Shear strengthening of reinforced concrete beams using geopolymer-bonded small-diameter FRP bars

In this study, a comprehensive investigation of the shear behavior of RC beams strengthened with a small-diameter FRP bar-reinforced geopolymer matrix (FRGM) system is presented for the first time. A total of twelve RC beams, including two reference beams and ten strengthened beams, were prepared and tested. Five factors were considered, including bonding methods (geopolymer-bonded vs. epoxy-bonded), matrix types (slag-to-fly ash ratios of 9:1 vs. 6:4), alignment directions of small-diameter FRP bars (90° vs. 45° to the longitudinal direction), configurations of FRGM layers (single-side vs. double-side), and shear span-to-depth ratios of RC beams (a/d = 2.4 vs. 3.2). The strengthening efficiency of RC beams with the double-side FRGM layer (1.9 times that of the reference beam) was found to be much larger than that of the RC beams with the single-side FRGM layer (1.2 times that of the reference beam). In addition, the geopolymer-bonded layer showed a similar load capacity (approximately 98 %) to its epoxy-bonded counterpart. The use of steel fibers in geopolymer matrix further restrained the development of shear cracks and improved the shear capacity. Finally, a theoretical analysis method was proposed for predicting the shear capacity of the FRGM-strengthened RC beams.