Balancing Cracking and Rutting Resistance in RAP Asphalt Mixtures: Practical Testing Approaches for Resource-limited Conditions

Introduction In many emerging economies, highways constitute the main transportation infrastructure. However, a significant portion of the paved network remains in fair-to-poor condition and requires rehabilitation. Pavement milling is widely used for this purpose, generating Reclaimed Asphalt Pavement (RAP). Although RAP recycling offers economic and environmental benefits, especially in resource-limited contexts, Hot Mix Asphalt (HMA) designs based solely on volumetric parameters do not ensure adequate resistance to fatigue cracking and permanent deformation, and advanced dynamic testing methods are often unavailable. This study evaluates the potential of the High-Temperature Indirect Tensile (HT-IDT) and indirect tensile asphalt cracking (IDEAL-CT) tests on Marshall specimens to optimize binder content in asphalt mixtures with and without RAP, focusing on two heavily trafficked rural highways in Brazil. Methods The HT-IDT and IDEAL-CT tests were applied to Marshall-compacted specimens at varying binder contents (4%, 5%, and 6%), with and without RAP as a partial replacement for coarse aggregates, enabling the application of the Balanced Mix Design (BMD) concept. Results The Marshall method tends to produce mixtures with higher binder contents, improving cracking resistance but reducing rutting performance. Binder content optimization improved rutting resistance by up to 51% for RAP mixtures and 22% for reference mixtures without compromising cracking resistance. CT Index at the design binder content (165 and 182 for mixtures without and with RAP, respectively) significantly exceeded the minimum threshold of 100 recommended for heavy-traffic conditions. Discussion These findings suggest that conventional volumetric mix design methods may fail to provide durable solutions for highways subjected to high temperatures and heavy loads. The use of RAP as a partial replacement for coarse aggregates proved technically feasible, with mechanical behavior comparable to or better than that of the reference mixture. Conclusion The integrated use of HT-IDT and IDEAL-CT tests on Marshall specimens provides a practical and accessible framework for implementing the BMD concept in resource-limited laboratory environments, demonstrating that volumetric criteria alone are insufficient to ensure adequate pavement performance under heavy traffic and high-temperature conditions.