For everyone passionate about sustainability, especially geotechnical and backfill engineers. This one’s for you.
The Problem
Cement is everywhere, from underground mine backfill to surface stabilization. But there’s a catch: producing 1 kg of cement releases roughly 1 kg of CO₂ into the atmosphere (Andrew, 2018). That makes it a major driver of global greenhouse gas emissions and a critical target in the race toward decarbonization.
The Objective
Develop a non-cement alternative for soil and ground strengthening that delivers mechanical stability without a heavy carbon footprint.
The Experiment
Researchers are now exploring a bio-binder produced through a reaction of urea, a calcium salt, and enzymes, a process known as Enzyme-Induced Carbonate Precipitation (EICP).
The chemistry is simple but powerful:
- The enzyme urease hydrolyzes urea to produce carbonate ions.
- These ions react with calcium (Ca²⁺), forming calcium carbonate (CaCO₃), which binds soil particles together.
Ingredient sources:
Urea – fertilizer from rural farms
Calcium – natural rock salt (NaCl)
Enzymes – extracted from jack bean or soybean meal
Early Findings
- Strength improvement: Laboratory tests show significant increases in unconfined compressive strength (UCS), even with low carbonate content (Almajed et al., 2019).
- Lower emissions: The process releases far less CO₂ than cement hydration, aligning with sustainability goals (Cheng & Cord-Ruwisch, 2012).
- Better permeability control: EICP treatment reduces soil permeability and enhances durability, especially in sandy and silty soils (Jiang & Soga, 2017).
Key Challenges
- Ammonium by-product: Urea hydrolysis produces ammonium, which can pose environmental and groundwater concerns if not managed properly (Whiffin et al., 2007).
- Non-uniform precipitation: Achieving even distribution of calcium carbonate at scale remains a challenge; clogging often occurs near injection points (Montoya et al., 2013).
- Enzyme sensitivity: The urease enzyme degrades under unfavourable pH or temperature conditions, affecting consistency (Li et al., 2021).
- Economic feasibility: Enzyme production and stabilization costs are still higher than those of conventional cement (Al Qabany & Soga, 2013).
Field Considerations
- Temperature and pH variability in real soils can slow carbonate formation.
- Heterogeneous flow paths may cause uneven cementation or localized weakening.
- Groundwater movement can dilute reactants or spread ammonium by-products.
- Injection systems must be carefully designed to prevent premature clogging and ensure uniform depth treatment.
- Durability testing under freeze–thaw, cyclic loading, and long-term chemical exposure remains limited and is needed to establish confidence in mine and infrastructure applications.
Why It Matters
If proven scalable, EICP bio-binders could transform the way we stabilize ground delivery:
- Safer mines for underground workers
- Environmentally responsible tailings backfill systems
- Cleaner water and soils in rural and mining-affected communities
This is more than an experiment. It is a step toward holistic, low-carbon engineering, where innovation, safety, and sustainability intersect to create lasting value for both people and the planet.
References
- Al Qabany, A., & Soga, K. (2013). Effect of chemical treatment used in MICP on engineering properties of cemented soils. Géotechnique, 63(4), 331–339.
- Almajed, A., Tirkolaei, H. K., Kavazanjian, E., & Hamdan, N. (2019). Enzyme-induced carbonate precipitation (EICP) columns for soil improvement. Scientific Reports, 9(1), 1132.
- Andrew, R. M. (2018). Global CO₂ emissions from cement production. Earth System Science Data, 10(1), 195–217.
- Cheng, L., & Cord-Ruwisch, R. (2012). In situ soil cementation with ureolytic bacteria: Process kinetics and modeling. Geotechnique, 62(4), 379–380.
- Jiang, N., & Soga, K. (2017). Laboratory investigation of EICP-treated sand. Journal of Geotechnical and Geoenvironmental Engineering, 143(5), 04017012.
- Li, M., Zhu, L., & Zhang, C. (2021). Environmental performance of enzyme-induced carbonate precipitation for soil stabilization. Applied Sciences, 11(12), 5391.
- Montoya, B. M., DeJong, J. T., & Boulanger, R. W. (2013). Strength, stiffness, and stress-dilatancy response of bio-cemented sand. Journal of Geotechnical and Geoenvironmental Engineering, 139(4), 579–590.
- Whiffin, V. S., van Paassen, L. A., & Harkes, M. P. (2007). Microbial carbonate precipitation as a soil improvement technique. Geomicrobiology Journal, 24(5), 417–423.
