Impacts of interfacial bonding between concrete substrate and cast/sprayable HPFRCC on flexural behaviour

The performance of repair materials is greatly enhanced by the integrity of the rehabilitation system, which depends on the behaviour of the boundary or interface bond between the repair material and the concrete substrate. The current study investigated the effect of implementation method of repair materials (cast or spray method), spraying direction, and concrete substrate roughness on the interfacial bond behaviour experimentally by using the four-point bending test on prism samples with dimensions of 300×76.2×40 mm. At first, the concrete substrate was made with a thickness of 2 cm, and its surface was considered proportional to the five surfaces. After 28 days curing, the repair material was poured into specific molds and sprayed. The repair material used herein was a high-performance (high ductility) fibre-reinforced cementitious composite (HPFRCC) developed with local materials and a tensile strain capacity of 3.7%. The results demonstrated that spraying direction and surface roughness of the concrete substrate significantly impact the ultimate deflection rate; upward spraying had the lowest and downward spraying the highest deflection rate. Furthermore, because beams are often repaired from the lower part, and the spraying is upward, the cast method must be used because of the negative effect of gravity on the interfacial bonding between the concrete substrate and the repair material.