Better Roads Digital Magazine
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injected into RAP or aggregate in a mixing chamber, either in a self-propelled recycling machine, or portable plant. In this cold-mix foamed asphalt process, the recycled aggregate is not completely coated, as is the process with in-plant foamed injection using mostly virgin aggregate. Instead, as 100 percent reclaimed materials are intro- duced to the pug mill, foamed asphalt is injected into the material stream, and acts as a binding agent to "glue" the reclaimed aggregates together. This will permit use of less liquid asphalt and much lower mixing temperatures. With 100 percent of exist- ing aggregates used in cold recycling, 2.2 to 2.5 percent liquid asphalt is used to partially coat the RAP and any added virgin aggregate, opposed to in-plant foamed technologies that completely coat the aggregate – as is needed for critical applications like friction courses – that use 5 percent liquid asphalt. Moisture Sensitivity Enhanced? At the 2nd International Warm-Mix Conference in Oc- tober, presentations heralded the spread of WMA from coast to coast. For example, NAPA director of engineering Kent R. Hansen, P.E., reported that WMA use was growing very rapidly, with a 148-percent increase in use from 2009 to 2010, the most recent year for which firm data were available, rising from 19.2 million tons to 46.7 mil- lion tons in one year. That's drawn from estimated total volume of both HMA and WMA of 358 million tons in 2009 to 360 million tons in 2010. Download the report by Googling NAPA Information Series 138. As usage grows, WMA has moved from a boutique product to the mainstream, and is coming under in- creased scrutiny, with the question being raised of whether the physiochemistry of warm mixes makes them more sensitive to moisture damage. Moisture damage is a well-recognized phenomenon, reports The Asphalt Institute in its 2007 pamphlet, Mois- ture Sensitivity: Best Practices to Minimize Moisture Sensitivity in Asphalt Mixtures, with 10 of 50 states reporting fresh hot mixes being treated for moisture damage. Because in the absence of an emulsifier oil and water Smooth as glass. topconpositioning.com/mmgps-paving It's time. Write 114 on Reader Service Card or visit www.betterroads.com/info Topcon_BR0812.indd 1 1208_BR_MMGPS_reflection.indd 1 Better Roads August 2012 23 7/18/12 10:28 AM7/24/12 9:52 AM