Accelerator for Concrete and Consolidation
Sodium silicate is widely used in tunnel construction as an accelerator for concrete. After excavation, the tunnel’s internal walls are coated using the shotcrete technique (sprayed concrete). The silicate, mixed directly in the spraying nozzle of the concrete, promotes the immediate setting of the cement, allowing for the application of multiple layers of concrete with considerable thickness.
Consolidation
Before proceeding with tunnel excavation, it is sometimes necessary to consolidate the ground. In simpler cases, cement slurries are used, but when there are issues such as very small voids or the presence of groundwater, ‘chemical injection’ is employed.
The injected products are based on sodium silicates and allow for soil consolidation and water impermeability, thanks to the formation of silica gel that strengthens and seals the ground. The method to obtain the gel varies; one technique is the Toosten process, which uses separate injections of sodium silicate in solution followed by a reagent like calcium chloride, which reacts to instantly form a gel. Alternatively, the gel time can be controlled by adding a slow-reacting reagent, which is pre-mixed with the silicate and then injected.
Some co-reagents include sodium carbonate, sodium aluminate, or organic esters. The high degree of formulation flexibility of the silicate undoubtedly represents a significant advantage during the application phase.