Tensile Behaviour of reinforced ultra-high performance fiber reinforced concrete elements

Ultra-high performance fiber reinforced concrete (UHPFC) is a new class of materials that combine a very strong and dense cementicious matrix with a high fiber content. UHPFC has a very high compressive strength (in the order of 200 MPa) and a relatively large tensile strength (in the order of 10 MPa), along with a strain hardening behavior in tension that ensures that crack openings remain small and provides an enhanced material ductility compared to ordinary concrete. In spite of these advantageous properties, large unreinforced UHPFC members in tension exhibit a brittle behavior at the ultimate limit state, characterized by crack localization and a sudden failure with insufficient structural ductility. To achieve a higher ductility, one possible solution is to add conventional or high-strength reinforcement to the section. The paper presents and discusses some results of an extensive study at the Ecole Polytechnique Fédérale de Lausanne. Tests have been carried out on a series of large-scale unreinforced and reinforced UHPFC specimens, investigating the effect of the amount and type of reinforcement. The specific response of reinforced UHPFC members at cracking is analyzed.