Performance Optimization of Shield Muck-Based Grouting Materials Using Rice Husk Ash and Micro-Expansive Agents

Reusing shield muck in grouting materials offers a sustainable approach to reducing waste from underground construction. However, shield muck-based grouts often exhibit poor workability, early-age shrinkage, and insufficient mechanical performance at high water-to-binder ratios. This study investigated the effects of rice husk ash (RHA) and micro-expansive agents on the workability, early-age deformation, mechanical properties, and hydration characteristics of shield muck-based grouting materials. The influences of RHA substitution rate, water-to-binder ratio, muck particle size, and expansive agent type and dosage were evaluated through macroscopic and microstructural tests. The incorporation of RHA reduced the consistency value and setting time by 12.5–27.5% and 31.5–39.9%, respectively. The combined use of RHA and a micro-expansive agent further improved early-age volumetric stability. Compared with the unmodified reference mixture R0W2.4M, the volume shrinkage ratio of the modified mixture was reduced by 78.2%. The mechanical performance depended on the RHA substitution rate and expansive agent dosage. Among the investigated mixtures, the mixture with a water-to-binder ratio of 2.6, 25% RHA, large particle size shield muck, and an appropriate expansive agent dosage showed favorable overall performance. The results demonstrate that RHA and micro-expansive agents can effectively mitigate shrinkage and improve the engineering performance of shield muck-based grouting materials.