Flexural behaviour of concrete beams repaired by hybrid fibre reinforced cementitious composites (HFRCCs) and subjected to simulated seawater dry-wet cycles

To develop innovative strategies for enhancing the durability of marine concrete structures, hybrid fibre-reinforced cement-based composites (HFRCCs) were used to repair small concrete beams. This study investigated the effects of steel fibre content (0 % to 0.5 % by volume) combined with 1.5vt% polyvinyl alcohol (PVA) fibres, HFRCC layer depth (0–50 mm) and simulated seawater dry-wet cycles (0−40) on the flexural behaviour of repaired beams, with three specimens per series). Results indicated that increasing steel fibre content from 0 % to 0.5 % by volume improved both flexural strength and deflection-hardening behaviour. The optimal composition - 0.15 % steel fibres and 1.5 % PVA fibres, both by volumes - enhanced flexural strength by up to 20 %. A 52 % increase in flexural strength was achieved by increasing the HFRCC layer depth to 30 mm in beams with 0.25 % steel fibres and 1.5 % PVA fibres. Beams with 0.15 % steel fibres and 1.5 % PVA fibres exhibited superior deflection-hardening behaviour, characterised by significant strength gains and enhanced post-cracking toughness. Seawater exposure up to 20 cycles initially increased flexural strength due to continued hydration, while prolonged exposure to 40 cycles reduced flexural strength by 24 %, likely due to chloride accumulation in matrix pores. Based on these parameters, a new equation for predicting the flexural strengths of repaired beams was proposed. Finally, strain analysis confirmed strong compatibility between the HFRCC layer and concrete, improving durability and load-bearing capacity of repaired beams in marine environments. These findings contribute to optimised repair strategies for marine concrete structures, enhancing resilience and structural integrity in harsh environments.