Development of sustainable tail grout through the utilization of shield muck and waste-activated ground granulated blast furnace slag

Abstract

A huge amount of shield muck is generated during shield tunneling, and the reutilization of shield muck to produce tail grout has attracted growing attention, aiming to mitigate the environmental issues related to the transport and disposal of shield muck. However, conventional binders, such as cement, used in this technique are associated with high carbon emission. Therefore, this study investigates the use of low-carbon binder, i.e., carbide sludge (CS)-activated ground granulated blast furnace slag (GGBS), in shield muck treatment, aiming to achieve sustainable reutilization. Various commercial additives and phosphogypsum (PG), an industry waste, were added to further enhance the properties of treated shield muck. Results show that incorporating sulfate-containing additives to GGBS-CS-stabilized shield muck significantly reduced the setting time from 26.75 to 8.00–12.00 h, with Na₂SO₄ and PG showing a relatively higher reducing rate. In addition, adding Na₂SO₄ and PG to GGBS-CS-stabilized shield muck could enhance the 3-day strength by 67.0% and 37.0%, respectively, while their effects on improving the 28-day strength were marginal, yielding increases of just 16.0% and 0.4%. Results also indicated that additives led to a higher stone shrinkage rate of grout. Nonetheless, all additives posed negligible effects on the consistency and flowability. Microstructure analysis indicated that additives promoted the generation of ettringite (AFt) and aluminate ferrite monosulfate (AFm) phases. These phases consume free water and refine pores, leading to the higher stone shrinkage rate. Isothermal titration calorimetry highlighted that the additives affect the heat rate in the time interval of 4–50 h after mixing, and this should be the reason for the significant influence of additives on setting time and 3-day strength as well as limited impact on consistency and flowability. The findings confirmed the feasibility of using stabilized shield muck to produce tail grout, and PG is efficient in further enhancing its properties.

Graphical Abstract