Evaluation of Millability and Recyclability of Asphalt with Paving Interlayers

Reclaimed asphalt pavement (RAP) has been widely incorporated into roadway base and surface courses, as they provide economic and environmental benefits that lead to sustainable construction practices. However, because of the increasing use of paving interlayers (e.g., geotextiles, geogrids, and geocomposites) during roadway rehabilitation, the likelihood of milling projects involving asphalt layers with paving interlayers (referred to as GRAP) has significantly increased. Consequently, the assessment of potential GRAP reuse in geotechnical and pavement applications becomes essential. This research study aims at evaluating the millability and recyclability of asphalt layers with paving interlayers. Specifically, sections with and without paving interlayers were first milled to evaluate the millability of asphalt layers with paving interlayers. Subsequently, the recyclability of GRAP for the base and surface course of pavements was assessed by quantifying the geotechnical characteristics of millings collected from asphalt layers with paving interlayers, referred herein as geosynthetic RAP or GRAP, and those without paving interlayers (RAP). The evaluation of RAP and GRAP materials for road base suitability included blending them with virgin aggregates and investigating these blends via determination of particle size distribution, binder content, compaction characteristics, abrasion resistance, hydraulic conductivity, and resilient modulus. The evaluation of RAP and GRAP materials for surface course suitability involved preparing asphalt mixtures that incorporated RAP and GRAP and quantifying their particle size distribution, indirect tensile strength, and moisture susceptibility. Comparison of the results obtained from five different base course blends and five different asphalt mixtures demonstrated that the base course blends and asphalt mixtures with GRAP exhibited properties similar to those with RAP. Also, the results of this investigation indicate that asphalt mixtures (surface course) and granular base courses can incorporate up to 30 % and 50 % GRAP, respectively, thus leading to sustainable roadway construction practices.