Effect of design parameters on the properties of ultra-high performance fibre-reinforced concrete in the fresh state

International audienceThe properties of Ultra-High Performance Fibre-Reinforced Concrete (UHPFRC) in the fresh state were studied and analysed. The design parameters were the nature of the mineral admixture (metakaolin or silica fume), the fibre content and the paste content. Workability tests (mini slump-flow and mini L-box) were carried out immediately after mixing and after different resting times. Rheological tests were performed in order to evaluate the shear-dependent properties as well as the time-dependent ones. Workability results showed that the self-compacting ability targeted at the end of mixing was maintained up to 20 min after mixing for all UHPFRCs. Highlighting some significant relationships between workability measurements and rheological parameters enabled the flow properties to be analysed depending on the mixture composition. In particular, at given fibre and paste contents, UHPFRC incorporating metakaolin displayed higher plastic viscosity and structuration rate than UHPFRC containing silica fume. Furthermore, even if designed with lower fibre content or lower paste content, UHPFRC made with metakaolin was always more thixotropic than UHPFRC with silica fume. For the case of UHPFRC, having the highest metakaolin and fibre contents, a practical solution is proposed to prevent distinct-layer casting from occurring in the precast factory