An experimental study was performed to evaluate the bond strength between two concrete layers, for different techniques for increasing the roughness of the substrate surface. In a total of 25 slant shear specimens and 25 pull-off specimens the substrate surface was prepared by wire-brushing; sand-blasting; chipping with a light jackhammer; or were left as-cast against steel formwork. Three months later, the new concrete was added. Pull-off tests were performed to evaluate the bond strength in tension. Slant shear tests were conducted to quantify the bond strength in shear. Analysis of results indicated that: the highest value of bond strength was achieved with sand-blasting; pull-off tests are adequate to estimate the bond strength in situ; and pre-wetting the substrate surface does not seem to influence the bond strength.
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