A novel shearing fracture morphology method to assess the influence of freeze–thaw actions on concrete–granite interface

In cold regions, the bonding strength of concrete–rock interface is considerably influenced by freeze–thaw (F–T) actions. However, accurate approaches to evaluate the influence of F–T cycles on interfacial strength are relatively few. In this study, a novel shearing fracture morphology method for reflecting the influence of F–T cycles on the bonding performances of concrete–rock interface is proposed. A three–dimensional (3D) laser scanning technology is firstly used to determine the interfacial roughness index and joint roughness coefficient (JRC). Thereafter, interfacial debonding tests after subjecting the samples to different F–T cycles (i.e., 0, 10, 20, 30, and 50) are performed using a slant shear test. Based on the measurements obtained by image processing technology (i.e., binarization and 3D reconstruction image observations), a novel shearing fracture morphology approach is proposed to reflect the interfacial morphology features and their residual concrete adhesion area at different F–T cycles. Moreover, the relationships among F–T cycles, interfacial fracture morphology, and shear strength are discussed. The conclusions drawn are as follows: (i) the interfacial bonding strength depends on the roughness and the cementing force between cement and mineral particles of granite; (ii) F–T cycles have a significant effect on the bonding performance of concrete–granite interface caused by the deterioration effects of cementation; (iii) the proportions of concrete adhesion, fracture morphology, and JRCs have positive correlations. This study provides a new approach for evaluating the influence of F–T actions on concrete–rock interfacial debonding features.