Effects of seawater on durability of hybrid C/BFRP-confined seawater–sea sand concrete columns under axial compression

A carbon-fiber-reinforced polymer (CFRP) sheet is wrapped around the basalt-fiber-reinforced polymer (BFRP) to develop a hybrid carbon/basalt-fiber-reinforced polymer (C/BFRP) so as to protect the basalt fibers in touch with chloride ions. Tensile testing is conducted on the BFRP and hybrid C/BFRP sheets. The effect of the durability of the fiber-reinforced polymer sheet on the behavior of the seawater–sea sand concrete (SSC) columns confined by the BFRP and hybrid C/BFRP sheets is examined using axial compression testing. The tensile strength retention and elongation at break retention of the hybrid C/BFRP sheet improve by 41% and 24% higher than those of the BFRP sheet after 12 months in seawater. The ultimate strength of the BFRP-confined SSC column decline by 40% more than those of the hybrid C/BFRP-confined SSC column respectively, after 12 months of seawater immersion, resulting from the reduction of lateral pressure provided by the BFRP and hybrid C/BFRP sheets in seawater. A formula for calculating the long-term ultimate strength and ultimate strain of the FRP-confined SSC column is proposed, and its predictions agree well with the test results. The hybrid C/BFRP sheet proves more efficient than the BFRP sheet in confining the seawater–sea sand concrete columns.