Investigating of the thermal cracking of asphalt mixtures with surface free energy method, low temperature rheological properties of bitumen, semi circular bending test and aggregate properties

In previous researches, the properties of bitumen and asphalt mixture have been considered for investigation of thermal cracking. In these methods, the roles of different components of the asphalt mixture are not considered. The use of surface free energy and the basic characteristics of asphalt mixture can also be used in the investigation of thermal cracking. In this research, it has been tried to investigate the role of these basic properties of materials in the occurrence of these cracks along with the surface free energy parameters. For this purpose, surface free energy components have been measured for four types of aggregates and eight types of bitumen. Also, the bitumen creep stiffness and m-value were obtained from the bending beam rheometer tests. Asphalt film thickness, aggregate index and the specific surface area of the aggregates have been also determined. For thermal cracking potential, the semicircular bending test was used on 32 different combinations of asphalt mixtures at low temperature. Then, statistical methods have been used for assessing the relationship between the mentioned parameters and the semicircular bending test results. Statistical analysis shows that the basic characteristics of the materials, including the asphalt film thickness, the aggregate index, the free energy of cohesion, the free energy of adhesion, the ratio of basic to acidic components of the surface free energy and the specific surface area of the aggregate have a significant and positive effect on the cracking indices such as semicircular bending fracture energy and fracture toughness.