Crack Resistance Evaluation for In-Service Asphalt Pavements by Using SCB Tests of Layer-Core Samples

Transverse cracking is one of the major distresses of asphalt pavements with a semirigid base. After subjected to the loading, aging, and other factors, the materials properties of in-service asphalt pavements are quite different from the initial properties, so it is important to directly use the layer core samples to evaluate the crack resistance for the in-service pavements. In this paper, five expressways were selected, and 195 core samples were obtained from the different asphalt layers in 13 road sections. The field transverse cracking survey results show that almost 80% transverse cracks are bottom-up transverse reflective cracking. The semicircular bending (SCB) tests were performed on the layer core samples, and analysis of variance (ANOVA) analysis was applied to reveal the sensitivities of tensile strength and fracture energy to equivalent single axle load (ESAL), service age, aggregate gradation, air voids, and specimen location. The results of the ANOVA analysis indicate that ESAL and service age significantly affect tensile strength of surface and middle asphalt layers, and fracture energy of surface and middle asphalt layers are sensitive to aggregate gradation and service age. ESAL only acts on the upper two asphalt layers, not the bottom asphalt layer, and SCB test results of the bottom asphalt layer are only sensitive to air voids. Then the field investigation of pavement transverse cracks were launched, and the results present that there are three stages of process for transverse cracking development, including (1) crack initiation stage, which occurs during the first few in-service years, (2) crack explosive growth stage, in which the total length of transverse cracks sharply rises, and (3) crack stabilization stage, in which the total length of transverse cracks tends to be stable with a much slower growth speed than the second stage. The critical service age point between the latter two stages could be considered as the appropriate maintenance time for transverse reflective cracking. Furthermore, the correlation analyses were conducted between laboratory SCB test results and field cracks investigation. The results show that field transverse cracks performance have a better correlation relationship with fracture energy of the core samples, and a limit fracture energy value of $\mathrm{2,500}\mathrm{J}/{\mathrm{m}}^2$ is proposed to prevent reflective cracking in this study.