Experimental study on RC beams strengthened in flexure with CFRP-Reinforced UHPC overlays

Abstract

An emerging retrofit technique for bridge decks and other structural members includes attaching field-cast or prefabricated overlays made of ultra-high performance concrete (UHPC). Several studies investigating plain and steel-reinforced UHPC overlays identified two common problems, large thickness leading to high costs and additional dead loads, and localized overlay cracks. To overcome these issues, this work suggests reinforcing the UHPC overlay with carbon fiber reinforced polymer (CFRP) bars. In this study, an experimental campaign is leveraged to evaluate the behaviour of reinforced concrete (RC) beams strengthened in flexure with CFRP-reinforced UHPC overlays. Six beams were tested, including a control, two strengthened with plain overlays with an overlay thickness (t) of 30 or 50 mm, and three strengthened with reinforced overlays using the same two t values above and CFRP reinforcement ratio (ρf-uhp) of 2.1 %, 3.1 %, and 3.9 %. Using plain overlays resulted in an insignificant 8–11 % increase in ultimate load (Pu), with failure being dominated by localized cracking. Beams strengthened with CFRP-reinforced overlays failed in shear, mainly through the concrete beam. For these beams, Pu increased significantly by 179 % to 183 % compared to the control sample, and by 157 % to 159 % compared to plain overlays with same t value. Insignificant behavioral change occurred when varying ρf-uhp from 2.1 % to 3.1 %, likely because the examined ratios are within the optimal ratio which needs to be examined in future research. The CFRP reinforcement also led to significant increase in ductility, 2.34 to 2.63 times that of the control beam. An analytical model was also included and used to predict Pu of strengthened specimens, yielding good match with test results.