Mixture design of self-levelling ultra-high performance FRC

Abstract

Fibre reinforced concrete (FRC) generally has low workability, especially when the water/cementitious materials (W/CM) ratio is low and the fibre content is high. Hence, the production of self-levelling ultra-high performance FRC is rather difficult. Adding more superplasticizer (SP) may be one solution, but there could be the problem of over-dosage. In this research, the fresh and hardened properties of FRC containing different amounts of steel fibres were studied. To achieve ultra-high performance, the W/CM ratio was lowered to 0.17 and the fibre volume was increased to 2%. The workability was evaluated in terms of slump, flow, flow rate and a newly defined measure called degree of levelling, whereas the strength was evaluated in terms of cube strength. It was found that there is an optimum SP dosage for maximum degree of levelling. Moreover, by correlating the strength of the FRC to the plain matrix strength and fibre volume, design equations were derived from which it can be seen that the matrix strength and fibre volume are the key factors governing the strength of FRC and that they together exert certain synergistic effect.