Study On Bond Performance Between Corroded Steel Bar And Basalt Fiber Reinforced Concrete After Elevated Temperatures

The marine atmosphere is a salt spray environment with high chloride ion content.Long-term service of reinforced concrete structures in this environment will lead to the invasion of chloride ions,resulting in the internal corrosion of steel bars.If such structures(such as tunnel structures)suffer from fire damage during their service life,it becomes a complex engineering problem characterized by the coupling of corrosion damage and high-temperature effects of fire,which will seriously deteriorate the bond performance between steel bar and concrete,and threaten the integrity and safety of the structure.Basalt fiber reinforced concrete(BFRC)is a new type of concrete material.Research on the bond performance of steel bars and BFRC under coupled conditions will not only improve the fiber theory system and promote its application,but also provide a more comprehensive reference for the safety assessment of structures that require a high level of durability under fire conditions,such as sub-sea tunnels.This thesis investigates the effects of elevated temperatures and corrosion on the bond performance between steel bars and BFRC.The main research contents and findings are as follows:The pull-out test of steel bar and BFRC after elevated temperatures and the test of mechanical properties of BFRC after elevated temperatures were carried out to analyze the effects of different temperatures and volume fractions of basalt fibers on the bond performance of the test specimens and mechanical properties of the concrete.The results show that while the temperature above 500°C leads to severe deterioration of bond performance of the test specimens and the mechanical properties of concrete.With the increase of temperature,the bond strength of the test specimens and the splitting tensile strength of concrete show similar degradation patterns.At room temperature,basalt fiber has no significant effect on the bond performance of the test specimens,but it can inhibit the deterioration of the bond performance of test specimens after experiencing elevated temperature damage.The test specimens with 0.15% fiber volume fraction show the most excellent bond performance.The pull-out test of corroded steel bars and BFRC after elevated temperatures was conducted to analyze the impact of the coupled effect of elevated temperature and corrosion on the bond performance between steel bars and concrete.The results show that at 20℃ to 300℃,the bond strength of the test specimens first increases and then decreases with the increase of corrosion rate of steel bar;When the temperature is higher than 500℃,the bond strength of the test specimens continuously decreases as the corrosion rate increase,and the improvement effect of mild corrosion on the bond performance disappears.In addition,the severe coupled damage makes the improvement effect of basalt fibers on bonding performance no longer significant.A three-stage constitutive model of bond-slip between corroded steel bar and BFRC after the elevated temperatures was established,and the performance parameters such as bond strength and peak slip of the test specimens under different working conditions were fitted according to the least squares method,and the three-stage benchmark model was modified by introducing the dual influence coefficients of elevated temperature and corrosion rate of steel bar.The model curve was verified to be in good agreement with the experimental curve.Through ABAQUS numerical simulation software,the structural model of reinforced concrete beams under different temperatures and corrosion conditions was established,the effects of different contact modes between steel bar and concrete,i.e.,the built-in reinforcement and the consideration of bond-slip on the mechanical response of the beams were simulated and analyzed,and the applicability of the bondslip constitutive model was verified.