Influence of steel fibers on durability properties of UHPFRC

Ultra-high-performance fiber-reinforced concrete (UHPFRC) is a high-strength cementitious material whose composition can be designed to achieve given properties in the fresh and hardened state. Thanks to the low water/binder ratio (around 0.2) and to the presence of mineral additions, it is characterized by a low porosity which is often taken as a guarantee of intrinsic - almost unlimited - durability. However, the number of researches on the long-term behavior of this type of material is relatively limited, in particular with respect to the corrosion behavior of steel and to the role of steel fibers on concrete durability. This note presents the results of a research aimed at studying the influence of fibers on durability properties. Besides tests for the characterization at fresh and hardened state, durability-related parameters such as electrical resistivity, resistance to chloride penetration, absorption rate and water absorption are investigated. The results show that higher amount of fibers increased the porosity of fibers-concrete interfacial zone and therefore large fibers content negatively influences the parameters related to durability. However, the investigated parameters indicate higher performances with respect to ordinary concretes even in UHPFRC with large fiber content, except for electrical resistivity.