Assessment of Bond Strength of Underwater Polymer-Modified Concrete

A comprehensive research project was undertaken to evaluate the effect of styrene butadiene rubber (SBR) latex admixture on washout loss and bond strength of underwater concrete (UWC) designated for repair applications. Three UWC series possessing low to high stability levels that incorporate 5 to 15% SBR, by binder mass, were tested. A 1.5 m (4.93 ft) long specially designed channel was developed to enable the UWC to free fall from the outlet of a V-funnel apparatus, flow along an inclined surface submerged in water, then spread onto a horizontal concrete surface. Results show that underwater casting leads to reduced pulloff strengths caused by washout loss and aggregate segregation that weaken in-place properties. The incorporation of SBR was particularly efficient to reduce washout loss and improve adhesion between the repair overlay and substrate. Regression models enabling the prediction of residual bond strengths from the UWC rheological properties, washout loss, and polymer content are established.