Experimental study on Geotechnical and Mechanical Performance of Reclaimed Asphalt Pavement (RAP) utilization in Cement-Treated Base (CTRB)

Abstract

The increasing demand for sustainable pavement materials has prompted growing interest in Reclaimed Asphalt Pavement (RAP) as a substitute for virgin aggregates in Cement-Treated Recycled Base (CTRB) construction. Despite existing studies on RAP utilization, the integrated mechanisms governing density formation, cement bonding efficiency, and strength development in CTRB mixtures remain insufficiently understood. This study investigates the mechanical and compaction behavior of CTRB mixtures composed of six RAP–virgin aggregate (Base A) proportions, each stabilized with 5% Portland Composite Cement. Laboratory testing included Modified Proctor compaction, California Bearing Ratio (CBR), and Unconfined Compressive Strength (UCS) at 7, 14, and 28 days of curing. Finite Element Method (FEM) analysis using LUSAS software was also performed on the optimum composition to evaluate the stress, strain, and displacement responses under compressive loading. Results indicate that mixtures containing 50–70% RAP yield superior mechanical performance, with the BA50–R50 mixture achieving the highest 28-day UCS of 1.380 MPa and the BA70–R30 mixture recording the highest CBR of 275%. A key novel finding is the inverse CBR–UCS relationship observed across compositions: residual asphalt in RAP enhances cement matrix bonding and compressive strength, yet does not proportionally improve CBR, which is governed more strongly by aggregate density and gradation. FEM results confirmed linear-elastic behavior, with a maximum displacement of 0.0148 mm and microstrain levels, demonstrating the structural stiffness of the optimum mixture. These findings provide new mechanistic insight into RAP–cement synergy and offer practical guidance for designing sustainable, high-performance pavement base layers.