A novel roughness parameter for more precise estimation of the shear strength of concrete-to-concrete interfaces

Abstract

Concrete-to-concrete interfaces are common in new reinforced concrete structures with different casting stages and or with precast members with cast-in-place parts, as well as in rehabilitation of existing reinforced concrete structures. Their longitudinal shear strength has been studied in the last five decades. Today, it is established that this is ensured by a combination of adhesion, aggregate interlock, friction, and dowel action. Being all these resistant mechanisms, but mainly friction, highly dependent on the surface roughness, the quantification of the latter is of paramount importance.This paper investigates the correlation between the friction coefficient and the surface roughness of concrete-to-concrete interfaces. An experimental campaign of direct shear tests, performed on specimens with different surface treatments (smooth, rough and corrugated), was carried out. The surface’s texture was analysed using a 2D Laser Scan and different roughness parameters (extreme, mean and segments) were calculated, then correlated with the corresponding shear strength and, lastly, based on the latter, correlated with the friction coefficient.Results showed that the extreme roughness parameters, as well as the peaks’ height related parameters, have poor or no correlation with the magnitude of the friction coefficient. The average roughness of the profile, its mean square, the mean valley depth, and the mean peak-to-valley height turned out to have the strongest positive correlation with the friction coefficient. Based on these, a novel combined roughness parameter with an optimized correlation with the friction coefficient was derived and proposed.