Fracture and Thermodynamic Properties of Calcined Dolomite-Modified Asphalt Mixtures under Acidic and Alkaline Moisture Conditions at Low Temperatures

Enhancing asphalt pavement durability against environmental stressors—particularly moisture-induced damage—is critical for infrastructure longevity. This study investigates the low-temperature fracture properties of modified hot-mix asphalt (HMA) with calcined dolomite under acidic (pH=5, pH=6), alkaline (pH=8, pH=9), and neutral (pH=9) moisture conditions. Additionally, the rheological and thermodynamic properties of the modified bitumen were characterized. The combined results provide insight into the mechanism of the modifier’s effect from mechanical, adhesion, and rheological perspectives under these wet conditions. Calcined dolomite was blended with the base bitumens at 0.5% and 1% by weight. HMAs under acidic/alkaline wet conditions exhibited lower fracture energy (FE), fracture toughness (FT), and bitumen-aggregate adhesion. However, calcined dolomite used at two weight percentages of 0.5% and 1% significantly increased the bitumen-aggregate adhesion and FE/FT of HMAs under acidic/alkaline moisture conditions. Thus, calcined dolomite increased the energy required for the formation or propagation of low-temperature cracks at the bitumen-aggregate interface or in the bituminous mastic by increasing the bitumen-aggregate adhesion and reducing the tendency of bitumen and aggregate to form bonds (ionic and covalent) with acidic/alkaline waters. The results of the rheological tests on bitumen at low temperatures were consistent with the mechanical and thermodynamic test findings, demonstrating that calcined dolomite increased the m-value of bitumen under the influence of acidic/alkaline water. Statistical analysis of the findings also indicated that 1% calcined dolomite (by bitumen weight) had the most significant effect on improving HMA’s thermodynamic and mechanical properties under various moisture conditions.