Title:
Alkalinity Dependence Analysis of Degradation of Glass Fiber-Reinforced Polymer Bars (Prepublished)
Author(s):
Yong Yi, Sheng Li, Xinxin Zhan, Xing Chen, Deju Zhu
Publication:
Materials Journal
Volume:
Issue:
Appears on pages(s):
Keywords:
alkalinity; degradation; GFRP bar; marine; predictive model
DOI:
10.14359/51750706
Date:
4/30/2026
Abstract:
The alkali resistance of glass fiber-reinforced polymer (GFRP) bars is a key property that must be evaluated before they can be used as an alternative to steel reinforcement in marine concrete structures. To clarify the effect of alkalinity on GFRP bars, their durability was investigated via accelerated aging in simulated seawater sea-sand concrete environments with different alkalinity levels. The physical and mechanical properties, including moisture uptake, interlaminar shear strength, transverse shear strength, and tensile strength of GFRP bars, were measured after exposure to solutions with pH values of 10.1, 12.3, and 13.2. Furthermore, microstructural deterioration was analyzed using Fourier transform infrared spectroscopy and scanning electron microscopy. A refined predictive model based on reaction kinetics and Arrhenius theory was proposed to quantify the role of alkalinity. The results indicated that the degradation of GFRP bars is highly sensitive to alkalinity. When the pH decreased from 13.2 to 12.3, the deterioration in mechanical strength was reduced by more than 60%, accompanied by significantly mitigated glass fiber etching. Below a threshold between high and moderate alkalinity, this sensitivity diminished as alkalinity decreased. The loss of mechanical properties was reduced by only about 10% when the solution pH dropped from 12.3 to 10.1, with clear alleviation of resin disintegration and fiber surface corrosion. Within the typical alkalinity range of ordinary concrete, the degradation rate follows a power function of the hydroxyl ion concentration. The effect on the degradation rate is much greater within the concentration range of 0.1 mol/L to 0.01 mol/L (pH ≈ 13.0-pH ≈ 12.0) than below 0.01 mol/L (pH ≤ 12.0). It is therefore recommended to keep the hydroxyl ion concentration in concrete pore solution below 0.01 mol/L (pH ≈ 12.0) to minimize alkaline attack on embedded GFRP bars.