Investigation of the effectiveness of dowels at the interface between reinforced concrete and ultra high performance fiber reinforced concrete

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is a material with unique properties in tension and compression and high energy absorption in the post-cracking region. The superior performance of UHPFRC allows the construction of thin elements with high strength and ductility. A promising application of UHPFRC is for strengthening of existing Reinforced Concrete (RC) structures. In the present study, UHPFRC layers have been applied for the strengthening of full-scale RC beams. For the improvement of the UHPFRC-to-RC interface connection, dowels have been placed in addition to the roughening of surface of the initial beam and the effectiveness of this technique has been evaluated. Flexural tests have been conducted and the interface slips have been recorded in addition to the load-mid span deflections and the load carrying capacity. The results showed that the dowels resulted in better bonding at the interface and delayed the formation of the cracks in the post elastic phase with lower values of slips and subsequent higher load carrying capacity. The main conclusion of this study is that the addition of dowels at the UHPFRC-to-RC interfaces is a technique which should be considered when UHPFRC layers are used for the structural upgrade of existing RC structures