Investigation of energy-based interlayer debonding of open-graded friction course pavement under mode I fracture test

Layer bonding performance is essential for ensuring the longevity of open-graded friction course (OGFC) pavements. This study examined the interlayer bonding efficacy between OGFC and the underlying layer, considering variations in underlying layer types and the quantity of tack coat applied. To assess the bonding characteristics, three-point bending tests were performed at temperatures of 0 degrees C and 25 degrees C. Parameters such as bonding stiffness, stress intensity factor, equivalent stress intensity factor, and energy parameters were determined to elucidate the fracture behavior between OGFC layers and their supporting layers. The total fracture energy (GF) was segmented into three components: plastic dissipation energy (Ud), elastic stored energy (Ue), and surface energy (Up), providing a comprehensive analysis of the energy dynamics during fracture. Results showed that at 0 degrees C, the maximum bonding stiffnesses of OGFC-A and OGFC-B were obtained when the coat application contents were 1.0 kg/m2 and 0.5 kg/m2, respectively. With the increase of temperature, the bonding stiffness decreased significantly. At 0 degrees C, the maximum value of KIC of OGFC-A was higher than that of OGFC-B by 7.1 %, which was attributed to the rougher surface of mixture A in terms of texture depth, average roughness and fractal dimension. At 0 degrees C and 25 degrees C, the optimal tack coat application contents for fracture energy were 1.0 kg/m2 and 0.5 kg/m2 for OGFC-A and OGFC-B, respectively. At 0 degrees C, the maximum value of GF of OGFC-B was higher than that of OGFC-A by 54.0 %; while at 25 degrees C, the maximum value of GF of OGFC-B was lower than that of OGFC-A by 16.7 %. At both 0 degrees C and 25 degrees C, the maximum values of Ud + Ue of OGFC-B were larger than that of OGFC-A, indicating that at both 0 degrees C and 25 degrees C, the rougher interface of the underlying layer (mixture A) would not require more energy to initiate a crack. At 0 degrees C, then energy required for crack propagation of OGFC-B was larger than that of OGFC-A; while at 25 degrees C, opposite results were obtained, indicating a rougher interface (mixture A) helped delay the crack propagation. Temperature, underlying layer type, and tack coat affected the proportions of Ud, Ue and Up.