Mechanical properties of fibre reinforced seawater sea-sand recycled aggregate concrete under axial compression

This study investigates the mechanical properties of fibre reinforced seawater sea-sand recycled aggregate concrete (SSRAC). A total of 360 concrete specimens, considering four different variables-the type of concrete (SSRAC, recycled aggregate concrete and ordinary concrete), age (day 7, 14 and 28), fibre type (polypropylene and stainless steel fibres) and content-were fabricated. The macro properties and mechanical mechanism of discrete fibre reinforced SSRAC were systematically studied through a novel experimental system involving axial compression test and digital speckle correlation method (DSCM). The failure pattern, strength, ductility, stress-strain curve, deformation filed, crack initiation and propagation of fibre reinforced SSRAC were analysed. The major research findings indicate that the stainless steel fibres (SSF) could effectively offset the effects of seawater, sea-sand and recycled aggregates on the mechanical properties of concrete compared to polypropylene fibres (PF). The failure pattern of specimen slightly changed with the fibre type used. The compressive and splitting tensile strengths of SSRAC increased with an increase in PF content, while the optimal SSF content for SSRAC was 1.0% by volume content of concrete. Moreover, the typical influence of PF on the elastic modulus of SSRAC was negative but SSF could greatly improve that of specimen. The axial stress-strain curve of fibre reinforced SSRAC consisted of elastic, elastic-plastic ascending and declining stages. Increasing SSF and PF contents decreased the curve curvature while increased the ductility and peak strain, and the descending branch of curve tended to be smooth. Generally, the effects of fibres on the crack initiation of SSRAC and the distributions of deformation field and cracks were negligible compared to coarse aggregates, while the crack propagation of SSRAC significantly changed with the variations in fibre type and content. The cracks and high-value strain of SSF reinforced SSRAC developed slowly compared to plain SSRAC and PF reinforced SSRAC. Finally, an analytical stress-strain model of fibre reinforced SSRAC considering the coupled effects of various variables were proposed, which can be used to conduct a theoretical evaluation and design of the marine structures.

Automated summary

This study systematically investigates the mechanical properties of fibre reinforced seawater sea-sand recycled aggregate concrete. The research findings indicate that stainless steel fibres can effectively offset the effects of seawater, sea-sand, and recycled aggregates on the concrete's mechanical properties. The fibre content affects the strength and ductility of the concrete, while the fibre type changes the failure pattern and crack propagation speed.