Toward green precast concrete production with BFRPmf: latest insights on the effect of fibre dosage on fresh and hardened properties

This paper presents recent insights gained from some activities at QUB within the scope of the "Dispersed Non-Metallic Reinforcement for Energy-Efficient Manufacturing of Precast Concrete" project. These activities focused on developing and optimising fibre-reinforced concrete (FRC) mix designs through variations in basalt fibre-reinforced polymer macro fibre (BFRPmf) dosage. FRC mixes were developed by varying BFRPmf dosages (0.25%, 0.5%, 0.75%, and 1% fibre volume in the mix (Vf)) in a self-compacting concrete (SCC) matrix, and their fresh and hardened properties were measured. Rheological tests including the slump flow test, V-funnel test, and J-ring test were conducted to assess fresh properties. Compressive and tensile strength tests were performed, using the tensile splitting test and direct tensile test (DTT), to evaluate the mechanical properties of hardened concrete. The observations and measurements presented in this paper show that the addition of BFRPmf to the mixes slightly improves the compressive strength of the reinforced concrete in comparison to the reference plain SCC (No Fibre mix). The tensile strength of BFRPmf-reinforced concrete (BmfRC) mixes increases with the increase of macrofibre in the mix. Moreover, a higher fibre dosage improves the post-cracking behaviour and toughness of the BmfRCs, enabling them to carry the load for a longer duration after cracking. The study of rheological and mechanical properties highlights that despite achieving a high tensile strength improvement by adding macrofibre dosages of more than 0.5% Vf to the mixes, the passability and viscosity of fresh mixes are significantly compromised. Therefore, based on this study a fibre dosage of 0.5% Vf is identified as the threshold for optimal mix design.