Availability adjusted mix design method as a tool to mitigate the adverse effects of RAP on the performance of asphalt mixtures

Abstract

The use of high percentages of reclaimed asphalt pavement (RAP) in asphalt mixtures offers economic and environmental advantages. However, state agencies place limits on RAP usage to avoid its indiscriminate use without a full understanding of its long-term performance implications. To achieve a more informed and rational use of higher RAP contents, it is essential to quantify recycled binder availability (RBA) and incorporate it into asphalt mixture design. The current design methods often assume complete RBA, leading to less durable mixtures. Standardized mixture design methods fail to rigorously account for the effects of RBA on the volumetric composition of asphalt mixture. Recently, the availability adjusted mixture design (AAMD) method was developed to address these issues by explicitly considering partial RBA in the interpretation of mixture volumetric properties and accounting for the role of RAP agglomerations on aggregate structure. This study tests the hypothesis that the AAMD method can mitigate the adverse performance consequences of RAP through the control of ‘available’ volumetric and effective binder properties. This was achieved by comparing virgin and RAP mixtures designed with similar ‘available’ volumetric properties according to the AAMD method. Additionally, control mixtures with RAP contents ranging from 20 to 35 percent were compared to AAMD mixtures with similar ‘available’ volumetric properties designed with the same RAP content and with 50 percent RAP. The collective results demonstrate that the AAMD method effectively mitigates negative performance consequences of RAP by controlling the ‘available’ volumetric and effective binder properties.