Functionally graded ultra-high performance cementitious composite with enhanced impact properties

This study develops functionally graded ultra-high performance cementitious composite beams by applying the composite concepts of Ultra-high Performance Concrete (UHPC), Two-stage Concrete (TSC) and Slurry-infiltrated Fibrous Concrete (SIFCON). The functionally graded composite beam (FGCB) is fabricated with a bottom layer of SIFCON and top layer of TSC, and the two layers are synchronously cast by using UHPC slurry. The novel concept of FGCB is proposed towards more economical and high performance structural systems, namely excellent flexural bearing capacity and impact resistance, low cement consumption and high steel fibre utilization efficiency. The fresh and hardened properties of UHPC slurry, flexural and impact properties of FGCB are measured. The results reveal that the designed FGCB has superior flexural properties and impact resistance, without showing any interfacial bond problem. The fibre utilization efficiency of the designed FGCB is very high compared to the traditional UHPC and SIFCON beams. The 30 mm medium hook-ended steel fibres show the best utilization efficiency compared to the 13 mm short straight and 60 mm long 5D steel fibres, and 3% medium fibres are optimum to design FGCB. The low-velocity impact resistance of FGCB is well linearly correlated with its static flexural toughness.