Mitigating the deterioration of BFRP bars in seawater sea sand mortar by reducing alkalinity

Abstract

The susceptibility of BFRP bars in alkaline cementitious environment restricts their application as reinforcing materials in marine construction. To address this problem, the internal alkalinity of seawater sea sand mortars (SWSSM) is controlled in this study through optimization of cementitious materials for the durability enhancement of BFRP bars Accelerated aging tests were conducted to evaluate the durability of BFRP bars embedded in normal and low-alkalinity SWSSM. The mechanical and physiochemical deterioration of the embedded BFRP bars under various exposure periods (3, 6, and 8 months) and temperatures (25, 40, and 55 °C) were studied through interlaminar shear strength test, Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. At 25 °C, the interlaminar shear strength retentions after 240-day exposure for BFRP bars embedded in low-alkalinity SWSSMs with pHs of 11.6 and 11.1 are 4.76 % and 7.20% greater than those of in normal SWSSM (pH of 12.5), respectively. The interlaminar shear strength retentions of BFRP samples in the low-alkalinity groups are 24.71% and 24.54% more than those in the high-alkalinity group at 40 °C, and 45.64% and 41.98% more at 55 °C, respectively. The enhancing effect can be more significant under higher exposure temperature for normal SWSSM, but not for the low-alkalinity SWSSMs. The low-alkalinity SWSSMs help to minimize the degradation of embedded BFRP bars by reducing resin hydrolysis and fiber-resin interface debonding. Moreover, the model of Arrhenius theory predicts that the interlaminar shear strength retention of BFRP bars embedded in the normal SWSSM will decrease to 70% less than 2 years, while that of those embedded in low-alkalinity SWSSMs will maintain more than 80%. This study provides insights into using low-alkalinity cementitious materials to mitigate the deterioration of embedded BFRP bars and to extend their service life in marine concrete structures.