Inverse analysis-based model for the tensile behaviour of fibre-reinforced concrete with manufactured and waste tyres recovered fibres

The urgency of finding green solutions within the construction industry encouraged, in latest years, the adoption of sustainable materials for structural concrete. One of the most up-and-coming proposal is the use of recycled steel fibres, to complement or possibly replace tradi-tional steel reinforcement. Nevertheless, the contribution of the fibres on the mechanical per-formance of concrete is still uncertain and requires further investigation. This study is aimed at providing an analytical model for the tensile response of concrete reinforced with manufactured steel fibres and recycled steel fibres recovered from waste tyres. The proposed model features several parameters ruling the cracking strength, the post cracking behaviour and the residual tensile strength of fibre-reinforced concrete. The parameters in the analytical model were cali-brated by numerical simulation of toughness tests on specimens with different types and contents of fibres in the mixture. A satisfactory simulation of experimental load-crack tip opening displacement curves was obtained, with numerical-vs-experimental curve scatter lower than 10%. However, the variability of experimental results hindered obtaining an accurate blind simulation of additional tests selected from the literature. On the other hand, a clear correlation between the parameters ruling the cracking strength-to-residual strength ratio and fibres amount was identi-fied for both recycled and manufactured fibres. The outcome of this study showed that the pro-posed model can be used in simplified design approaches, to account for the fibres' type and content in the evaluation of tensile response of fibre reinforced concrete.