Microstructural investigation of glass fiber reinforced polymer bars

Microstructural characteristics are crucial in understanding and predicting the behavior of glass fiber reinforced polymer (GFRP) bars used for concrete reinforcement. Considering the lack of extensive GFRP microstructural knowledge, the main purpose of this study is to provide a documentation of GFRP microstructure and demonstrate its contribution in the durability of GFRP bars. Scanning electron microscopy (SEM) imaging was performed at different magnification levels on the cross-section of four different commercially available pristine GFRP bars. As a result of differences in the production method by pultrusion, each pristine bar presented a unique microstructural pattern including voids, defects, and fiber distribution. Two of the bars which demonstrated the most different patterns were exposed to accelerated conditioning in alkaline solution. The horizontal shear test was performed and the results were compared with the pristine bars. The difference in microstructural patterns was found to significantly contribute to GFRP durability. These results can be used as a benchmark for the microstructure of commercially available pristine GFRP bars and serve as a base for monitoring possible changes after any conditioning or testing.