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

Abstract

This study aimed to prevent water flow in microcracks and simultaneously achieve CO2capture 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 CO2injection at 2 MPa. Through CO2dissolution, 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 SO42-) 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 CO2solubility, 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 SO42-ions. Microcracks grouted with CCG extended the CO2utilization 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.