Bond behavior between basalt fiber-reinforced polymer rebars and coral-reef-sand concrete conditioned in saline solution

This paper studies the bond behavior between basalt fiber-reinforced polymer (BFRP) rebars and coral-reef-sand (CRS) concrete exposed to a saline environment. The gradation and mix proportion of CRS concrete was firstly selected, through compressive tests on CRS concrete cubes. A series of pullout tests were conducted on a total of 84 pullout specimens after conditioning in a saline solution. The experimental variables included type of rebar (steel and BFRP), diameter of BFRP rebar, conditioning duration and temperature, and type of conditioning (continuous immersion and wet-dry cycle). The stress-slip curves and bond strength of the pullout specimens were analyzed and discussed. The results show that 0.54 is selected as the water/cement ratio for CRS concrete, among the range of analyzed concrete mixes. The bond behaviors of BFRP rebars depend on their diameter. BFRP rebars with 12-mm-diameter have the best bond durability after conditioning in a saline solution, when compared with their counterparts with 8- and 16-mm-diameters. The effects of conditioning temperature and type of conditioning on the bond behavior of 12-mm-diameter BFRP rebar are negligible. A design-oriented formula was proposed for the prediction of the development length of a BFRP rebar in CRS concrete based on the experimental data. Furthermore, modified BPE models were calibrated to describe the bond-slip relationship of BFRP rebars in CRS concrete in a saline environment.