Effect of alkalinity on the shear performance degradation of basalt fiber-reinforced polymer bars in simulated seawater sea sand concrete environment

Abstract

The durability of the basalt fiber-reinforced polymer (BFRP) bar in an alkaline environment is a major problem that prohibits its use as reinforcement in a marine concrete structure. One potential remedy is to reduce the alkalinity of the concrete. For evaluating the feasibility of this technique, the mechanical durability of BFRP bars was investigated in a simulated seawater sea sand concrete environment using accelerated degradation tests. The interlaminar and transverse shear strengths after various exposure times were measured to determine the degree of degradation. The moisture uptake test was also conducted to show the moisture content of the conditioned BFRP bar. Furthermore, the deterioration of matrix and basalt fiber was analyzed by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and inductively-coupled plasma mass spectrometry. The findings showed that reducing alkalinity effectively mitigates moisture uptake, the loss in interlaminar shear strength, and transverse shear strength of BFRP bars. The moisture absorption of BFRP bars is reduced from 5.47% to 0.14% by lowering the pH from 13.2 to 10.1. BFRP bars exposed to the solution with a pH of 13.2 lose the maximum interlaminar and transverse shear strengths, which are 47.08% and 6.17% greater than those with the pH of 10.1. The intensity of alkaline disintegration reactions is considerably declined at the pH of 12.3, whereas the alkalinity-related degradation is marginal at the pH of 10.1. The outcomes of this study indicate that applying this approach can lower epoxy resin degradation while also mitigating basalt fiber etching. This study can also provide insight into the use of low-alkalinity concrete to enhance the long-term performance of FRP bars in concrete structures.