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Road Science: One More Time

RoadScience by Tom Kuennen, Contributing Editor aggregates prone to alkali-silica reactivity (ASR) or is A SPECIAL SERIES The Chemistry of Road Building Materials The Second Time Around Recycled materials need analysis, characterization T here is no stopping the growth of recycled and reclaimed materials in pavements. The use of reclaimed asphalt pavement (RAP), reclaimed asphalt shingles (RAS), recycled concrete aggregate (RCA), and recycled granulated tire rubber (GTR) in pavement mixes and structures is growing dramatically as states accept them more and more in their specs. But because RAP, RCA, RAS and GTR come from a variety of sources, they must be physio-chemically characterized prior to use in mixes. remains after years of exposure to the elements and oxida- 16 September 2012 Better Roads be used as aggregate in fresh asphalt or portland cement mixes, or is it going to be destined for road base, a much shingle feed will come from a supplier that certiﬁes the material meets state specs. The supplier will have sorted, ground and tested the RAS to make sure it does not contain asbestos, wood scraps or metal and is kept separate from pre-consumer (manufacturer waste) shingles (more on this below). Likewise, GTR will come from a supplier that maintains consistency. Thus, physio-chemical analysis of beneﬁciated RAP, RCA, RAS and GTR by in-plant or supplier labs is essential for their continued usage. Because their source composition varies tremendously, these reclaimed materials must be chemically characterized and cataloged; then, blended stockpiles may be managed over time with more or less material added to maintain consistency. Use of RAP and RCA as road base or ﬁll is a less-critical application so a detailed analysis is not essential; here the research emphasis is on the possibility of leached pollutants ﬁnding their way into ground water, and long-term performance. Processing Adds Value to RAP costs the mix producer or contractor additional money, it adds value to the raw materials as they now are consistently sized. raw RAP into at least two sizes, typically a coarse fraction (plus-1/2 or plus-3/8 inch) and a ﬁne fraction (mi- Reclaimed Asphalt Pavement in Asphalt Mixtures: State-of-the-Practice, by Audrey Copeland, formerly materials research engineer technology at the National Asphalt Pavement Association.

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