Performance Regulation of Low-Hydration, Non-Shrinking, High-Strength Grouting Materials: The Synergistic Effect of GGBS and Expansive Agents

In response to the issues of concentrated early-stage hydration heat and significant self-shrinkage in high-strength cementitious grouting materials at low water-to-binder ratios, improvements were achieved by co-blending granulated blast furnace slag (GGBS) with calcium sulphatoaluminate (UEA) and magnesium oxide (MEA) expansive agents. The workability, mechanical properties, volumetric stability and hydration heat characteristics of the composite system were systematically investigated, and the underlying mechanisms were elucidated through microscopic analysis methods such as XRD, TG and SEM. The results indicate that GGBS improved the fluidity of the pastes and promoted the development of later-stage strength. At the same time, GGBS delayed the peak of hydration heat release and reduced total heat release. In terms of volume deformation, UEA expanded rapidly and exhibited significant compensatory shrinkage in the early stages. MEA expanded slowly in the early stages and displayed more sustained expansion under wet-curing conditions, but experienced significant shrinkage rebound in the later stages under dry environments. Further research revealed that GGBS inhibited the expansion performance of both types of expansive agents. This is primarily attributed to the consumption of Ca(OH)2 within the system, which reduced the alkalinity of the liquid phase. GGBS physically restricted the formation and development of expansion products by promoting the densification of the C–S–H gel.