Durability of GFRP Bars under Compression with Different Length-to-Diameter Ratios Exposed to a Simulated Concrete Environment

There is increasing interest in using glass fiber–reinforced polymer (GFRP) bars for reinforcement in compressive members such as concrete columns and bridge piers. However, the understanding of their long-term compression performance in an alkaline environment remains unknown. This study investigated the durability under compression of 12.7-mm-diameter GFRP bars with different length-to-diameter ratios (4, 8, and 16) by exposing them to an alkaline solution with a pH of 12.5–13.0, simulating the surrounding concrete environment. The effect of exposure temperature (23°C, 60°C, and 80°C) and exposure duration (42, 83, and 125 days) was evaluated. The results show that the retained compressive strength of GFRP bars after exposure to a simulated concrete environment varied with length-to-diameter ratios. The degradation of the resin-rich outer surface significantly impacted the compressive strength of the GFRP bars with length-to-diameter ratios of 4 and 8 because their failure mode of fiber crushing initiated from the bar surface. The GFRP bars with a length-to-diameter ratio of 16 failed by fiber-splitting mode under buckling, initiated from inside the bar, and their compressive strength was similar to that of unexposed GFRP bars. Analysis further revealed that temperature and exposure duration were statistically significant, affecting the compressive strength of the GFRP bars with length-to-diameter ratios of 4 and 8, but not those with a length-to-diameter ratio of 16. This study provides a detailed understanding of the durability of GFRP bars under compression, which will be useful in their effective design as longitudinal reinforcement in concrete structures.