Investigation on Asphalt–Aggregate Interfacial Adhesion Under Hygrothermal Conditions Using Molecular Simulation

As a typical multiphase composite material, the asphalt mixture possesses an inherently weak zone at the asphalt–aggregate interface. This weak zone is especially vulnerable under hygrothermal conditions, where moisture and temperature jointly accelerate interfacial deterioration. In this study, molecular models of the asphalt–aggregate interface were constructed under both dry and wet conditions. The effects of aggregate type, temperature, and moisture, as well as their coupling effects, on interfacial adhesion performance were systematically investigated. The results indicated that the adhesion of asphalt binder to the three representative aggregate components decreased in the order of CaO, Al2O3, and SiO2. Within the temperature range of 5 °C to 65 °C, the adhesion work exhibited a non-monotonic trend, initially increased and then decreased, with a peak at 25 °C. Water molecules competitively adsorbed onto the aggregate surface upon entering the interface, hindering effective contact between asphalt molecules and aggregates. CaO showed the highest sensitivity to moisture, posing a high risk of moisture damage. Aggregate composition dominated interfacial adhesion, followed by moisture and then temperature. Moisture undermined adhesion by disrupting the interface contact, whereas temperature exerted a modulating effect that was more pronounced for SiO2 and Al2O3 at elevated temperatures, while CaO remained highly moisture-sensitive regardless of temperature. The coupled moisture–temperature effect further exacerbated interfacial failure, with high-temperature and high-humidity conditions causing the most significant damage to interfacial stability. This study reveals the adhesion performance and underlying mechanisms at the asphalt–aggregate interface from a microscopic perspective, clarifies the influence patterns and contribution weights of various factors, and thus provides a theoretical basis for optimizing the interfacial adhesion performance of asphalt mixtures.