Influence of Hybrid Fiber Reinforcement on Mechanical Properties and Autogenous Shrinkage of an Ecological UHPFRCC

Ultra-high-performance fiber-reinforced cementitious composites UHPFRCC) possess outstanding mechanical properties and durability. Strength development and shrinkage deformation are critical properties of UHPFRCC and should be carefully settled during their application. In this study, hybrid fibers of straight steel fiber (SSF), end-hooked steel fiber (HSF), and cellulose fiber (CF) were used to improve the strength development and reduce the autogenous shrinkage of an ecological UHPFRCC owing to their synergistic effects. Samples with different SSF/HSF ratios, 1:0, 1:1, 2:1, 3:1, 4:1, and 0:1, and with different CF dosages, 0, 0.7, 0.9, and 1.1 kg/m3, were tested. The results implied that the strength development of the UHPFRCC was improved efficiently with the addition of HSF due to its greater bond strength. The compressive strength of the UHPFRCC increased with the increasing ratio of HSF/SSF, achieving its maximum level of 224.8 MPa at HSF/SSF of 1/3 and then decreasing slightly. The addition of CF significantly improved the flexural strength of the UHPFRCC with no compressive strength decline. The internal curing effect of CF inhibited the hydration degree early on and promoted a continuous hydration for a long time. The increased rate of autogenous shrinkage decreased with CF content, and the shrinkage value reduced 33% with the optimal content of CF.