Structural Response of Elements Combining Ultrahigh-Performance Fiber-Reinforced Concretes and Reinforced Concrete

The use of ultrahigh-performance fiber-reinforced concretes (UHPFRC) improves the structural response and extends the durability of concrete structures. Three basic configurations for structural elements combining UHPFRC and reinforced normal strength concrete are proposed with regard to typical demands on rehabilitation projects. They fulfill a protection function and the resistance can be increased if required. The flexural response of these composite UHPFRC–concrete elements is investigated with an original analytical cross-sectional model in a parametric study: UHPFRC increase stiffness and resistance and delay the formation of localized cracks. For this, a minimum magnitude of strain-hardening of 0.2% is necessary. Additional reinforcement in the UHPFRC layer is the most efficient way to increase the bending resistance. The investigation demonstrates how to use UHPFRC and reinforcing bars best in rehabilitation of existing concrete structures.