Enhancing the Sustainability and Cost-Effectiveness of High-Modulus Asphalt Concrete Mixes with Crumb Rubber

Asphalt mixes are typically developed using the Superpave mix design method, which focuses on evaluating the volumetric properties of the mix. Current efforts aim to develop asphalt mixes that are performance-based and sustainable. In this context, a French mix design called high-modulus asphalt concrete (HMAC) targets specific performance criteria such as workability, stiffness, resistance to rutting, and fatigue behavior. HMAC utilizes a hard asphalt binder with a high asphalt binder percentage and reduced air voids in comparison to Superpave mixes. In this study, crumb rubber was investigated as a sustainable binder modifier to enhance HMAC performance. All mixes were formulated using locally sourced materials from Louisiana. A total of six asphalt mixes were prepared: one Superpave control mix with PG 76-22 binder without crumb rubber and five HMAC mixes. The HMAC mixes included four crumb-rubber-modified combinations using PG 76-22 and PG 67-22 binders with 10% and 20% crumb rubber, as well as one unmodified HMAC mix with PG 76-22 binder. A fixed RAP content of 20% was used in all mixes. To evaluate the performance characteristics of asphalt mixes, a semicircular bending test was conducted to determine cracking resistance, a dynamic modulus test to assess stiffness, and a flow number test to evaluate resistance to permanent deformation. The results indicated that the HMAC mix prepared with PG 76-22 binder blended with 20% crumb rubber achieved the best overall performance, successfully meeting both the HMAC mix design requirements and Louisiana DOT specifications. The findings demonstrated the feasibility and effectiveness of integrating crumb rubber into high-performance asphalt mixes.