Assessing Low-Temperature Cracking in Asphalt Mixtures through Mix Design and Thermodynamic Parameters

Traditional tests for low-temperature cracking mainly focus on bitumen or overall mixture properties, overlooking the contribution of asphalt mixture elements. This study investigated the fundamental material properties influencing low-temperature cracking by considering mix design and surface free energy (SFE) parameters. The SFE elements of four aggregate types and eight bitumen types were measured using the universal sorption device and Wilhelmy plate methods, respectively. Based on these measurements, important SFE parameters such as cohesion free energy (CFE), adhesion free energy (AFE), and the ratio between base and acid elements (RBA) in the aggregate SFE were calculated utilizing bitumen and aggregate SFE data. Additionally, material parameters, including the bitumen's creep stiffness (CS) and CS diagram slope (m-value), were determined through bending beam rheometer tests. Further, factors related to the mix design, such as the aggregates' specific surface area (SSA), bitumen film thickness (BFT) on aggregate surfaces, and aggregate index (Ia), were examined. A semicircular bending (SCB) test was conducted on 32 fabricated asphalt mixtures to assess the correlation between these parameters and their impact on low-temperature cracking potential in the asphalt mixtures. Multiple linear regressions were employed to predict the objective functions. The statistical analysis demonstrated that SFE concepts can effectively determine the potential for low-temperature cracking in asphalt mixtures. According to SCB test results concerning fracture toughness and fracture energy, our proposed models indicated the significantly positive influence of factors such as BFT, Ia, AFE, CFE, SSA, and RBA.