Rheological performance and strength on two component backfilling grout in shield TBM

Ground settlement and segmental displacement during mechanized tunneling require immediate and stable filling of annular gap. Two-component grouts are widely adopted to control gelation and compressive strength. Previous studies suggest that partial replacement of OPC with ground granulated blast-furnace slag (GGBFS) enhances performance, yet the combined effects of cement type and silicate hardener dosage have not been fully clarified. This study investigates the influence of cement type and hardener-to-water (H/W) ratio on rheological, mechanical, and microstructural properties of two-component backfill grouts. Component A is prepared using OPC or plasticized cement (PLC) with bentonite, stabilizer, and deionized water, while Component B is a sodium silicate-based hardener. Rheological properties (bleeding and flow time of Component A, gelation time, plasticity retention time, and flow rate after mixing with Component B) are evaluated along with uniaxial compressive strength (UCS). Microstructural analyses (XRD, SEM, and MIP) examine hydration and pore structure. Results show that PLC exhibits lower bleeding and shorter flow time in Component A, as well as longer gelation time, shorter plasticity retention time, and higher long-term UCS after mixing with Component B compared to OPC. Increasing H/W extends gelation time but shortens plasticity retention time, reduces flow rate, and enhances strength. XRD patterns reveal reduced crystallinity with increasing H/W, accompanied by an intensified amorphous hump at 28°-32°, attributed to the formation of C-S-H gel. Consistently, MIP and SEM confirm the evolution of pore structures as H/W increases, reflecting progressive development of C-S-H gel. These microstructural changes collectively contribute to enhanced compressive strength.