Existing concrete textures: their effect on adhesion with fibre concrete overlay

This paper quantifies the roughness parameters of existing normal concrete substrate surfaces and evaluates their effect on adhesion strength with ultra-high-performance fibre concrete overlay. Three types of substrate surface textures are adopted: as-cast texture as control, wire-brushed texture and sand-blasted texture. The roughness profile of these substrate surfaces is assessed using an Alicona Infinite Focus device. Adhesion strength is quantified at 3, 7, 28 and 180 days based on the results of the pull-off test, splitting cylinder tensile test and slant shear test. The short- and long-term results of the splitting cylinder tensile and slant shear tests demonstrate that the surface texture profiles of the existing concrete substrate have an important effect on the adhesion strength between existing concrete and ultra-high-performance fibre concrete overlay. The behaviour of bonded ultra-high-performance fibre concrete/existing concrete with sand-blasted texture closely resembles that of monolithic normal samples under splitting cylinder and slant shear tests. The short- and long-term results of the pull-off test prove that failure occurs in the existing concrete, regardless of the type of existing concrete surface texture. A very good polynomial correlation (R² > 80%) is observed between the average roughness parameter (R_a) of existing concrete textures and results of the splitting cylinder tensile and slant shear tests.