Developing the thermodynamic-mechanical parameters for evaluating the bonding potential and moisture sensitivity of polymer-modified asphalt binders

Although thermodynamic and mechanical methods are commonly used to evaluate cohesion and adhesion bonds of asphalt materials, they each have limitations in representing actual field performance, especially for modified binders. This study investigates the influence of varying SBS contents (0–7 %) on the bonding performance and moisture resistance of asphalt binders in combination with limestone and granite aggregates. An experimental program was designed that included Fourier Transform Infrared (FTIR) spectroscopy, SARA fraction, softening point and penetration tests, contact angle measurements, SFE (thermodynamic) approach, and the BBS test (mechanical approach). The results of BBS test were used to determine the bond strength and quantifying the failure surfaces to the adhesive and cohesive failure percentages. New combined thermodynamic–mechanical parameters were developed under dry and wet conditions and were validated using mixture performance tests such as indirect tensile strength ( ITS ) and tensile strength ratio ( TSR% ). The findings showed that increasing SBS content changed the binder structure by increasing asphaltenes and reducing maltenes, which improved stiffness, cohesion, adhesion, and overall bond strength. However, binders with less than 3 % SBS showed poor polymer distribution and incomplete network formation, leading to weaker bonding. Higher SBS contents also reduced binder wettability, which increased adhesive failure under both dry and wet conditions. Additionally, SBS improved moisture resistance for limestone aggregates but made granite mixtures more sensitive to moisture, showing that binder–aggregate compatibility plays a key role. Direct measurement of the contact angle was found to be a more reliable method for evaluating binder wettability than the spreading coefficient, a thermodynamic parameter. In general, the proposed thermodynamic–mechanical parameters ( EP dry and EP wet ) showed strong correlations with mixture performance results ( ITS dry and TSR% ), suggesting that combining thermodynamic and mechanical properties can predict asphalt mixture performance more accurately than using either approach alone, particularly more accurate than thermodynamic parameters.