In this study the efficiency of the use of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) for the strengthening of existing Reinforced Concrete (RC) beams has been investigated. Experimental work has been conducted to determine UHPFRC material properties. Dog-bone shaped specimens have been tested under direct tensile loading, and standard cubes have been tested in compression. These results have been used for the development of a numerical model using Finite Element Method. The reliability of the numerical model has been validated using further experimental results of UHPFRC layers tested under flexural loading. Further numerical study has been conducted on full-scale beams strengthened with UHPFRC layers and jackets, and these results were compared to respective results of beams strengthened with conventional RC layers and with combination of UHPFRC and steel reinforcing bars. Superior performance was observed for strengthened beams with UHPFRC three side jackets, and the efficiency of this technique was highlighted by comparisons with other strengthening techniques.

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Ultra-High Performance Fibre Reinforced Concrete is a material which is becoming increasingly popular in structural applications, mainly due to its superior mechanical characteristics. The mechanical properties of this material are of high importance and the development of non-destructive techniques is vital for the evaluation of the mechanical characteristics of existing structures. In the current study, Ultra-High Performance Fibre Reinforced Concrete with different amounts of steel fibres has been examined. Compressive and tensile tests have been conducted alongside with Ultrasonic Pulse Velocity and Rebound Hammer measurements and the development of appropriate empirical non-destructive models has been examined.

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Ultra high performance fiber reinforced concrete (UHPFRC) is a concrete type with superior mechanical properties and of a relatively high tensile strength. The tensile stress–strain characteristics of UHPFRC are highly affected by the mixture design and the curing regime. In this study, an extensive experimental investigation has been conducted with direct tensile tests on a number of specimens that contained different percentages of steel fibers and different cement types were applied. Also, various curing regimes were investigated. Different models depending on the steel fiber amount were proposed for the simulation of the stress–strain and the stress‐crack opening response of UHPFRC, while the fracture energy was also calculated for the different fiber contents. Finally, the effect of fiber content and curing time on the variation of the experimental results are discussed.