Rate-dependence of the tensile behaviour of fibre reinforced concrete in the quasi-static regime

The effect of crack rate on the tensile stress-crack width relation of fibre reinforced concrete is studied experimentally, using the three-point bending test, where the post-peak flexural response of the material is determined over a range of loading rates covering 5 orders of magnitude. The tetralinear stress-crack opening (sigma-omega) relations are subsequently obtained from inverse analyses. Concretes with hooked-ended steel fibres at different dosages and with polypropylene fibres have been studied. The results show that the tensile strength is reduced and the initial drop in cohesive stresses is less steep at slower loading rates, with the changes being more significant in concretes with lower toughness. Numerical analysis shows that the fracture process zone at crack initiation extends further as the loading becomes slower. The variation in the sigma-omega relation with crack rate has been modelled empirically based on the rate-dependence of the concrete matrix and the tensile strength of the FRC. The general variation of flexural toughness with the loading rate has also been identified, reflecting the moderating influence due to steel fibres, especially at higher dosages.