Effects of crosslinking density on properties of crumb rubber/SBS composite modified asphalt: Insights into microstructure evolution and property correlation

Crumb rubber modified asphalt offers a sustainable route for recycling waste tires, but its micro–macro performance relationships remain poorly understood. In particular, quantitative links between microstructural descriptors and macroscopic properties have not been clearly established. This study aims to clarify how crosslinking density governs the thermal, morphological, and rheological performance of crumb rubber/SBS composite modified asphalt (CRCMA). To this end, experimental characterization was integrated with molecular dynamics simulations. This study links microstructural indicators such as solubility parameter and interaction energy to macroscopic behavior through a novel metric termed the Effective Dosage Ratio (EDR). This metric provides a quantitative index derived from experimental data to evaluate the efficiency of property improvements. Results reveal that moderate crosslinking density achieves superior comprehensive properties, enhancing rutting resistance, improving low-temperature flexibility, and markedly increasing storage stability. Notably, the storage stability EDR was 2.6 times higher than that of low-crosslinking samples. These improvements are attributed to an optimized solubility parameter that indicates thermodynamic compatibility closest to the base asphalt, a moderate cohesive energy density, and balanced interfacial binding energy. By introducing EDR as a quantitative bridge between microstructure and macro-scale behavior, this work establishes a framework for cross-dimensional comparison of CRCMA performance. The findings provide mechanistic insights into structure–property relationships and propose a performance-driven design strategy for CRCMA, supporting waste tire valorization, reducing energy use and emissions, and advancing sustainable pavement engineering.