Bond and tensile properties of flax textile reinforced recycled aggregate concrete: Strategies for interfacial enhancement and corresponding mechanisms

This study investigated the bond properties between flax fibre reinforced polymer (FFRP) mesh and various cementitious matrices, examining the impact of incorporating medium-sized recycled aggregates (2 - 8 mm). Enhancement strategies included modifying the FFRP surface with rice husk ash (RHA) and incorporating RHA into the cementitious matrix. Pull-out and uniaxial tensile tests were performed on FFRP reinforced mortar, FFRP reinforced recycled aggregate concrete (RAC), RAC reinforced with RHA-modified FFRP and RAC (containing RHA) reinforced with RHA-modified FFRP. The results showed that FFRP surface modification with RHA significantly improved bond strength, by 32 % compared to pulling normal FFRP from RAC. This was attributed to increased surface roughness of FFRP, enhanced chemical bonding due to pozzolanic reaction of RHA, and improved interfacial transition zone resulting from increased wettability and decreased water absorption ratio of the treated FFRP. Additionally, the inclusion of medium-sized recycled aggregates mitigated debonding by enhancing mechanical interlocking with the FFRP mesh. Compared to FFRP reinforced mortar, FFRP reinforced RAC and RHA-modified FFRP reinforced RAC exhibited increased strain capacity and refined crack propagation, indicating improved stress distribution. However, the enhanced anchoring reduced tensile strength by restricting the full utilisation of strain capacity in the post-cracking phase. These findings highlight the potential of surface modification of reinforcement with supplementary cementitious materials and the incorporation of medium recycled aggregates in the matrix to enhance bond performance and optimise the mechanical behaviour of cementitious composites.