Effect of incorporating recycled macro fibres on the properties of ultra-high-performance seawater sea-sand concrete

Ultra-high-performance concrete (UHPC) is an ideal material for constructing marine infrastructures, but faces obstacles such as limited local raw materials (i.e., freshwater and river-sand) and corrosion of steel reinforcement. Non-metallic reinforcement is preferable for reinforcing marine UHPC, especially when seawater and sea-sand are used to develop ultra-high-performance seawater sea-sand concrete (USSC). Recently, the authors' group proposed a cost-efficient UHPC reinforced with discrete macro fibres mechanically processed from waste glass fibre-reinforced polymer (GFRP) composites. This present study aimed to explore the potential application of incorporating macro fibres in USSC. A series of tests were conducted to investigate the fundamental properties of macro fibre reinforced USSC with the examined variables including the content (0 %, 2 %, 4 %, and 6 %) and lengths (30 mm and 60 mm) of macro fibres. Comparisons were made between USSC and UHPC with river-sand and freshwater (UTRC), which were both reinforced with macro fibres. The results revealed that incorporating macro fibres in USSC improved the compressive toughness index (CTI) and flexural toughness by up to 84.00 % and 40.15 times respectively, but decreased the workability and compressive strength by up to 42.22 % and 21.45 % respectively. The effect of incorporating macro fibres on the properties of USSC was more prominent than that of its counterpart of UTRC. A theoretical model was then developed for predicting the flexural toughness of various concrete with macro fibres based on the regression analysis on the available test results. •The effects of incorporating macro fibres on USSC were examined.•The reinforcement effects of macro fibres on USSC and UTRC were compared.•The flexural toughness of beams was predicted using a theoretical model.