Experimental and Theoretical Research on Low-Strength Concrete Beams Reinforced with Basalt Fibre-Reinforced Plastic Sheets in a Freeze–Thaw Environment

Basalt fibre-reinforced plastic sheet (BFRP) enhancement is one of the strengthening methods suitable for concrete structures due to the low price and high tensile strength of BFRPs. It is of great importance to study the mechanical performance of BFRP-reinforced low-strength concrete structures in freeze–thaw environments. Therefore, 15 concrete beam specimens were designed, and a fast freeze–thaw experiment was conducted in this research to consider different parameters, such as the number of freeze–thaw cycles, sequence of freezing–thawing and BFRP pasting and other factors. The mechanical performance of low-strength concrete beams reinforced with BFRPs under freeze–thaw cycles was investigated. The failure mode and load–deflection curves of specimens were also analysed. The test results revealed that the ultimate strength of concrete beams reinforced with BFRPs was greatly improved, with a maximum increase of 32.7%. With increasing number of freeze–thaw cycles, the ultimate strength of beams gradually decreased over the bearing capacity of non-frozen-thawed concrete beams reinforced with BFRPs (F0b), and the bearing capacity of low-strength concrete beams reinforced with BFRPs decreased 17.1% after 50 continuous freeze–thaw cycles, while the beam failure mode changed from bending failure to shear failure accompanied by de-bonding failure. A mechanical model of BFRP-reinforced low-strength concrete beams was constructed under the de-bonding failure mode, and a calculation equation to determine the magnitude of de-bonding failure was proposed. Finally, finite element analysis of specimens was performed with cohesive elements to simulate the nonlinear softening mechanical behaviour of the BFRP–concrete interface.