Use of warm-mix asphalt pavement has increased 777% increase since 2009. In 2017, about 42% of warm mixes were produced for transportation departments.
Adobe Stock / Fotolia RAW Use of warm-mix asphalt pavement has increased 777% increase since 2009. In 2017, about 42% of warm mixes were produced for transportation departments.

According to the Federal Highway Administration, warm-mix asphalt (WMA) is produced at temperatures 30 degrees to 120 degrees F lower than hot-mix asphalt (HMA). Water-based, organic, chemical, or hybrid additives extend mix working time and slow cooling, thus enabling cold-weather and nighttime placement. The most common technology is plant-based foaming, which injects a small amount of water into the asphalt during production.

European transportation departments have used warm mixes for more than a decade, and 40 U.S. states have approved or are testing mixes. In 2017, 147.4 million tons -- nearly 39% of total asphalt production nationwide -- were produced, according to the National Asphalt Pavement Association (NAPA), which has tracked production of mix types and recycling rates since 2009. More than half of asphalt mixtures in 16 states were warm mixes.

"Road owners are clearly seeing the benefits these technologies bring and are willing to support innovations," says NAPA Chairman Craig Parker.

Nearly 79 million tons of recycled materials — primarily reclaimed asphalt pavement material (RAP) and recycled asphalt roofing shingles (RAS) — were used in new asphalt mixtures last year, similar to the amount used in 2016. This resulted in $2.2. billion in savings compared to the use of virgin materials. More than 76.2 million tons of RAP and nearly 950,000 tons of RAS were used in new mixes, with an additional 3.9 million tons used as aggregate in cold mixes and other road-building activities. At year-end, about 103.5 million tons of RAP and RAS was stockpiled for future use across the country. Reclaiming RAP for use in future pavements saved nearly 50 million cubic yards of landfill space.

The survey gathered results from 229 companies with 1,146 plants in all 50 states, along with data from 32 state asphalt pavement associations. Although national usage estimates weren't calculated, respondents recycled 1.5 million tons of ground tire rubber, slags, cellulose fiber, and other reclaimed and waste materials into nearly 7.5 million tons of asphalt.

“We're creating mixtures through engineering, performance-based specifications, and improved RAP processing,” says NAPA President Mike Acott. “However, there is still room to improve, and we support research and education efforts to keep the use of these mixtures growing.”

A copy of the full survey, including a state-by-state breakdown of data, is available here.

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