Preparation and engineering properties of alkali-activated filling grouts for shield tunnel

Abstract Alkali-activated materials (AAM) have attracted extension attention as a promising alternative to ordinary Portland cement (OPC) in many applications. Back-fill grouting is a key procedure in shield tunnel construction. In view of the deficiency of traditional OPC-based grout in consuming natural resources and polluting the environment, it is of great significance to develop low carbon and environmentally friendly alkali-activated grouts (AAG). In this study, AAG used for back-fill grouting in shield tunnels were prepared with fly ash, ground granulated blast-furnace slag and steel slag as the main cementitious materials, supplemented by fine sand and additive. Through laboratory tests, the effects of factors including the concentration of the alkaline activator solution and liquid-to-solid ratio on the performance of AAG were studied systematically. Moreover, the performance of AAG was analyzed and evaluated in terms of basic physical properties, working properties, hardening properties and pore structure properties, and two representative groups of AAG (AAG-Ⅰ and AAG-Ⅱ) were recommended by comparing with a typical OPC-based grout. The results show that the setting time, fluidity and its loss rate over time of AAG can be adjusted in a wide range, and AAG can be flexibly selected for use according to the requirements of grout performance for specific construction cases. By adjusting the ratio parameters of AAG, the 28-day underwater/in-air strength ratio and impermeability pressure of AAG can reach over 0.80 and 0.8 MPa, respectively, showing excellent water dispersion resistance and impermeable performance, while AAG have excellent working properties. Compared with the typical OPC-based grout, AAG-Ⅰ shows better engineering performance.