A recent study has revealed a major advancement in sustainable construction materials. Researchers have developed a new grout—colloidal silica recovered from geothermal fluids (CSRGF)—that significantly enhances soil stability and liquefaction resistance while offering a lower environmental footprint. This material could be a game-changer for infrastructure projects, particularly in earthquake-prone regions where soil reinforcement is critical.
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Background
Chemical grouting is a widely used soil stabilization technique that involves injecting a gel-forming chemical grout into the ground through underground pipes. This process replaces pore water, helping to control water flow and strengthen the soil, making it essential for construction and infrastructure maintenance.
Traditional waterglass-based chemical grouts are effective at improving soil permeability and stability. However, they have significant drawbacks, including groundwater contamination due to leachate and limited durability in varying environmental conditions. While colloidal silica and other advanced chemical grouts provide some improvements, they also come with environmental concerns.
This study introduces CSRGF, a novel, carbon-neutral grout developed using silica extracted from geothermal fluids—a byproduct of geothermal energy production. By incorporating colloidal silica with water glass, this formulation aims to enhance mechanical durability while reducing CO2 emissions compared to conventional silica-based grouts.
Methods
For this study, the CSRGF grout was formulated using an optimized mix of colloidal silica, water glass, reagents, and buffers. The researchers measured its viscosity immediately after mixing and tracked changes up to the setting point. The gel structure of CSRGF was further analyzed using small-angle X-ray scattering (SAXS) on a 28-day-old sample.
To assess long-term durability, the team conducted unconfined compressive strength tests after 300 days, evaluated liquefaction resistance, and analyzed silica leaching. Hydrogel specimens of CSRGF grout were also examined for volumetric shrinkage using glass capillaries to simulate the pore space of coarse sand. These samples were cured at temperatures ranging from 20 °C to 60 °C for up to 28 days.
Liquefaction resistance was tested using silica sand grout specimens under simulated seismic conditions. Additionally, cyclic triaxial tests were performed on sand-gel specimens reinforced with CSRGF to evaluate their structural stability under simulated loading conditions.
Key performance indicators—including unconfined compressive strength, liquefaction resistance, gelling time, and viscosity—were compared against traditional silica-based grouts. The grout was also assessed for CO2 emissions, heavy metal leaching, and acute toxicity in rats and fish to determine its environmental impact.
Results and Discussion
CSRGF grout exhibited low initial viscosity, making it easy to inject into the soil. As gelation progressed, viscosity increased significantly, ensuring the grout remained in place and set properly. This transition from a highly permeable to a stable gel state was crucial for effective soil stabilization.
The gelling time of CSRGF grout was strongly influenced by pH. In acidic conditions (pH 2–4), the grout gelled rapidly, allowing for adjustable setting times based on construction needs. SAXS analysis confirmed the formation of a cohesive silica network, which contributed to the grout’s mechanical strength and durability.
Unconfined compressive strength increased with silica concentration and continued to improve over time due to chemical interactions during the curing process. The freshly prepared CSRGF grout had a pH range from acidic to neutral, reducing silica solubility and minimizing long-term leaching.
The grout also demonstrated enhanced liquefaction resistance, with higher concentrations yielding stronger soil stabilization. Compared to conventional silica-based grouts, CSRGF exhibited superior compressive strength and liquefaction resistance. Its longer gelling time and lower initial viscosity improved workability and penetration into fine soil structures, making it particularly suitable for real-world applications.
Conclusion
This study provides a comprehensive evaluation of CSRGF grout, a sustainable alternative to traditional silica-based grouts for soil stabilization. The findings highlight its superior performance in enhancing compressive strength and liquefaction resistance while significantly reducing CO2 emissions and environmental toxicity.
CSRGF grout is particularly promising for geotechnical projects in earthquake-prone regions that require high liquefaction resistance and adherence to environmental regulations. However, further field trials are necessary to validate its real-world effectiveness and long-term performance.
Journal Reference
Terui, T., Motohashi, T., Sasahara, S., & Inazumi, S. (2025). Development and application of geothermally derived silica grout for carbon-neutral soil stabilization. Case Studies in Construction Materials, 22, e04297. DOI: 10.1016/j.cscm.2025.e04297, https://www.sciencedirect.com/science/article/pii/S221450952500096
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