Warm Mix Asphalt Update

New Technologies Offer Opportunity for Improved Roadways

Warm Mix Asphalt (WMA) is the name given to conventional Hot-Mix Asphalt (HMA) that is modified by additives or changes in manufacturing processes that allows asphalt mixes to be produced and placed at low temperatures. Reductions of 50 to 100 degrees Fahrenheit have been documented.

WMA technology has now been in the U.S. about 10 years. Since its introduction, millions of tons of WMA have been placed throughout the U.S, and now the California Department of Transportation has become a supporter of the technology.

Efforts to include WMA in California pavement construction began in 2006. After a few internal test trials, Graniterock in partnership with the California Department of Transportation (Caltrans) and the University of California Pavement Research Center (U.C.P.R.C.) entered into a joint research investigation in 2007. Three competing technologies were exhaustively tested at the A.R. Wilson Quarry on test sections designed by the U.C.P.R.C. The purpose of the testing was to determine if the technology impacted the performance of mix in terms of rutting resistance and moisture sensitivity. The testing concluded that there were no major differences between HMA and WMA and that with some minor changes in the lab, the design process would be little changed as well. Since then Caltrans has placed hundreds of thousands of tons of WMA in demonstrations projects and is nearing completion of a final specification for WMA use in the State.

In early 2006 there were only four WMA technologies available in United States. Now there are more than two dozen WMA technologies competing in the market. Currently there are six approved by Caltrans and no doubt more to come over time. Each technology is slightly different so the advantages to the WMA producer and contractor user vary at least a little. At this time Graniterock has not firmly committed to any one, but has developed confidence in at least two technologies through direct lab and field testing.

Recently numerous agencies have shown more keen interest in WMA primarily because it is perceived as a“greener” product than conventional HMA. As WMA does not have to be heated as highly as HMA for workability and compactibility, energy use and emissions from the production process are reduced. Besides the greening property of WMA, senior Caltrans officials and others have recognized that the use of WMA can provide properties that improve the constructability of pavements, particularly those that have been historically more difficult to place. With state mandates for the use of recycled materials such as RAP and rubber, Caltrans has observed that WMA helps contractors with both compaction and smoothness with these more challenging designs.

Graniterock’s interest in the technologies has been driven by how WMA can support customers in building better pavements.Our experience and that of others has demonstrated that WMA offers the contractor-customer a number of benefits:

1. Better workability, even when there is project delay.

2. Smoother and more uniform mats.

3. Serves as a compaction aid for all mixes, and is particularly helpful with stiffer mixes.

4. Can extend the paving season because it can be successfully applied at lower temperatures.

5. Allows for extended hauls without compromising quality.

6. Creates a better working environment for the paving team.

The Hot Mixed Asphalt industry is continually looking for ways to improve, and WMA offers the contractor tools that provide greater flexibility in achieving a high-quality product.