Understanding the moisture sensitivity of warm mix asphalt binders based on bond strength

Moisture damage in asphalt mixtures is typically attributed to the loss of bond strength at the interface of the asphalt binder and aggregate matrix. Therefore, selecting an appropriate combination of materials that resist moisture-induced damage is critical. This concern is of utmost importance when asphalt mixtures are prepared at lower production temperatures, i.e., warm mix asphalt (WMA) mixtures. This paper attempts to quantify the impact of moisture on asphalt mixtures prepared using four different warm mix additives and two aggregates through a bond strength (BS) test. Results showed that WMA binders impart similar or even higher BS than base asphalt binder, regardless of aggregate source and moisture exposure (wet or dry). Moisture sensitivity, evaluated through bond strength ratio (BSR), indicated that the application of WMA additives improves the moisture sensitivity, despite lower production temperatures, compared to the base asphalt binder. Statistical analysis showed that asphalt binder type significantly affects the bonding mechanism and moisture sensitivity. Based on the ranking protocol used in this study, it can be stated that the application of Rediset, a chemical-based WMA additive, unveils the best performance among other WMA additives in VG30, which is the most commonly used asphalt binder for paving applications.