Degradation of the axial compressive performance of BFRP bars-reinforced concrete columns after freeze-thaw cycling

This work investigated the effects of freeze-thaw (F-T) cycling numbers, reinforcement ratio of BFRP bars, and the strength of concrete matrix on the mechanical performance of columns under axial compression. Herein 12 columns were designed and tested after they served 0, 100, 200, and 300 times of F-T cycling. Experimental results included the stiffness, load-bearing capacity, ductility and load-displacement curves, which revealed an obvious degradation of columns' axial compressive performance under F-T cycling. This degradation was considered in the structural design of the columns, and an in-depth study provided a numerical model of the tested specimen developed using the finite element method validated by test results. Both of the tests and numerical results revealed that the degradation of the columns' performance, including the initial stiffness, the load-bearing capacity, and the ductility, became more significant when the F-T cycling increased. Deterioration of the concrete and its bonding with basalt fiber reinforced polymer (BFRP) rebar were considered as the crucial factors responsible for the failure of columns after F-T cycling. After being subjected to F-T cycles, the initial stiffness and the load-bearing capacity of BFRP bar-reinforced short columns can be improved by higher strength of concrete and larger diameter of BFRP bars to some extent. Finally, an analytical calculation method was introduced for estimating the axial compressive capacity of BFRP bars-reinforced concrete columns after F-T cycling, which can supply a theoretical foundation for the design and application of BFRP bars in concrete structures.