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The bond strength of concrete-to-concrete interfaces, of reinforced concrete (RC) members with parts cast at different ages, is highly influenced by the curing conditions. Therefore, the monolithic behavior is dependent on these conditions. Current design codes only consider: a) the concrete compressive strength; b) the normal stress at the interface; c) the amount of reinforcement crossing the interface; and d) the roughness of the substrate surface. Because the curing conditions of both substrate and added concrete are ignored, the influence of the differential shrinkage is neglected. The influence of the differential stiffness due to the mismatch between the Young’s modulus of both materials is not considered either. This paper presents an experimental study conducted to assess the influence of differential shrinkage and stiffness on the bond strength of new-to-old concrete interfaces. Both parameters were shown to have a significant influence on the bond strength and failure mode of concrete-to-concrete interfaces.
Santos et al. (Sat,) studied this question.