Impact of high RAP content on the mechanical properties of epoxy-modified asphalt mixtures

Epoxy asphalt pavement shows promise for high-content substitution of reclaimed asphalt pavement (RAP) aggregates. Nevertheless, RAP-related performance degradation requires further validation. This study evaluated how RAP affects the mechanical performance of epoxy asphalt binders and mixtures with different epoxy contents. LSCM and direct tensile tests assessed microstructure and tensile properties, while IDT and 4PB tests examined cracking and fatigue resistance. Based on the results, an optimal epoxy content and RAP incorporation strategy are recommended. The results indicate that aged asphalt exacerbates the variability of the particle size distribution in ERA fluorescence images and compromises the elongation rate of the ERA binder. With 60% RAP aggregates substitution, epoxy asphalt mixtures with 30% and 40% epoxy contents demonstrate fatigue endurance limits higher than 190 με, which can easily withstand the field tensile strain levels of 70–150 με. 60% RAP aggregates substitution only leads to a 10%–30% decline in the cracking and fatigue performance of epoxy asphalt mixture at 20% and 30% epoxy contents. Epoxy asphalt pavement with 30% epoxy content (typically used in high-priority expressways) is recommended for RAP aggregates incorporation, as it better balances the economic benefits of RAP aggregates with its superior performance.