Factors affecting the fresh-to-hardened concrete repair system

This paper reviews the bonding performance inside the layered concrete elements where the bonding agents, substrate moisture condition, overlay time (contact time) and the other influencing factors, are discussed. Higher aggressive treatments need to be avoided in the lower classes of concrete substrates. The surface tensile strength of the substrate should be recorded before placing a new concrete, to describe its quality and validity for strengthening, rather than measuring the density of microcracks. Higher gap of compressive strength between overlay and substrate was found increasing the bond strength and the cohesive failure tendency. Overlays with lower w/c ratio developed higher compressive strength, but lower bond strength was found. The review study concluded adding silica fume, or latex to the overlay was found increasing the bond strength. Overlays containing fibers can produce higher bond strength results due the drying shrinkages' reduction by fibers. A conflict of results was concluded regarding the effect of the moisture condition, surface roughness and adhesives on the bond strength. Flexible adhesives are more recommended than rigid ones, despite the relatively lower developed bond strength.

Automated summary

This paper reviews the factors influencing bonding performance inside layered concrete elements, suggesting avoiding overly aggressive treatments for lower class concrete substrates and emphasizing the importance of measuring the substrate surface tensile strength. It also highlights the impact of the compressive strength gap between overlay and substrate on bonding strength.