Bar size effect on long-term durability of sand-coated basalt-FRP composite bars

Recently, the use of basalt fiber-reinforced polymer (BFRP) bars as a reinforcing material has gained increasing interest worldwide. In the last decade, the durability of BFRP bars has been the concern of the researchers, however, the effect of bar size or diameter have not yet been addressed. This paper investigates the effect of bar size on the physical, mechanical, and durability characteristics of newly developed sand coated BFRP bars conditioned for 3 months at 60 degrees C in an alkaline solution simulating a concrete environment. Five diameters of BFRP bars (nominal diameters of 9.5, 13 mm, 12.7 mm, 15.9 mm, 19.0 mm, and 25.0 mm) were investigated before and after conditioning. In addition, the microstructure of the BFRP bars-both conditioned and unconditioned specimens-was investigated with scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) to assess any changes or degradation. The results revealed that the physical and mechanical properties of the reference BFRP bars were significantly affected by the cross-sectional size of the bar. The higher probability of defects contained in the larger diameter bars may have caused the lower interlaminar and transverse shear strength, and flexural strength in comparison to the smaller diameter bars. On the other hand, the conditioning in the alkaline solution had a greater negative effect on the mechanical properties of the larger BFRP bars than on the smaller ones. According to the finding of this research, there were variations between the physical and mechanical properties of the BFRB bars of different diameters.