Effect of Short-Term Aging on Low-Temperature Cracking in Asphalt Mixtures Using Mechanical and Thermodynamic Methods

Abstract

One of the most important factors affecting the occurrence of thermal cracking is asphalt binder aging. Many studies have been conducted to identify and prevent this distress. However, the majority of these studies used the results of mechanical tests to evaluate the thermal cracking potential of an asphalt mixture, and little attention has been paid to the main properties of the materials which contribute to the occurrence of thermal cracking. This study investigated the effect of aging on thermal cracking of asphalt mixtures by mechanical and surface free energy (SFE) methods based on the main properties of the material. Eight combinations of asphalt mixtures were prepared using granite and limestone aggregates and two types of asphalt binder, PG 64-16 and PG 58-22. The thermal cracking of asphalt mixtures was evaluated by conducting a mechanical test, i.e., the semicircular bending (SCB) test, at three temperatures; and thermodynamic tests, i.e., sessile drop (SD) and universal sorption device (USD) tests, based on SFE methods. The results of the SCB test indicated that the values of SCB parameters of maximum load, fracture energy, and fracture toughness were higher in the aged asphalt mixtures than in the control mixtures. In addition, the results revealed that aging increased the free energy of cohesion and decreased the free energy of adhesion. This means that, as a result of aging, the probability of thermal cracking decreases in the mastic, whereas the probability of thermal cracking increases due to the weak adhesion between asphalt binder and aggregate. The results of the statistical analysis demonstrated a strong correlation between the free energy of cohesion and adhesion and the parameters of maximum load, fracture energy, and fracture toughness at all three tested temperatures. The coefficients of the regression models presented in this study confirmed the close relationship between the mechanical results and the SFE, suggesting that the thermodynamic methods are effective for investigating low-temperature cracking in asphalt mixtures.