Mechanical properties and flexural toughness evaluation method of mono/ hybrid fiber-reinforced ultra-high performance seawater sea sand concrete

Ultra-high performance seawater sea sand concrete (UHPSSC) is an advanced cementitious composite material exhibiting superior mechanical and durability properties, particularly suited for marine constructions challenged by the scarcity of freshwater and river sand. This study aims to examine the impact of fiber reinforcement on the mechanical properties of UHPSSC and to evaluate the method of assessing flexural toughness. In this paper, the effects of end-hooked steel fiber (HF), corrugated steel fiber (CF), straight steel fiber (SF), and PVA fiber (PVAF) as mono/hybrid reinforcements on the mechanical properties of UHPSSC were investigated. The microstructures of fiber-reinforced UHPSSC are characterized by scanning electron microscopy. A two-stage energy ratio (TER) flexural toughness assessment method is proposed based on the energy ratio method. The results indicate that mono/hybrid fibers significantly influence the mechanical properties of UHPSSC. SF and HF effectively enhance the compressive and flexural strengths. Microstructural observations confirm the bridging effect and pullout behavior of the fibers within the matrix. In hybrid fiber systems, strength and flexural toughness increase with higher SF doping levels. The maximum synergistic effect is observed at an SF doping level of 1.5 vol%. The TER method, characterized by clear physical meaning and strong applicability, enables the evaluation of the toughening effect of fibers on UHPSSC at various deflections, thereby facilitating the design of UHPSSC for marine and coastal structures.