Better Roads

March 2014

Better Roads Digital Magazine

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RoadScience 6 March 2014 Better Roads duction, and tests were conducted on the fresh mix, as well as specimens compacted at the plant and after reheating in the research lab," the authors write. "The results showed that the removal of fibers from the OGFC mixtures in both projects did not have any detrimental effects on the mix performance (drain-down, permeability, abrasion resistance, indirect ten- sile strength and fatigue resistance)." The WMA mixture was made with Evotherm modifier and exhibited increased fatigue resistance compared to the control mixture, even though the mix did not contain cellulose fibers, they say. "Additionally, the WMA mixture showed the potential to reduce heat loss due to start-up of the paving operation (i.e., running asphalt mix through a cold material transfer vehicle and then a cold paver)," they say. "Limiting heat loss could improve the consistency of the OGFC mat density from the beginning transverse cold joint, thus potentially enhancing the pavement performance." With care, high-RAP mixes can serve Virginia roads Asphalt mixes containing up to 45-percent reclaimed asphalt pavement (RAP) are viable for the Commonwealth of Vir- ginia, so long as care is taken in production and construction, say Stacey Diefenderfer, Ph.D., P.E., and Harikrishnan Nair, Ph.D., P.E., Virginia Center for Transportation Innovation and Research, Charlottesville, in their paper, Evaluation of High RAP Mixture Production, Construction and Properties. In 2007, the Virginia Department of Transportation (VDOT) introduced specifications to allow RAP percentages of up to 30 percent in asphalt surface mixtures without a change in the virgin binder grade, the authors write, adding since 2007, increasing material costs and a growing awareness of the quantity of RAP available for use have sparked interest in asphalt mixtures having a higher percentage of RAP. Recently, they say, VDOT began to consider allowing the use of surface mixtures with RAP contents of up to 45 percent, and in June 2013, a trial was constructed containing mixtures with 20, 30, 40 and 45 percent RAP for evaluation. The trial indicated higher RAP contents can be tolerated with no loss in performance. "In general, mixtures containing up to 45-percent RAP can be successfully designed, produced and constructed if proper procedures are followed and attention to detail is paid dur- ing design, production and construction," Diefenderfer and Nair say. "In addition, dynamic modulus and flow number test results indicated no significant difference in performance should be expected among the mixtures evaluated, despite slight differences in volumetric properties." They conclude the following: • Based on the dynamic modulus and flow number tests, the 40- and 45-percent RAP mixtures should perform similarly to the 20- and 30-percent RAP mixtures evaluated. • Based on the dynamic modulus and flow number tests, the 30-percent RAP mixture containing a blend of natural and manufactured sand did not behave significantly differently than the 30-percent RAP mixture containing only manu- factured sands. Binder absorption and effective asphalt content were affected by the presence of the natural sand. • The dynamic modulus and flow numbers for the mixture containing 20-percent RAP and PG 70-22 binder were not significantly different than those for the mixtures contain- ing 30-percent RAP and PG 64-22 binder. Binder testing will be performed to verify further the expected perfor- mance of these mixtures. In Kansas, right RAP rectifies road rutting Recycled Superpave mixtures with crushed gravel aggregates and sand significantly improve overall rutting performance compared to the crushed stone or crushed stone/gravel combination in the mix, say Farhana Rahman, Ph.D., Seattle University; Mustaque Hossain, Ph.D., P.E., Kansas State Uni- versity; and Cliff Hobson, P.E., and Greg Schieber, P.E., Kansas Department of Transportation, in their paper, Performance of Superpave Mixtures with High RAP Content in Kansas. Left, hot-mix asphalt (HMA) produced at 320 degrees Fahrenheit produces fumes, while warm-mix asphalt (WMA) at 250 degrees Fahrenheit (right) does not. Photo courtesy of Choubane, Chun, Lee, Upshaw, Greene and Nazef

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