摘要
The inclusion of recycled asphalt shingles(RAS)in asphalt mixtures has become increasingly common;however,the underlying design principles vary significantly by agency.The primary objectives of this study included:(1)evaluating the‘binder availability’concept for RAS mixtures through a carefully designed laboratory experiment;(2)demonstrating a balanced mixture performance testing approach for the design of RAS mixtures;and(3)evaluating the field data of RAS mixtures placed in the Midwest region of the U.S.Three asphalt mixture designs with RAS contents of 0,2.5%and 5.0%,which were designed to have nearly identical volumetric characteristics,were investigated.The binder availability was determined to be approximately 100%in the two RAS mixtures considered.In addition,Hamburg wheel tracking and disk-shaped compact tension tests were conducted to evaluate the high-and low-temperature mixture performance.As expected,the addition of RAS significantly improved the rutting resistance.Disk-shaped compact tension(DC(T))test results demonstrated that a soft base binder effectively permitted the design of thermal-crack-resistant RAS mixtures.Field investigations indicated that the performance of pavement surfaces containing RAS was similar to that of surfaces containing only reclaimed asphalt pavement or virgin materials.This study also highlights a performanceengineered mix design approach,which is currently being adopted by several agencies in the Midwest(e.g.,Illinois Toll way,Missouri DOT,etc.)and can provide mix designers a reliable approach for designing innovative asphalt mixtures with higher recycling levels and a modern,heterogeneous composition.Furthermore,the proposed approach may prove to be a simpler,more mixture-centric alternative to the primary method suggested in AASHTO PP78-17,which recommends arbitrary VMA bumping plus binder extraction,recovery,and advanced binder testing.
