Influence of Surface Roughness on Adhesion Between the Existing and New Plain Concretes

The bonding that exists between the old concrete and the new concrete depends largely on the quality of substrate surface preparation. The accurate representation of substrate surface roughness can help determine very precisely the correct bonding behavior. In this work, the experimental program aimed to investigate the bond strength between two plain concretes, the first one is a concrete substrate as existing concrete, the second one is a new concrete overlay. Four types of original con crete substrate surface preparation were used: as-cast (without surface preparation) as a reference, wire-brushed, grooves and drilled holes. Adhesion strength is quantified at 30 days based on the results of the slant shear test and splitting cylinder tensile test, as well as shrinkage test which was made after 56 days of casting the new overlay concrete. The results generally indicate that the surface roughness of the concrete substrate is very much required to obtain superior mechanical bond of the composites; whereby the concrete with grooves and drilled holes substrate providing the most superior mechanical bond.