Shotcrete is widely used in civil engineering as a supporting structure. In this paper, the compressive behavior of ultra-high-performance shotcrete (UHPSC) with different steel fiber content by volume (0, 0.5%, 0.75%, 1%, 1.25%, 1.5%) was investigated. The results showed that the failure pattern of UHPSC was changed from brittle failure to ductile failure with the increase in steel fiber content. The compressive strength, peak strain and compressive toughness of UHPSC increased with the increase in steel fiber content, but the elastic modulus and Poisson’s ratio did not change significantly. With content of 1.5% steel fibers, its axial compressive strength, peak strain and compressive strain energy were 122.7 MPa, 3749 με and 0.269 MPa, respectively, increased by 14%, 23.5% and 55.5% compared with those without steel fiber. The peak strain and compressive toughness were higher than that of ultra-high-performance concrete (UHPC), while the elastic modulus of UHPSC was lower than that of UHPC. Based on the experimental data, the relationship between compressive strength, peak strain, compressive toughness and the change in the characteristic value of steel fiber content (λ_f) were revealed. The uniaxial compressive constitutive model of UHPSC with different steel fiber content was established and reflected the change rule of the shape parameter of α (constitutive model ascending section) and β (constitutive model descending section) with λ_f. The experimental results were in good agreement with the model calculation results, which can provide theoretical support for the structural design of UHPSC.

Shotcrete is widely used in mine and civil engineering as supporting structure. A new type of ultra-high-strength shotcrete (UHSSC) with viscosity-enhancing agent was taken as the research object in this paper. A microstructure model of UHSSC under different curing conditions (standard curing, natural curing and film curing) was reconstructed using X-ray computed tomography (X-CT). The grey theory was used to analyze the correlation between pore characteristics and strength of UHSSC. The results showed that the porosity and the pore size of UHSSC were significantly reduced, the compressive strength was obviously improved by the new spraying process. The effects of curing conditions on the pore characteristics and compressive strength of UHSSC were obvious. Under natural curing, the hydration degree was the highest, the maximum pore size was the smallest, and the compressive strength was the highest, reaching 95.8 MPa, but the porosity was the highest. The curing condition had a certain influence on the sphericity distribution of UHSSC pores. Under film curing, the proportion of special-shaped pores (S < 0.4) was the largest and compressive strength was the smallest. There was a good correlation between pore characteristic parameters and the compressive strength of UHSSC under different curing conditions. In particular, the large pore size (D ≥ 5000 µm) and special-shaped pores (S < 0.4) had obvious effects on the strength of UHSSC, and the grey correlation coefficients were 0.8539 and 0.8080, respectively. Additionally, the pore direction of UHSSC had obvious directionality, and the anisotropy of UHSSC may be more prominent than poured specimen. The results will lay a foundation for the study of its mechanical properties and durability.

Shotcrete is widely used in mine and civil engineering as supporting structure. A new type of high-performance shotcrete (HPSC) with thickener has been taken as the research object in this paper. In order to quantitatively analysis the pore structure characteristics of the HPSC, microstructural model in 3D was reconstructed by X-ray computed tomography (X-CT) technology. The internal relationship between compressive strength and pore structure parameters of HPSC was revealed and discussed. The porosity of HPSC was reduced significantly and the material was more compact, compared with the poured specimen of the same proportion. The compressive strength of HPSC increased by 38.9% on average, and the maximum compressive strength was 96.9MPa. The sphericity of pores was closely related to the pore size, and the larger the pore size was, the smaller the sphericity was. The sphericity of the large pores was reduced by the spraying process, making the morphology of the large pores more complex and more sensitive to stress. Additionally, the pore direction of shotcrete had obvious directionality, and the anisotropy of shotcrete will be more prominent than poured specimen. The results will lay foundation for the study of its mechanical properties and durability.