Steel corrosion could not only result in severe structural damage and huge economic loss but also threaten the safety of structures over their lifetimes. In contrast, glass fiber reinforced polymer (GFRP) presents advantages in high strength-to-weight ratio and good chemical resistance. With these merits, GFRP rebar is considered a substitute for steel reinforcement in concrete structures to address the steel corrosion issue. Particularly, Recently, GFRP rebars have been considered for the construction of major reinforced concrete structures. However, many researchers found that the tensile strength of GFRP rebars inside concrete might gradually decrease with time, i.e., the durability of GFRP rebars is still under the threat of aggressive environmental conditions.



Seawater sea-sand concrete (SWSSC) has also attracted the attention of worldwide researchers because it can make use of seawater and sea sand which are enormously reserved in nature. GFRP-SWSSC structure is believed to be highly promising since salt-induced steel corrosion can be effectively avoided. However, as there are a lot of cations (e.g., Na⁺, K⁺ and Ca²⁺) and anions (e.g., Cl^- and SO₄^2-) in seawater and sea sand, research on the durability of GFRP rebars in SWSSC is complex and challenging.



The purpose of this paper is to investigate the effects of SSC on the durability of GFRP rebars and reveal the potential degradation mechanisms. Firstly, the GFRP rebars are immersed in the simulated pore solution (pH = 13.6) of normal concrete (NC) and SWSSC at 23, 40 and 60 ℃ for up to 12 months. The tensile strength reduction is found to be similar for GFRP rebars exposed to NC and SWSSC solutions (Fig. 1), indicating that the salt content in SWSSC has no significant effect on the tensile performance of GFRP rebars. To confirm this finding, the microstructure morphology and chemical compositions of SWSSC-GFRP samples are observed by conducting scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) tests, respectively. As a result, strong chemical reactions between ions and the glass fibers and matrix mostly occur on the rebar’s exterior, while the rebar’s core basically remains unchanged (Fig. 2). Further, the compared GFRP rebars are immersed in distilled water (pH = 7) and sodium hydroxide solutions (pH = 11, 12 and 13) at 23, 40 and 60 ℃ for up to 12 months, which is conducted to illustrate the effect of exposure pH level on GFRP’s degradation. Experimental results show smaller tensile strength retention in a high-pH exposure (Fig. 3), implying that a higher pH level could result in more severe corrosion. In addition, the residual tensile strength retention of GFRP rebars is found to follow an exponential function with the ambient pH level (Fig. 4). Lastly, the activation energy (E_a) corresponding to the GFRP corrosion at different pH levels is obtained based on Arrhenius equation, and the relationship between E_a and pH level is found to reveal the degradation mechanism behind the GFRP corrosion. As E_a linearly decreases with increasing pH level and both NC- and SWSSC- GFRP samples obey the same function (Fig. 4), the GFRP corrosion of rebars in NC and SWSSC is believed to be attributed to the cementitious alkalinity.



Based on the bench-scaled investigation, this study reveals that GFRP corrosion is mainly attributed to the exposure pH level, but the seawater sea-sand slightly affects the durability of GFRP. This study yields useful information to engineers regarding the degradation mechanism of GFRP corrosion. The measurement of ambient pH is believed to be an effective method to rapidly estimate the potential GFRP corrosion.