The use of Glass Fiber Reinforced Plastics (GFRP) bars in coastal concrete structures can effectively prevent steel reinforcement corrosion, but research on the evolution of their performance in seawater and alkaline concrete environments is lacking. The analysis of the degradation process and mechanism of GFRP is thoroughly conducted in this paper through various characterization methods of morphology, mechanics, and material tests. Furthermore, the degradation law of GFRP in various erosion environments is assessed via multi-dimensional indexes. The findings indicate that the erosion of GFRP in an alkaline environment result in the debonding of resin and fiber, thereby causing the formation of cracks. As the erosion age and OH- concentration increase, the size of the cracks expands. Since the dissolution rate of the resin composed as part of GFRP is very low, the salt in seawater has minimal impact on the degradation of GFRP. Vickers hardness of the fiber with age decreased linearly and remained unchanged. Meanwhile, Vickers hardness of the resin with age can be divided into three stages: linear decline stage, linear rise stage, and stabilization stage. Under the erosive conditions, a hydrolysis reaction of the resin occurs resulting in the shortening of its molecular chain. The increase of alkalinity in GFRP attributed to the rising of O-H to C-H chemical bond ratio in the environment leads to the debonding of the fiber and resin. As a result, the resin flows out, and the hydrolysis rate slowly increased first, then accelerated, and finally stabilized.
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