At present, sprayed concrete has problems such as low strength, large rebound amount, and high dust concentration. Developed a new type of alkali-free liquid accelerator, which can effectively improve the performance of shotcrete. The alkali-free liquid accelerator is mainly composed of aluminum sulfate, active aluminum hydroxide, alcohol amine, amide, and stabilizer. Through laboratory tests and field tests, when the alkali-free liquid accelerator admixture is 5% to 7%, the initial setting time is within 5 minutes, and the final setting time is within 10 minutes. The strength of shotcrete reaches 12.8MPa in one day, and the compressive strength ratio of 28d is more than 95.3%, and the rebound amount is within 10%. Compared with ordinary alkali-free liquid accelerator and alkaline liquid accelerator, the strength of sprayed concrete mixed with the alkali-free liquid accelerator is greatly improved, which is more conducive to the support of the sprayed layer, reduced rebound and dust, effectively improve the construction environment and increase construction efficiency.

No abstract

Waste sediment (WS) is a solid waste produced from subway construction. In the present work, high-volume WS was upcycled to prepare grouting material.The results showed that the working performances (consistency, fluidity, setting time, bleeding ratio, and stone ratio)of WS-based grouting material were significantly affected by the mass concentration of solid components, binder to WS ratio, and steel slag addition. This material can meet the engineering requirement by adjusting these parameters. The WS-based grouting material exhibited superior performance compared to traditional grouting materials. It achieved self-leveling (160 mm fluidity) and wassuitable for grouting (consistency within 100-130 mm, 95.0% stone ratio). Amorphous phases were formed in the hardened sample. The addition of a suitable amount of steel slag (10%) can reduce the total porosity, and also promote the hydration degree and increase the mechanical properties of cement matrix.The strength development can be attributed to the formation of hydration products and the cementation between hydrates and sediment particles.