Adhesion of repair systems to concrete: influence of interfacial topography and transport phenomena

Eight types of cement slurries were applied to concrete substrates. Surface preparation involved mechanical action – sandblasting and polishing – as well as saturation regulation, both dry and saturated surface wet. The adhesion strength for the different combinations was measured by direct tensile tests. Multivariate statistical analysis led to the identification of a major effect of surface saturation on the results. Knowledge of the interfacial behaviour was obtained by the discrimination of the effects of partial interaction between slurry and aggregates and slurry and cement mortar, respectively. It clearly showed that a third factor has to be taken into account in the explanation of adhesion, namely the interfacial transition zone between cement paste and aggregates, due to its porosity and anchoring effect. This effect was quantified by topographical observation and image analysis. Penetration of cement slurry was also confirmed by observation with binocular and fluorescent microscopy.