A novel micromechanical model of residual fracture energy of hooked-end steel fiber reinforced concrete exposed to high temperature

Abstract It remains challenging to quantitatively describe the relationship between the incorporation of fibers and the residual fracture energy of hooked-end steel fiber reinforced concrete (HSFRC) exposed to high temperature. The residual fracture energy contributed by the hooked-end steel fiber is classified into two types: (i) the energy consumed by frictions including the fiber sliding friction, the Coulomb friction at the hook corner, and the friction induced by the fractured matrix; (ii) the deformation energy by straightening the hooked ends. Based on the pullout energy of the single fiber, we develop a micromechanical model to predict the residual fracture energy of HSFRC considering the thermal deterioration of the cementitious matrix and the steel fiber exposed to temperature levels ranging from 20 ˚C to 800 ˚C. This novel micromechanical model, validated by previously published experimental data, is then utilized to study the effects of the fiber length, diameter, volume fraction, and the yielding tensile strength and the matrix type upon the residual fracture energy of HSFRC. Interestingly, we find that tuning the fiber length, diameter, and volume fraction can achieve more remarkable improvements in the fire resistance of HSFRC than regulating the initial yielding tensile strength of steel fibers and the matrix type. Our micromechanical model could, therefore, enable the computational optimal design of fire-resistant HSFRC.