Binder-Grade Bumping and High Binder Content to Improve Performance of RAP-RAS Mixtures : Final Report : SPR 797
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2018-01-01
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Edition:Final Report
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Abstract:General reduction in pavement program funding levels over the past decade and the possible consequent increase in pavement road roughness within the next couple years created a need for low cost yet effective alternative ways to rehabilitate, preserve and maintain roadway network in Oregon. Recycling highway construction materials and minimizing the use of virgin materials can reduce the pavement life cycle costs, improve highway network condition, conserve natural resources, and protect the environment. Although using recycled asphalt pavements (RAP) and recycled asphalt shingles (RAS) is beneficial in many aspects, asphalt pavements with high RAP and RAS contents are more susceptible to cracking. Aged binder in RAP and RAS makes asphalt pavements more brittle and creates long-term durability problems. Using softer virgin binder grade (binder-grade bumping) and higher virgin binder content improve cracking performance of pavements with high amounts of RAP and RAS. However, careful considerations are required in designing asphalt pavements with high RAP and RAS. Softer virgin binder grade and higher binder content make pavements more resistant to cracking, but more susceptible to permanent deformation. Hence, a balance of the combination of RAP and RAS content, binder content, and binder grade should be considered in the mix design. In this study, the performance and cost benefits of using binder-grade bumping and increased binder content strategies in RAP and RAS mixture production in Oregon are quantified. To be able to provide recommendations for asphalt mixture design procedures, blending of binder around RAP is also quantified by using an innovative procedure developed in this study. Laboratory test results were used to develop mechanistic-empirical (ME) pavement models for asphalt mixtures with different RAP and RAS contents. Using the predicted performance from ME models and cost calculations for different combinations of RAP content, binder content, and binder type, life-cycle cost analysis (LCCA) were conducted to determine the performance and cost benefits of using binder-grade bumping and high binder content in Oregon asphalt mixtures. Binder-grade bumping and high binder content strategies recommended in this study are expected to increase the RAP and RAS content in asphalt mixtures, reduce the life-cycle cost, improve the cracking performance, and encourage the widespread use of high RAP/RAS asphalt mixtures in Oregon.
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