ForConstructionPros.com

The future of hot mix asphalt might be cooling down a little bit...to warm mix asphalt. Warm mix asphalt (WMA) is an asphalt mix with an additive that allows the asphalt to be mixed and placed at cooler temperatures, says Annette Smith, project leader, Warm Mix Asphalt Technology Group, PQ Corp. "Not cold temperatures but usually between 50˚F to 75˚F cooler than you would typically make a hot mix asphalt," she says.

The background
Warm mix asphalt initially started in Europe but made its way over to the United States around 2003-2004, Smith says.

The benefits of WMA are numerous. First, and one of the main reasons warm mix asphalt was created, is lower emissions. "Depending on the type of emissions you can reduce it up to 65%," Smith says. "There are reductions in emissions not only at the plant where they manufacture the asphalt but also behind the paver."

Contractors who use WMA to pave also benefit from the ability for longer hauls -WMA asphalt does not have to be placed as quickly as hot mix asphalt (HMA) - as well as the opportunity to place WMA in cooler temperatures. Being able to work in cooler temperatures can allow contractors to pave later in their normal paving season.

The additives, or "technologies," added to WMA reduce the amount of oxidation of the asphalt binder which creates a longer life for the pavement, Smith says. Another benefit is that warm mix asphalt acts like a compaction aid providing improved compaction or density with different mixes, she adds.