Influence of surface roughness and hydrophilicity on bonding strength of concrete-rock interface

The good bonding in a concrete-rock interface is an important premise to perform the supporting functions of concrete and shotcrete. However, the bonding strength of a concrete-rock interface is influenced by many factors such as rock mineral composition and textural features, surface roughness, interface treatments, and concrete mixture and its casting technique. In this study, we focused on the effects of surface roughness and hydrophilicity on the bonding performances of concrete-granite interface. First, we expressed these two interfacial parameters (i.e., joint roughness coefficient (JRC) and contact angle (CA)) quantitatively using fine measurement methods. Subsequently, after the concrete-granite composites were prepared, a series of interfacial slant shearing experiments of concrete-granite composites were performed for different JRC and CA values. Finally, the relationship between bonding strength and interfacial features were discussed, and a two-element interfacial shear model for the concrete-rock composite was proposed based on the experimental tests and theoretical derivation. Three primary outcomes are as follows: (1) the bonding strength always increases with the JRC, whether the interface is hydrophilic or hydrophobic. Simultaneously, the bonding strengths of hydrophilic interfaces are relatively better than those of hydrophobic interfaces for the same JRC value. (2) A coupling effect between surface roughness and hydrophilicity should exist on the bonding strength of the concrete-rock interface. In particular, the more severe the interfacial roughness, the weaker is the influence of hydrophilicity on the bonding strength. (3) It is significant to comprehensively consider the effects of surface features and the adhesion of concrete to reflect the bonding strength of the concrete-granite composite. The results of the proposed model considering these properties are in good agreement with the experimental values. This work provides a reference for understanding the bonding strength changes in concrete-rock interface owing to the effects of interfacial properties. (C) 2019 Elsevier Ltd. All rights reserved.