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In recent years, there has been increased interest in the use of reclaimed material in asphalt mixtures. The use of recycled asphalt shingles (RAS) has been of interest because of the high asphalt content, although this asphalt is considerably stiffer than that typically used in paving mixtures. The Virginia Department of Transportation has specifications allowing the use of post-manufacturing waste and post-consumer RAS, although use has been limited. In addition, the specifications do not provide for the use of RAS in stone matrix asphalt (SMA). In response to producer requests for RAS use in SMA, this study investigated the use of RAS in SMA mixtures in VDOTs Salem and Staunton districts. Mixtures were sampled during production, characterized, and evaluated using a suite of laboratory tests including dynamic modulus, flow number, rut depth, and bending beam fatigue. Test results indicated that, as expected, the inclusion of RAS appears to improve high temperature / low frequency modulus values and rutting resistance. The inclusion of RAS had mixed effects on the mixture performance in laboratory fatigue testing. Binder testing on one set of mixtures indicated that the virgin binder grade may significantly affect the degree of blending of the RAS binder. In addition, extracted binder Tc values indicated that the inclusion of either RAP or RAS may have adverse impacts on cracking susceptibility. These findings should be validated with field performance and additional mixtures. The study recommends that the Virginia Department of Transportation not change specifications to allow RAS in SMA at this time. In specific situations, the use of RAS in SMA should be approached judiciously, as when effectively located and properly designed, produced, and placed. RAS mixtures have the potential for improved rutting performance, although impacts on cracking performance must be carefully assessed.
In the years since the development and subsequent success of Stone Matrix Asphalt (SMA), a plethora of articles have emerged, scattered throughout various publications. The time is right for a comprehensive resource that collects, examines, and organizes this information and makes it easily accessible. A compilation and distillation of the latest k
Part 1: Summary of research results; Part 2: Mixture design method, construction guidelines, and quality control/quality assurance procedures
TRB's National Cooperative Highway Research Program (NCHRP) Report 752: Improved Mix Design, Evaluation, and Materials Management Practices for Hot Mix Asphalt with High Reclaimed Asphalt Pavement Content describes proposed revisions to the American Association of State Highway and Transportation Officials (AASHTO) R 35, Superpave Volumetric Design for Hot Mix Asphalt, and AASHTO M 323, Superpave Volumetric Mix Design, to accommodate the design of asphalt mixtures with high reclaimed asphalt pavement contents.
The Indiana Department of Transportation has successfully used Reclaimed Asphalt Pavement (RAP) for decades because of its economic and environmental benefits. Because of uncertainties regarding the types of aggregates contained in RAP and their resulting frictional properties, INDOT has until recently disallowed the use of RAP in asphalt surface mixtures. In addition, the hardened asphalt binder in the RAP could potentially increase the occurrence of thermal cracking. This research was conducted to explore the effects on RAP with poor or unknown aggregate qualities to establish maximum allowable RAP contents to provide adequate friction. The effects of RAP on thermal cracking were then investigated at the potential allowable RAP contents. Laboratory testing showed that the addition of poor quality RAP materials did impact the frictional properties and cracking resistance of the mixtures, but that lower amounts of RAP had little effect. The frictional performance of the laboratory fabricated and field sampled RAP materials was acceptable at contents of 25% but may be questionable at 40%. Field friction testing was also conducted on existing roadways with RAP to explore their field frictional performance. Several low volume roadways and one experimental interstate project were tested. The field results showed acceptable performance after 3 to 5 years of low volume traffic at RAP contents of 15-25% and after more than 10 years of interstate traffic with 15% RAP. Low temperature testing showed an increased susceptibility to thermal cracking as the RAP content increased but the change in critical cracking temperature was relatively small at the 25% RAP level. At 40% RAP without a change in the virgin binder grade, the critical cracking temperature was about 6 C warmer than the control mixture. This finding supports the need for a binder grade change for RAP contents greater than 25%, as indicated in other research and as required by the current INDOT specifications.
"More than 90 percent of highways and roads in the United States are built using hot-mix asphalt (HMA) or warm-mix asphalt (WMA) mixtures, and these mixtures now recycle more than 99 percent of some 76.2 million tons of reclaimed asphalt pavement (RAP) and about 1 million tons of recycled asphalt shingles (RAS) each year. Cost savings in 2017 totaled approximately $2.2 billion with these recycled materials replacing virgin materials. The TRB National Cooperative Highway Research Program's NCHRP Research Report 927: Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios presents an evaluation of how commercially available recycling agents affect the performance of asphalt mixtures incorporating RAP and RAS at high recycled binder ratios."--