Effect of surface preparation techniques on the cohesion of superficial concrete: comparison between jack-hammering and water-jetting

The aim of concrete surface preparation is to obtain a surface with properties similar to those of the bulk concrete. Superficial concrete must be sound, dry, cohesive and contaminant-free. Particularly, the preparation must be performed in such a way that sound and homogeneous concrete is reached. The most widespread surface preparation techniques are sandblasting, jack-hammering, milling and other water hydro-jetting. Evaluation of the effect of surface preparation is often based upon surface roughness or specific sur-face. It is necessary however to investigate further within the first few centimetres from the surface to verify the concrete homogeneity and soundness. Pull-off test is a destructive method that can be useful for such evaluation, but it only gives an indication; the observation of the failure mode is more instructive. This paper summarizes the results of a microscopy investigation performed to quantify the number and length of cracks. The analysis leads to the comparison of jack-hammering and water-jetting techniques in terms of their poten-tial effect on superficial cohesion of concrete.