

Warm mix asphalt (WMA) is the generic term 

for a variety of technologies that allow asphalt 

mixtures to be produced, transported, placed, 

and compacted at lower temperatures. WMA 

technologies typically result in temperatures 30 to 

75 degrees Fahrenheit lower than traditional hotmix asphalt (HMA). Because less energy is needed 

to heat the asphalt mix, in many cases, less fuel 

is required to produce WMA. Fuel consumption 

during WMA production may be reduced 

by 20 percent with proper production plant 

modifications. It is a proven technology that can:

• Improve compaction that improves 

 pavement performance.

• Reduce fuel or energy usage.

• Improve worker comfort by reducing 

 exposure to higher temperatures, fuel 

 emissions, fumes, and odors.

In addition, WMA technologies allow asphalt 

mixtures to be hauled longer distances and can 

extend the paving season due to WMA’s ability to 

maintain workability at lower temperatures. The 

proper use of WMA may result in reduced overall 

paving costs. 

WMA Technologies

Warm Mix Asphalt 

Technologies

FAQs

What makes WMA different from traditional 

HMA? 

High production temperatures are traditionally 

needed to make the asphalt binder fluid during 

mixing to completely coat the aggregate and also 

have good workability during hauling, placement, 

and compaction. WMA technologies use chemicals, 

waxes, organic additives, water-bearing minerals, 

water or a combination of technologies. These 

technologies allow the asphalt binder to remain 

fluid at lower temperatures during mixing in order 

to completely coat the aggregates. It is the use of 

these technologies that allow the construction of 

asphalt pavements at lower temperatures.

Does using WMA require plant and mix design 

modifications? 

The need for plant and mix design modifications 

depends upon the type of additive used. Most 

require relatively simple plant and mix design 

modifications to introduce the temperaturereducing technologies into either the mixture or 

asphalt binder stream. Some technologies are 

added to the asphalt binder by the supplier and 

do not require additional equipment at the plant. 

Other technologies require more substantial 

modifications. Technologies involving water-based 

foaming techniques or mixture additives require 

additional equipment installed at the plant to 

measure and deliver the additive. 

Does WMA impact plants that produce the 

asphalt mixtures? 

HMA plant modifications and/or operational 

changes are typically needed to utilize WMA 

technologies effectively and optimize the benefits 

WMA can provide. By making the necessary 

operational changes and plant modifications 

lower mixing temperatures can be successfully 

used, resulting in reduced emissions and odors. 

Depending on the production temperature 

and plant efficiency, a range of 15 to 40 percent 

reduction of carbon dioxide and other emissions 

during production have been reported.

Contact Information

For training or more information on 

this Every Day Counts Initiative, please 

contact your local FHWA Division Office. 

To learn more about EDC, visit: 

http://www.fhwa.dot.gov/everydaycounts

Crew applying WMA near Spring Mills, PA.

About Every Day Counts

Every Day Counts is designed to identify 

and deploy innovation aimed at shortening 

project delivery, enhancing the safety 

of our roadways, and protecting the 

environment.
Quick Facts

• WMA technologies allow asphalt mixtures to be 

produced, transported, placed, and compacted at 

lower temperatures.

• WMA technologies allow for production and 

placement of asphalt mixtures at temperatures 

30 to 75° F lower than conventional HMA 

technologies.

• WMA technologies fall broadly into one of five 

general categories: materials processing, organic 

additives, chemical additives, foaming processes, 

and hybrid systems that combine multiple 

technologies.

• WMA technologies improve compaction which 

leads to improved pavement performance.

• Producing WMA can reduce energy consumption 

during the manufacture of asphalt mixtures up to 

20 percent with proper production operations and 

plant modifications. 

• WMA reduces visible and non-visible emissions, 

fumes, and odors, improving working conditions.

• WMA reduces carbon dioxide (CO2) emissions 

through reducing the amount of fuel required to 

produce asphalt mixtures. 

• Recycled asphalt pavement (RAP) can be used 

with WMA, reducing costs and use of raw 

materials. 

• WMA can be placed and compacted in cooler 

ambient temperatures, providing an extended 

paving season.

• WMA can be adapted to various traffic levels, 

temperatures, and materials required for a given 

project. 

• The first public demonstration of WMA in the 

United States was in 2004. As of 2009, WMA 

projects were constructed in more than 40 States, 

and at least 14 States have adopted specifications 

that allow WMA. 

How Does It Work?

WMA technologies enhance mixture workability 

through the addition of additives (organic, chemical, 

water-based, or hybrids). Asphalt mixtures are 

primarily composed of aggregates and asphalt 

binder. Aggregates are hard materials such as 

crushed stone. Asphalt binder is a dark brown 

to black, sticky liquid that holds together the 

aggregates when mixed. Some WMA technologies 

work by reducing the viscosity, which increases 

the ability to flow or pour the asphalt binder. This 

allows the aggregates to be properly coated with 

asphalt binder at lower temperatures. WMA also 

improves workability during construction allowing 

the mixture to be properly transported, paved, 

and compacted at lower temperatures. Proper 

compaction provides increased pavement density 

and is necessary for pavement performance.

One drawback of HMA is that, in cooler climates and 

during long distance truck transport from the plant 

to the paving site, the HMA mixture temperature 

drops rapidly and may not retain its workability. 

WMA technologies help maintain workability at 

lower temperatures to allow successful placement 

of WMA mixtures in lower temperatures and longer 

trucking distances. As a result, WMA technologies 

may extend the paving season in cold temperature 

regions and assist night paving at lower ambient 

temperatures. Night paving is increasingly used 

on projects, especially large scale projects located 

in or near cities, to minimize traffic disruption and 

congestion.

Better Compaction Improves 

Performance

Proper compaction is critical to well-performing 

pavements. One indication of proper compaction 

is the final density of the asphalt pavement. In fact, 

most federally funded highways paved with asphalt 

are accepted based on density. WMA is a compaction 

tool that can help achieve more uniform density and 

improve pavement performance.

WMA’s ability to improve compaction is versatile. It 

has been used successfully in a range of pavement 

thicknesses; and similar to traditional HMA, when 

properly designed, is durable enough to withstand 

high traffic demands. WMA has been used in all 

types of asphalt concrete: dense-graded, stone 

matrix, and porous asphalt mixtures. Multiple WMA 

technologies are available, so the choice can be 

adapted to the temperatures and materials required.

Good for Workers, Good for the 

Environment

Working conditions are more comfortable with WMA. 

Both at the production plant and on the construction 

site, workers experience cooler working temperatures 

and reduced fumes, haze, and odors. Comments 

from workers have been highly positive. According 

to Brad Neitzke Materials Engineer for FHWA, Western 

Federal Lands Highway Division: “Certainly, warmmix improved working conditions at the paving site. 

The construction crew’s first reaction was to say, 

‘There’s no fumes!’ ”

With reduced fuel or energy usage, reduced emissions, 

and combined with the use of recycled asphalt, WMA 

minimizes negative impacts to the environment by 

reducing the use of natural resources and improving 

air quality. In fact, WMA technologies may make it 

possible for asphalt production and paving to be 

done on days when the air quality in and around 

nonattainment areas would typically put a halt to 

traditional HMA paving.

Researcher verifying the temperature of the mixture. Crew applying WMA in Yellowstone National Park.

Blue haze and fumes 

produced by HMA.

Blue Haze and fumes 

reduced when WMA 

is used.

Completed WMA road in Yellowstone National Park.