Study on the fluidity of foamed alkali-activated slag cementitious material (AASCM).

This study aims to investigate the evolution patterns of fluidity and rheological properties of AASCM under varying dosages of foaming agent and particle sizes of filling aggregate. The flow characteristics of AASCM are significantly affected by the filling aggregate's size and the foaming agent's dosage. Specifically, an increase in filling aggregate size (D(4,3) ϵ [26 µm, 69 µm]) enhances the fluidity of foamed AASCM, while an increase in foaming agent dosage reduces fluidity. These observed variations can be attributed to the presence of particle voids, the specific surface area of the aggregate, as well as the quantity and spatial distribution of bubbles within the slurry. A bubble-particle packing model is established, and by calibrating the simulation error coefficient to 1.1, the study investigates the evolution of water film thickness (WFT) in foamed AASCM with slurry expansion degree. It is observed that bubbles in the slurry affect the fluidity by altering the overall compactness and specific surface area of the foamed slurry, subsequently modifying the WFT.

Experimental Investigation of CO2-Induced Silica Gel as the Water Blocking Grout Effect of Aquifer Ions.

This study aimed to prevent water flow in microcracks and simultaneously achieve CO2 capture during grouting (CCG). Using sodium silicate (SS) as the primary material, the microcracks were grouted by a two-step approach. The low-initial-viscosity (5 mPa s) SS was first saturated within the microcracks followed by CO2 injection at 2 MPa. Through CO2 dissolution, silica gel was developed and tolerated a hydraulic pressure of up to 5.5 MPa. The effects of aquifer ions (Na+, Ca2+, Mg2+, HCO3 -, and SO4 2-) were equally evaluated at harsh conditions, and it was found that the strength of the silica gel was reduced, which was caused by salting out, low CO2 solubility, and precipitation. As a result, the hydraulic pressure was reduced to as low as 3 MPa. After 210 days, 16% of the silica gels (without ion inclusion) were reversible to the liquid phase, where a similar effect was found in the cases of Na+ and Mg2+ ions. The degradation increased with more Ca2+ ions (up to 55%) and decreased with more HCO3 - and SO4 2- ions. Microcracks grouted with CCG extended the CO2 utilization in grouting application. Combined with the effect of dissolved ions, the proposed approach is feasible in the field implementation for underground engineering under water bodies.