Evaluating the moisture damage mechanism in hot-mix asphalt using the fundamental material parameters

Moisture damage in asphalt mixtures is a serious challenge in pavement engineering, affecting the bitumen-aggregate bond and reducing asphalt mixtures’ durability and stability. If it is not controlled, this damage can cause stripping, cracking, rutting, and reduced pavement structural performance, ultimately increasing maintenance and repair costs. Thus, the mechanisms affecting this damage should be accurately understood, and optimal methods should be developed to evaluate asphalt mixtures’ moisture sensitivity. This study evaluated the cohesion of bitumen and the bitumen–aggregate adhesion of various mixtures under dry and wet conditions using a Pull Off device developed by the authors. The surface free energy (SFE) components of aggregate and bitumen were also measured using the Universal Sorption Device (USD) and Wilhelmy Plate (WP) methods, respectively. The Pull Off resistance measured under different conditions was then compared with the parameters derived from the SFE approach. The Pull Off and SFE test results showed that bitumen-aggregate adhesion is influenced by the SFE components of aggregates, and limestone aggregates establish a stronger bond with bitumen due to their alkaline chemical structure. Comparing the data revealed that the type of bitumen plays a key role in cohesion and tensile strength. Softer bitumens had higher non-polar SFE components, which improved cohesion strength, but were more water-sensitive. Therefore, harder bitumens (e.g., PG 70–10) performed better against moisture damage in wet conditions, while softer bitumens (e.g., PG 52–16) demonstrated lower resistance to wet condition failure. The Pull Off and SFE method results demonstrated a strong correlation, indicating that the Pull Off technique can effectively be utilized to investigate the debonding mechanisms of various mixtures under dry and wet conditions. The close alignment of results confirmed the satisfactory accuracy of the custom-designed device.