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Adding a certain amount of steel fibers can overcome the brittleness defects in geopolymer concrete and improve the mechanical properties, which has a broader application prospect. However, the research on the material properties of steel fiber-reinforced geopolymer concrete (SFGPC) after high temperature exposure is still very limited. Therefore, tests on 114 cubes and 57 prisms after exposure to high temperatures were conducted in this paper. The main variables were temperature (20 °C, 200 °C, 400 °C, 600 °C, and 800 °C), steel fiber volume content (0, 1 %, and 2 %), and concrete type (SFGPC and steel fiber-reinforced ordinary Portland cement concrete (SFOPC)). The results indicated that SFGPC with a steel fiber content of 1 % at 800 °C experienced a 53.6 % reduction in compressive strength, a 58 % reduction in splitting tensile strength, a 93.9 % reduction in elastic modulus, a 45.9 % reduction in toughness index, and a 274.5 % increase in peak strain, compared with room temperature. The 1 % fiber content enhanced the compressive strength by 10.3 %−36.5 %, the splitting tensile strength by more than 16 %, the peak strain by 9.6 %−32.7 %, and the toughness index by 24.4 %−64.6 % compared to the absence of fiber content. Based on the room temperature model, a constitutive model of SFGPC under uniaxial compression after high temperatures was developed. • Cubes and prisms of SFGPC after high temperature exposure were tested. • High temperature reduced the strength, elastic modulus, and toughness index. • Increasing fiber content enhanced the mechanical behavior of SFGPC. • A constitutive model under compression after high temperatures was developed. [ABSTRACT FROM AUTHOR]

Based on the coupling algorithm of smoothed particle hydrodynamics and finite element method, numerical simulation of high-velocity water jet impacting heterogeneous concrete containing aggregates according to the real concrete CT slices was conducted to study the damage evolutions and fracture characteristics of concrete with real structure. The damage evolution and fragmentation process of heterogeneous concrete were obtained, and the fracture characteristic was compared with homogeneous concrete. The internal energy change laws and the damage and stress evolutions in homogeneous and heterogeneous concretes at different time were investigated. And the failure mechanisms of water jet crushing heterogeneous concrete were revealed. The results show that the concrete elements mainly suffer multi-stage plastic damage accumulation failure induced by water jet impact due to stress wave effect, pressured water wedge effect, water flow scouring effect, squeezing effect of aggregate, and stress concentrations. The failures of upper and deep concrete elements are mainly caused by compressive shear stress, which is combined with tensile stress. In homogeneous concrete, the bowl-shaped broken pit with smooth sidewall and the symmetrically distributed cracks are formed. In heterogeneous concrete, the aggregate will prolong the damage accumulation process and lead to the formation of the abnormal broken pit with irregular and rough contour. Cracks prefer to propagate at interface between aggregate and mortar, and concrete elements at interfaces will suffer the sudden brittle failure caused by stress concentration when the damage accumulates to a certain extent. Overall, the internal energy in concrete first rapidly and then slowly increases, and there is a poorer absorption efficiency of jet kinetic energy for heterogeneous concrete, in which the internal energy of aggregates and mortar is closely related to the specific impact object of water jet. The research results would lay the theoretical foundation for water jet efficiently crushing concrete. [Display omitted] • Water jet impacting concrete with actual aggregates was simulated and verified. • Damage evolution and fragmentation process were investigated. • Energy changes and damage-stress evolutions were compared. • Failure mechanisms of heterogeneous concrete were revealed. [ABSTRACT FROM AUTHOR]