Effect of High Plasticiser Dosage on Ultra High-Performance Fibre Reinforced Concrete (UHPFRC)

The overall objective of this study was to develop an optimised UHPFRC matrix based on the modified Andreasen and Andersen optimum particle packing model by using available South African materials. The focus of this study was to determine the optimum combined fibre and superplasticiser content for UHPC by using a response surface design. The UHPFRC was appropriately designed, produced and tested. The flowability, density and mechanical properties of the designed UHPFRC were measured and analysed. It is clear from the results, that both the fibre and superplasticiser content play a significant role in the flowability of the fresh concrete. The addition of fibres significantly improved both the compressive and indirect tensile strength of the UHPFRC. However, the addition of superplasticiser slightly decreased both the compressive and indirect tensile strength of the UHPFRC. Both the fibre and superplasticiser content had an insignificant effect on the modulus of elasticity. The results show that the superplasticiser content can be increased if a more workable mix is required without decreasing the strength significantly. The study demonstrate that it is possible to efficiently produce a dense and workable UHPFRC with relatively low binder amount and low fibre content. This can result in more cost-effective UHPFRC, thus improving the practical application thereof.