Warm-mix asphalt (WMA) and recycled materials in asphalt (RAP) are the hot ticket on road projects, according to results of a survey by the National Asphalt Pavement Association under contract to the Federal Highway Administration. A survey of 1,141 U.S. asphalt plants found that they produced about 86.7 million tons of WMA during 2012 construction—almost a quarter of all asphalt mixes. This marks a 416% increase since a 2009 survey.
Conducted in mid-2013 and released on Jan. 29, the study also found that about 68.3 million tons of RAP and 1.86 million tons of recycled asphalt shingles (RAS) were used in new mixes in the U.S. in 2012. The amount of RAP and RAS used by producers exceeded the amount collected.
WMA and RAP began to take hold within the past decade (ENR 3/30/09 p. 15). WMA needs less energy to produce, reduces emissions, improves worker safety and offers construction benefits. U.S. Secretary of Transportation Anthony Foxx frequently remarks that WMA alone is expected to save $3.6 billion in energy costs by 2020. The use of RAP and RAS during the 2012 paving season translates to a savings of 21.2 million barrels of liquid-asphalt binder, saving taxpayers some $2.2 billion, says NAPA.
Also last month, Astec Inc. announced it sold its 600th proprietary warm-mix system since it began producing it in 2007. In the Astec system, water is injected into the mix with liquid-asphalt cement, in lieu of additives. Water causes the liquid asphalt to foam and expand in volume and then coats the aggregate at a lower temperature, says Mike Varner, Astec chief engineer.
"There's been incredible growth," Varner says, noting that the foaming concept originated in the 1950s at the University of Iowa, with further research by Australia's Mobil Oil. Unlike costly commercial additives, water injections don't require the basic mix to be redesigned for them, he says.