Energy evolution and damage-failure characteristics of FACs UHPC under cyclic loading

In order to reveal the influence mechanism of fly ash cenospheres on energy dissipation and damage evolution path of UHPC under cyclic loading, the fly ash cenospheres-UHPC mix ratio was optimized through orthogonal experiments, and its mechanical properties under uniaxial compression and cyclic loading and unloading were analyzed. The results show that: 1) The water-cement ratio and steel fiber content had the greatest influence on the fluidity and compressive strength of UHPC mixtures, respectively. Furthermore, the addition of fly ash cenospheres also improved the fluidity of UHPC. Through range analysis on compressive strength and fluidity indices, the optimal mix proportion (A3B4C2D2) was determined. 2)The residual stress in preferred group (20 cycles) under cyclic compression load was 55.8% of peak stress, which was greater than that in control group (33.5%). Meanwhile, the control group and the preferred group reached the peak load after 10 and 13 cycles, respectively, which reflected that the preferred group of specimens had a better ductility. 3) Under the action of external load, the synergistic effect of fly ash cenospheres crushing and subsequent crack propagation significantly absorbed substantial energy, thereby delaying structural failure. The crack-blocking synergy between fly ash cenospheres and fibers further enhanced energy consumed by crack propagation, that is, effectively mitigating the brittle failure mode of UHPC.