Flexural behaviour of hybrid fibre-reinforced recycled aggregate concrete beams with BFRP bars and steel-BFRP composite bars (SBCBs)

Structural application of recycled aggregate concrete (RAC) remains limited due to its reduced strength, durability and ductility compared to natural aggregate concrete (NAC). To overcome these shortcomings, macro-basalt fibres and recycled macro-polypropylene fibres have recently been used to reinforce RAC. In this study, beams made from the developed hybrid fibre-reinforced recycled aggregate concrete (FRRAC) reinforced with basalt fibre-reinforced polymer (BFRP) bars or steel-BFRP composite bars (SBCBs) were fabricated and tested. The flexural performance of 11 beams (including 1 NAC, 5 RAC and 5 FRRAC) with steel, BFRP bars and SBCBs was assessed through a 4-point bending test. The assessed parameters included reinforcement types/ratios and the additional of hybrid fibres. Failure modes, load-deflection response, stress-strain curves, and ductility coefficients of displacement and energy absorption were analysed. BFRP bars and SBCBs significantly increased the beam failure loads by 61 % and 34 %, respectively, compared to steel reinforcement. Hybrid fibres increased the peak loads of BFRP and SBCB-reinforced RAC beams by 33 % and 19 %, respectively, with stiffness improvement by 24 % in BFRP-reinforced beams. Ductility coefficients nearly doubled for SBCB-reinforced beams with hybrid fibres. New empirical formulae were proposed to predict the load-deflection response of RAC and FRRAC beams reinforced with BFRP bars or SBCBs.