The Effect of Long-Term Aging on Low-Temperature Cracking of Asphalt Concrete Using Mechanical and Thermodynamic Methods

The present study examined the effect of aging on asphalt concrete low-temperature cracking using mechanical test and the surface free energy (SFE) method that is based on the main properties of the material. Twelve combinations of asphalt mixture were prepared using two types of aggregate (limestone and granite), two types of performance-graded asphalt cement (PG 64-16 and PG 58-22), and ultra-high-molecular-weight polyethylene additive (UHMWPE) at 2% of the asphalt cement mass. The low-temperature cracking of asphalt concrete was evaluated by the mechanical semicircular bending (SCB) test at three temperatures, and the thermodynamic tests were performed by determining the SFE components of the asphalt cement and aggregates using the Wilhelmy plate test and the universal sorption device (USD), respectively. The results of the SCB mechanical test indicated that the values of fracture energy and fracture toughness parameters, which are known as an index for determining the sensitivity of asphalt concrete to low-temperature cracking, were lower for aged asphalt concrete than control mixtures. The decrease in asphalt concrete resistance due to aging was more evident in the PG 58-22 asphalt cement than the PG 64-16 asphalt cement. The results of the SFE tests demonstrated that aging increased the non-polar component (between 19.2% and 42.4%) and decreased the acid (between 26.5% and 108.3%) and base (between 6.8% and 10.6%) components of the SFE in asphalt cements. These caused a rise in the free energy of cohesion (between 1.5% and 4.5%) and a reduction in the free energy of adhesion (between 0.3% and 3%), suggesting that the asphalt mixture resistance to failure increased in the mastic, and the resistance to failure decreased at the asphalt cement-aggregate contact surface due to aging. Furthermore, UHMWPE incorporation promoted the cohesion (between 41.0% and 52.1%) and adhesion (between 9.6% and 11.8%) energies of the modified asphalt concrete, thereby reducing the thermal cracking potential of the modified asphalt concrete. Besides, aging had little effect on the SFE components, fracture energy, and fracture toughness parameters of the modified asphalt concrete.