Effects of calcined dolomite on the fatigue performance of asphalt concrete affected by water with variable acidity
Mehdi Mehdinazar, Gholam Hossein Hamedi, Amir Hossein Asadi
Abstract
Surface contaminants on pavements, combined with road runoff, can alter the pH of water infiltrating the asphalt concrete (AC), which weakens the mixture's resistance to failures such as fatigue cracking. To address this, we evaluated the potential of calcined dolomite powder for enhancing moisture resistance in asphalt mixtures by adding it to bitumen at 0.5% and 1% by weight. We conducted tests across varying pH levels (5-9) using two bitumen grades (PG 58-22, PG 64-16) and two aggregate types (limestone and granite). We assessed mechanical performance with the dynamic shear rheometer and semi-circular bending tests, and analyzed thermodynamic behavior using surface free energy theory through the Wilhelmy Plate and Universal Sorption Device methods to study adhesion and cohesion between materials. Acidic and basic moisture conditions-particularly acidic-reduced the adhesion of the bitumen-aggregate system by decreasing their debonding energy by 30% across various pH levels. This weakened adhesion increased the likelihood of fatigue crack formation at the bitumen-aggregate interface. In contrast, calcined dolomite improved bitumen-aggregate adhesion in both acidic/basic environments. Statistical analysis further demonstrated that increasing the calcined dolomite content from 0.5 to 1% significantly reduced the negative effect of acidic and basic waters on bitumen-aggregate adhesion. Mechanical testing methods also corroborated the thermodynamic evaluation. Specifically, calcined dolomite significantly enhanced fracture energy and fracture toughness of the AC, and the bitumen's fatigue parameter under various moisture conditions. Calcined dolomite enhances both adhesive strength of the bitumen-aggregate and the bitumen's cohesive strength by modifying bitumen's polar and non-polar properties, ultimately increasing the mechanical resistance of both bitumen and AC against fatigue-induced cracking through both adhesive and cohesive failure mechanisms.