Bond strength between concrete and repair mortar and its relation with concrete removal techniques and substrate composition

Abstract

This study investigates how concrete removal techniques affect substrates of different compositions, and as a result, the bonding with repair mortar. To this end, substrate surfaces of different concrete compositions, micro-concrete (MC), gravel concrete (GC) and crushed stone concrete (CC), were treated by using three commonly used removal techniques; hydrodemolition/water-jetting (WJ), jack-hammering (JH) and grit blasting (GB). Automated laser measurements (ALM) and the volumetric sand patch technique were employed to determine the surface roughness of the substrates. The effect of the substrates parameters such as aggregate size and uniformity on the bonding and failure modes was investigated. Uniformity of the substrates was evaluated by porosity measurements. According to the results, bond strength, surface tensile strength, failure modes and surface roughness were dependent on the aggregate size, aggregate shape and uniformity of mixture. The largest aggregate size and highest porosity along with the highest microcrack density and roughness belonged to CC mixtures. A high correlation was observed between the measured water transport and bond strength of samples. Micro-cracking and a weak interfacial transition zone (ITZ) seem to be the detrimental factors influencing the bond strength of samples treated with JH and WJ, respectively. The influence of WJ on the bond strength was dependent on the mix composition parameters such as aggregate size.