An experimental study on interfacial bond strength between hybrid engineered cementitious composite and concrete

•Bond behaviours of PVA-ECC and SPH-ECC with concrete studied experimentally.•Qualitative and quantitative surface roughness measurements of concrete discussed.•Effects of ECC types and sandblasting on bond strength with concrete studied.•Empirical equations predicting bond strength between ECCs and concrete proposed. In this research, an experimental study was conducted to investigate the interfacial bond strength of polyvinyl-alcohol fibre reinforced engineered cementitious composite (PVA-ECC) and steel-polyvinyl alcohol hybrid fibre reinforced engineered cementitious composite (SPH-ECC) to compare the effects of using hybrid fibre ECC against mono-fibre ECC and aiming to promising and effective retrofitting material for reinforced concrete structures. Slant shear tests and splitting tensile tests were performed to study the shear bonding and splitting tensile bonding behaviours, respectively. The effect of surface roughness of the concrete surface on bond strength was also studied by measuring the bond strength of surfaces with different roughness under the As-Cast (AC) and Sandblasted (SB) surface treatment conditions. Interfacial surface roughness was measured using both quantitative and qualitative assessment methods. Experimental results obtained shown that sandblasting could greatly increase the roughness of concrete surfaces and lead to bond strength enhancement for both types of ECC-concrete interfaces. In addition, it was also found that for sandblasted surface, more significant increase was observed for the SPH-ECC interface due to dowel actions of the steel fibre. This indicated that SPH-ECC is a more suitable repairing/retrofitting material than PVA-ECC when sandblasting is applied. Finally, by using logarithmic regression, empirical relationships were proposed to predict the relationships of interfacial shear bond strength with the surface roughness of concrete.