Several systems for suspended precast concrete slabs are designed to receive an in-situ overlay to complete the member and give it its full structural capacity. Guidelines for the surface preparation of hardened concrete members prior to overlay application frequently specify a “saturated surface-dry” condition for optimum bond strength. The laboratory-based research described in this paper identified that a saturated, surface-dry substrate concrete has generally no beneficial influence on overlay bond strength. In many instances, the use of substrate surfaces prepared to what is commonly considered the optimum moisture condition resulted in significantly lower bond strength, compared to non-preconditioned substrates. This phenomenon was ascribed to better mechanical interlock, which exists when the fresh overlay material can flow into the unsaturated cavities and pores of the substrate.
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