Strengthening effect of concrete beams using ultra-rapid-hardening fiber-reinforced mortar under flexure

In this study, the flexural behavior of concrete beams strengthened with ultra-rapid-hardening fiber-reinforced mortar (URH-FRM) was investigated. The fiber aspect ratio and strengthening thickness were considered as test variables. The results indicated that the tensile performance of the URH-FRM containing polyethylene (PE) fibers with an aspect ratio of 300 or higher was better than that of the URH-FRM comprising fibers with an aspect ratio of 200 or lower. Furthermore, the examined mortar composite achieved a strain energy density of up to 127.2 kJ/m³ at the very early age of 4 h. The results also demonstrated that the flexural performance of concrete beams significantly improved when strengthened with sprayed URH-FRM layer. The flexural toughness of the concrete beams exhibited a greater enhancement as the aspect ratio of PE fibers or the thickness of the strengthening layer increased. The application of sandblasting improved the flexural strength and toughness of the URH-FRM strengthened beams by 48 % and 41 %, respectively, compared with the corresponding values for non-surface-treated beams. In addition, better tensile behavior and strengthening characteristics were imparted to the concrete beams when the URH-FRM layer was hand-casted, instead of being sprayed, and the hand-cast URH-FRM resulted in approximately 11 % higher flexural strength and 15 % higher toughness.