Fibrous geopolymer paste composites for near-surface-mounted strengthening of reinforced concrete beams in flexure

Strengthening for buildings is considered a promising technique in civil engineering, as the buildings may be exposed to various factors that make strengthening a necessity. One of the most important strengthening techniques is the near-surface mounted (NSM) technique. This study includes casting and testing fourteen reinforced concrete (RC) beams having dimensions of 200 × 125 × 1050 mm. The variables include fiber types in geopolymer paste adhesive, materials of NSM-bar, and the number of grooves. Two specimens are the control beams (without strengthening) and the remaining twelve specimens are NSM-strengthened and divided into two groups. The first group has six RC beams strengthened by NSM-steel bars (diameter 8 mm) and the second group has six RC beams strengthened by NSM-glass fiber-reinforced polymer (GFRP) bars (diameter 6 mm). Each group consists of three specimens having a single NSM-groove, and the other three specimens have double NSM-grooves. The adhesives used are a geopolymer paste adhesive, with three types of fibers (micro steel fiber, carbon fiber and, polypropylene fiber). The key test results include the ultimate load capacity, load-deflection behavior, characteristics of the cracks, and the strain at the concrete and the bars. A clear improvement in the characteristics of the RC beams is seen in the results when strengthened by the NSM-technique compared to the control RC beam. The specimens strengthened by two NSM-steel bars with carbon fiber geopolymer paste adhesive give the best results, where the increase of the first crack and ultimate loads are equal to 70.0 % and 61.7 %, respectively, compared to the control RC beam. Then the ultimate flexural capacity of the strengthened beams is analysed using ACI 440.2R-19 [1], the ratio of the experimental to the predicted moment ranges from 0.99 % to 1.15 %.