Influence of Manufactured Sand Gradation and Chloride‐Free Alkali‐Free Accelerator (CFAFA) on the Performance of Shotcrete

Aiming at the deficiencies in the design of the proportion of the mechanism sand shotcrete, this study systematically investigated the influence of mechanism sand gradation and stone powder content on the working performance, mechanical properties, and durability of shotcrete, combined with microanalysis, revealing the synergistic mechanism of chlorine‐free alkali‐free quick‐setting agent and stone powder. The results show that when the proportion of coarse particles larger than 1.18 mm in the gradation of mechanized sand is more than 35%, the fluidity of concrete decreases significantly, while the proportion of fine particles smaller than 0.3 mm is higher than 30%, which will lead to an increase in the viscosity; the working performance of the stone powder is the best when it is mixed in 8%~16%. The compressive strength is positively correlated with the working performance of concrete, and the 28‐day strength of the best‐graded group reaches 42.5 MPa; when the dosage of stone powder is less than 12%, the strength is improved with the increase of dosage. Compared with ordinary quick‐setting agent, the optimal composite system (12% stone powder with chloride‐free alkali‐free accelerator [CFAFA]) dramatically reduced the penetration height by 83.3% (from 36 to 6 mm), the mass loss rate under freeze–thaw cycles is reduced by 39.5%, the relative kinetic elastic modulus is increased by 8.8%, and the corrosion resistance coefficient is increased by 5.7% at the dosage of 12% of stone powder. The micromechanism shows that under the nucleation of stone powder, the CFAFA catalyzes the early formation of hydration products such as calcite, ettringite (AFt), and calcium silicate hydrate (C‐S‐H) gel. In the later stage, the CaCO 3 in the stone powder participates in the hydration reaction to form a dense “calcite‐calcium aluminate carbonate‐C‐S‐H” three‐phase system, which plays a role in filling pores and enhancing long‐term stability. The research results provide a theoretical basis for the design of grading, selection of accelerator, and resource utilization of mechanism sand and stone powder in tunnel engineering, which can significantly improve the quality of the project and reduce the cost.