Load-deformation behaviour of weft-knitted textile reinforced concrete in uniaxial tension

Weft-knitted textiles offer many advantages over conventional woven fabrics since they allow the fabrication of doubly curved geometries without the need of stitching multiple patches together. This study investigated the use of high-strength continuous fibres as knitted textile reinforcement, focusing on various knitting patterns, fibre materials, coating types and spatial features to enhance the bond conditions between concrete and reinforcement. The bond is of particular interest since the contact surface of knitted textiles is fundamentally different due to their closed surface, compared to commercially available textile reinforcement, which is normally formed as orthogonally woven grids of rovings. An experimental campaign consisting of 28 textile-concrete composites was conducted, where digital image correlation-based measurements were used to assess the load-deformation behaviour and to analyse the crack kinematics. The results showed a beneficial post-cracking behaviour for epoxy coated configurations with straight inlays. The comparison of these configurations with conventional textile reinforcement generally showed a similar behaviour, but with higher utilisation compared to the filament strength. The Tension Chord Model, which assumes a constant bond stress-slip relationship, was adapted for the specific geometry of the knitted reinforcement, and it was used for the estimation of bond stresses and a post-diction of the experimental results, generally showing a good agreement.