Flexural performance of reinforced concrete (RC) beam strengthened by UHPC layer

Reinforced concrete (RC) structures may be subjected to an increase in load, severe environmental attack, and other factors that may lead to deterioration. Strengthening/repair techniques are typically used to upgrade the strength or enhance the durability, which extends the service life of the structures. In the current study, the behavior of reinforced concrete beam strengthening by the UHPC layer with/without construction joints were investigated. Seven RC beams were examined in the current experimental program. The variables were the continuity of the UHPC layer, the location of the construction joint and the type of the reinforcement across the joint. One beam was used as control without any UHPC overlay. The effect of the steel/GFRP bars across the construction joints was also performed and the results were compared with control specimens. The results indicate that the inclusion of UHPC layers at the tensile side of the RC beams significantly increased their stiffness (20–132 %) and delayed the crack initiation. Meanwhile, the presence of the construction joint in the UHPC overlay decreased the efficiency of the strengthening method. Furthermore, utilizing steel /GFRP bar in UHPC overlay across the construction joints showed a significant increase in loading carrying capacity (17.15–41.1 kN) and had a significant effect on the modes of failure. The results also demonstrated that the UHPC overlay experienced a sufficient bond to concrete as no separation was observed.