Experimental investigation of the bond strength between new to old concrete using different adhesive layers

This work was designed to evaluate the performance of adhesive layers between substrate concrete and freshly overlaid concrete, under the action of tensile and shear stresses. Four types of adhesive layers that are frequently used in real applications (i.e., cement paste, epoxy bonding agent, styrene butadiene rubber (SBR)-latex and carbon fiber reinforced polymer (CFRP)) were selected. Composite specimens were tested to evaluate their performance under tension, shear and tension-shear stress by split, bi-surface and slant shear strength tests. SBR-latex showed a promising result for repaired systems under the combined action of tensile and shear stresses due to its superior adhesive property via the formation of a polymer film. As expected, CFRP showed the highest strength when such composite systems were under the action of tensile or shear stresses and had a strong potential for use for jointing precast members. Cement paste, which is a widely used adhesive repair material, showed poor resistance in the tension test due to its brittle nature. In addition, the roughness of the fractured surfaces was quantified and the failure modes were explained at the meso-level. The outcomes of this work may guide designers in the selection of appropriate types of adhesive layers for a composite structure that may be under tensile, shear or tensile-shear stress.