In this paper, the degradation mechanisms of pultruded fiber-reinforced polymer (FRP) composites with various types of fibers and polymer matrices, including basalt, carbon, and glass fibers, as well as amine-cured and anhydride-cured epoxy matrices, styrene-cured vinyl ester matrices, and unsaturated polyester matrices, are summarized under corrosive environments. Then, the damage mechanisms of the components of pultruded FRP composites are classified into three groups, including chemical etching & leaching, hydrolysis, and physical degradation. Additionally, a generally degradation model, the hydroxyl ions diffusion-based model (HIDM), is proposed and validated using extensive test data, demonstrating good accuracy and wide applicability for pultruded FRP composites with various cross-sectional shapes. The structural safety of FRP-reinforced concrete structures will be significantly weakened when the damage depth became greater than 6% diameter of FRP bars, corresponding to a strength retention of 77.4%. Furthermore, a new bond failure criterion for pultruded FRP bars used in construction, damage depth level, is proposed to evaluate the premature deterioration and functional obsolescence of FRP-reinforced concrete structures, which could provide a unique perspective and insight for structural safety assessment.
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