Effect of long-term aging on low-temperature cracking of asphalt mixtures using mechanical and thermodynamic methods

In most existing studies to investigate the aging performance of asphalt mixes, the results of mechanical tests are used to investigate the thermal cracking potential of an asphalt mix and less attention is paid to the basic properties of materials that are important in the event of this cracking. Accordingly, the present study investigates the effect of aging on thermal cracking of 12 different compositions of asphalt mixtures through mechanical methods and free surface energy (SFE), which is based on the main properties of the material. Thermal cracking of asphalt mixtures has been evaluated by performing semi-circular bending mechanical tests and thermodynamic tests by determining the SFE components of bitumen and aggregates. The results showed that the parameters of fracture energy and fracture toughness, which are known as indicators of sensitivity of asphalt mix to thermal cracking, for aged asphalt mixtures between 6.3-13.7% and between 6.5-10.7%, respectively. The results of SFE tests show that aging causes an increase in the non-polar component between 1.3-1.5% and a decrease in the acidic and basic free energy components of bitumen between 41.1-53.4% and between 334.2-349.6%, respectively. These results have increased the amount of free cohesive energy from 0.63 to 1.03 (ergs/cm2). Also, aging reduces the free energy of bitumen-aggregate adhesion with a maximum reduction of 2.61 (ergs/cm2). This means that aging reduces the coverability of bitumen on the aggregate surface and the resistance to fracture at the bitumen-aggregate interface.