Waste to foundation: Transforming construction waste into high-performance material

To tackle these interconnected challenges, scientists from Japan, led by Professor Shinya Inazumi, from the College of Engineering, Shibaura Institute of Technology (SIT), Japan, present a sustainable alternative: a high-performance geopolymer-based soil solidifier developed from Siding Cut Powder (SCP), a construction waste byproduct, and Earth Silica (ES), sourced from recycled glass. This breakthrough innovation offers an alternative to reducing cement dependence while transforming construction waste into valuable construction resources. Their paper was made available online on April 21, 2025, and was published in Volume 26 of the Cleaner Engineering and Technology journal on May 1, 2025.

The combination of SCP and ES forms a geopolymer-based solidifier capable of enhancing soil-compressive strength beyond construction-grade thresholds of 160 kN/m². Thermal treatment of SCP at 110 °C and 200 °C was a critical step, significantly improving its reactivity and reducing the material use without sacrificing material performance. "This research represents a significant breakthrough in sustainable construction materials," notes Prof. Shinya Inazumi. "By using two industrial waste products, we developed a soil solidifier that not only meets industry standards but also helps address the dual challenges of construction waste and carbon emissions."

A noteworthy aspect of the study was the approach to environmental safety. Environmental assessments initially identified concerns regarding arsenic leaching, which was partially attributed to the recycled glass content in ES. However, Prof. Inazumi explains, "Sustainability cannot come at the expense of environmental safety. Most importantly, we identified and solved a potential environmental concern: when arsenic leaching was detected in initial formulations, we demonstrated that incorporating calcium hydroxide effectively mitigated this issue through the formation of stable calcium arsenate compounds, ensuring full environmental compliance."

This solution offers numerous practical applications with wide-reaching real-world impact. Prof. Inazumi remarks, "In urban infrastructure development, our technology can stabilize weak soils beneath roads, buildings, and bridges without relying on carbon-intensive Portland cement. This is particularly valuable in areas with problematic clay soils where conventional stabilization methods are costly and environmentally burdensome."

Disaster-prone regions could benefit from rapid soil stabilization using these materials, which have demonstrated good workability and setting times compatible with emergency response needs. In addition, rural infrastructure projects in developing regions could utilize these materials to create stabilized soil blocks for construction, providing a low-carbon alternative to fired bricks or concrete.

The implications extend across industries. For the construction sector, which faces increasing pressure to decarbonize, the geopolymer solidifier offers an alternative that exceeds the performance of traditional methods without the heavy carbon footprint. For geotechnical engineering firms, its proven durability under sulfate attack, chloride ingress, and freeze-thaw cycles allow its use in demanding and aggressive environments.

Additionally, by lowering Portland cement usage, this technology supports construction projects aiming to meet green building certifications and carbon reduction targets. It may also allow developers to qualify for environmental incentives in countries where carbon pricing mechanisms are in place, further enhancing its economic viability.

Prof. Inazui emphasizes the broader vision behind his work: "By developing a geopolymer solidifier from readily available waste streams, we are not only offering a sustainable engineering solution but redefining how we value industrial byproducts in a resource-constrained world."

These findings point to a transformative shift in sustainable construction practices, potentially transforming millions of tons of construction waste into valuable resources while reducing the carbon footprint associated with cement production, which currently accounts for 7-8% of global CO₂ emissions. As global demand for infrastructure continues to rise, innovative technologies play a central role in building a more resilient and responsible future.