Effects of interface roughness and interface adhesion on new-to-old concrete bonding

Abstract

Concrete interfacial roughness plays a great role in contributing to the new-to-old concrete bonding. In this research, artificial roughness was created on the surface of 180-day concrete with iron combs of different-shaped saw-teeth; the morphology data of concrete interface was captured using self-created analysis equipment of laser triangulation ranging; then the morphology data was processed and reconstructed into an interface in three dimensional form with MATLAB software; the fractal dimension of the three-dimensional reconstruction interface was calculated based on the above reconstruction. Mechanical properties of new-to-old concrete bond were tested. The influence of interface roughness on new-to-old concrete bond was studied. The effects of interface adhesion agents on new-to-old concrete bond were also studied. Results show that the concrete interfacial fractal dimension is in good relevance with new-to-old concrete mechanical properties, including splitting tensile strength, flexural strength and bonding strength. If concrete interfacial fractal dimension is higher, new-to-old concrete can obtain higher mechanical strengths. The interface adhesion agents greatly improve the mechanical strength of new-to-old concrete, and result in higher bonding strengths. Different kinds of adhesion agents may have different effectiveness, and they may contribute to a different degree of increase in mechanical strength. The three zone-two layer model was established to explain the mechanism of new-to-old concrete bonding, which indicates that the transition zone between old and new concrete is the key region of the new-to-old concrete bonding. While the interfacial roughness affects the permeable layer and the interface adhesion agents improves the reaction layer, the transition zone between old and new concrete is properly improved, which contributes to a better new-to-old concrete bonding.