A recent study introduces a sustainable soil solidifier made from construction and glass waste, aiming to reduce carbon emissions while maintaining the strength and durability of traditional cement-based materials.
Study: Development of environmentally sustainable geopolymer-based soil solidifiers using waste siding and glass powders. Image Credit: dee karen/Shutterstock.com
The solidifier is based on siding cut powder (SCP), an industrial by-product, activated with Earth silica (ES), an alkaline material derived from recycled waste glass. Researchers tested various SCP-ES formulations in the lab, both with and without additives such as calcium hydroxide and ordinary Portland cement (OPC), to evaluate performance across multiple curing stages.
Background
The environmental footprint of OPC has driven the search for alternative materials that offer comparable structural performance with significantly lower emissions. One promising class is geopolymers—inorganic binders formed by activating aluminosilicate-rich waste with alkaline solutions. These materials not only cut down on carbon output but also allow for the repurposing of industrial by-products.
SCP, a silica- and alumina-rich waste from the construction industry, fits well within the geopolymer framework. Paired with ES, a silica-heavy, alkaline agent made from recycled glass, the combination supports effective geopolymerization. Together, they help address two major waste streams—construction debris and glass—while forming a functional building material.
Methods
The study focused on improving a specific type of clay soil rich in montmorillonite and kaolinite, known for its swelling behavior and high cation exchange capacity. Researchers evaluated four dosages of the solidifier—50, 100, 150, and 200 kg/m3—with SCP as the base material. Some blends included OPC or calcium hydroxide at 10 % or 20 % of the solidifier volume.
To assess thermal activation, SCP was heated to either 110 °C or 200 °C for 12 hours before cooling. Each formulation included 5 % ES to enhance the alkaline activation process. Samples were cured and tested for unconfined compressive strength at 7, 28, and 91 days, alongside leaching tests for hazardous substances like arsenic, hexavalent chromium, and heavy metals. SCP was also analyzed for asbestos.
Results and Discussion
OPC-enhanced samples showed greater compressive strength than those using SCP alone, though mixes with calcium hydroxide outperformed both. Notably, SCP activated with ES alone also reached strength levels suitable for construction. Thermal treatment further improved SCP’s reactivity, reducing the quantity needed.
From an environmental standpoint, the SCP was free of asbestos, and calcium hydroxide successfully reduced arsenic leaching to meet safety standards in samples where arsenic was initially elevated.
Microstructural analysis showed the formation of silicate and aluminosilicate compounds, which are key to improving strength and stability. In samples containing OPC and ES, calcium silicate hydrate crystals also formed, reinforcing the structure.
Durability tests confirmed that SCP-ES formulations resisted chloride ingress, alkali-silica reaction, sulfate attack, and freeze-thaw cycles. For instance, samples immersed in a 5 % sodium sulfate solution for 90 days experienced less than 1 % mass loss and retained their structural integrity.
Conclusion and Future Directions
This study presents a practical and sustainable alternative to OPC-based soil solidifiers by using industrial by-products like SCP and ES. The approach not only lowers emissions but also contributes to more effective waste management in construction and glass industries.
Looking ahead, optimizing the formulations for different soil types and real-world conditions will be key. Large-scale and long-term field trials will be essential to confirm the lab findings and support wider adoption in geotechnical applications.
Journal Reference
Inazumi, S., Hashimoto, R., Hontani, Y., Yoshimoto, A., Shishido, K., & Chao, K. C. (2025). Development of environmentally sustainable geopolymer-based soil solidifiers using waste siding and glass powders. Cleaner Engineering and Technology, 26, 100976. DOI: 10.1016/j.clet.2025.100976, https://www.sciencedirect.com/science/article/pii/S2666790825000990
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