Deterioration of basalt/carbon-based hybrid-FRP bars in a simulated pore solution of seawater sea-sand concrete

Hybrid-fibre-reinforced polymer (HFRP) bars comprising basalt and carbon fibres are expected to be more durable than BFRP bars in seawater sea-sand concrete (SWSC) environments. This study was aimed at investigating the effects of carbon-fibre content on the durability of newly developed HFRP bars conditioned in a simulated SWSC pore solution. Tensile strength was adopted as a measure of the degree of deterioration and correlated with water uptake. The deterioration mechanism was analysed by digital microscopy (DM), Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, matrix digestion analysis, and inductively coupled plasma mass spectrometry (ICP-MS). The results indicated that increasing the carbon-fibre content clearly reduced the water uptake and tensile strength attenuation rate of the HFRP bars. An unambiguous correlation was established between tensile strength and water uptake. The resin swelled, hydrolysed, and plasticised after absorbing water, which initiated the deterioration of the HFRP bars. The annular basalt–carbon-fibre interfacial areas in the HFRP bars alleviated their overall deterioration but induced local degradation. The findings of this study provide insight into the development of FRP materials with improved durability.