Complex salt frost resistance of pre-damaged reinforced HPC columns wrapped with BFRP sheets

Fibre-reinforced polymer (FRP) sheets have been extensively used to strengthen existing structures in harsh environments (e.g., freeze–thaw and chemical attacks) due to their excellent mechanical properties and durability. However, the effects of FRP sheets on strengthening reinforced concrete columns eroded by chloride and sulphate ions in freeze–thaw environments remain ambiguous. Therefore, this paper investigates the salt frost resistance of basalt fibre-reinforced polymer (BFRP)-reinforced columns subjected to complex salt-frozen environment. The effects of the freeze–thaw medium, reinforcement method, and pre-damage degree on the salt frost resistance of the columns were evaluated, followed by revealing the freeze–thaw damage mechanism of the columns eroded by sulphate and chloride. Moreover, the correlation between the durability and the mechanical properties of the columns wrapped with BFRP sheets was analysed. Results indicate higher concentrations of sodium chloride and sodium sulphate solutions decelerate the deterioration of high-performance concrete (HPC). The double-layer BFRP sheet wrapping method increases the ultimate load of the columns by 84.8%. The partially damaged epoxy resin coatings can serve as a protective layer for the concrete. The ultimate-transition stress ratio of columns wrapped with double-layer BFRP sheets can be used as an index to evaluate the durability. The proposed BFRP retrofit method demonstrates significant potential for enhancing the durability of HPC in salt frost regions. This method provides a theoretical basis for the durability design of reinforced HPC columns wrapped with BFRP sheets in salt frost regions.