Producing synchronous grouting material from shield muck with the use of ground granulated blast-furnace slag and carbide sludge

Shield tunneling generates a significant amount of shield muck, which is commonly treated as waste and requires long-distance transport and extensive land occupation for disposal. One potential solution is to utilize shield muck to produce synchronous grouting material, which is required in shield tunnel construction. This study explores the use of industry byproducts, namely ground granulated blast-furnace slag (GGBS) and carbide sludge (CS), in the treatment of shield muck to produce synchronous grout, aiming to enhance treatment efficiency and reduce cost. The strength, consistency, flowability, setting time, and microstructure characteristics of GGBS-CS treated shield muck were examined and compared with those of corresponding ordinary Portland cement (OPC) specimens. Results showed that the optimum strength of GGBS-CS-treated shield muck was 0.86 MPa at 3 days and 3.20 MPa at 28 days, which were 2.5 and 3.2 times higher than that of OPC specimens at these two ages, respectively. In addition, other engineering properties, including consistency, flowability, bleeding rate, and setting time of GGBS-CS-treated shield muck met the standard requirements for synchronous grouting. Microscopic analyses identified the presence of calcium-silicate-hydrate (C-S-H) and ettringite in both GGBS-CSand OPC-treated shield muck, which were generated through binder hydration and pozzolanic reactions of shield muck minerals. Cost analysis indicated that this technique could reduce the construction cost by 279 CNY per cubic meter in the production of synchronous grout. The findings of this research support the reutilization of shield muck in practical shield tunnel projects.