Mechanical characterisation of the stiffness and strength of ultra-high-performance fiber-reinforced concrete (UHPFRC)

Abstract Ultra-high-performance fibre-reinforced concrete (UHPFRC) is a new material developed to present superior properties, such as high uniaxial compressive strength (superior to 100 MPa), high durability, low permeability and satisfactory ductile behaviour. This paper presents the mechanical characterisation of UHPFRC and compares it with a reference mixture of reactive powder concrete (RPC). The mechanical characterisation consisted in obtaining the following properties: compressive strength at 28 days (fc,28), static elastic modulus (Eci), toughness (T) and dynamic elastic modulus (Ed). UHPFRC presented 20% and 51% gain of strength and toughness, in relation of RPC. Nevertheless, the stiffness values (i.e., Eci and Ed) were very similar to RPC. This behaviour is explained by the fact that steel fibres are not activated at low levels of stress, however, at higher loads, the toughness increases in UHPFRC samples. Furthermore, Ed were monitored up to 365 days, and there was considerable gain in stiffness over time, mainly due the addition of silica fume. Furthermore, a constitutive compression law was obtained for UHPFRC and RPC, with R2 = 0,992.