A team of researchers at Washington State University has developed a technology that could enable biochar to increasingly absorb carbon dioxide. The results, published on Science Direct, shed light on a transition to greener cement production.
Researchers have achieved significant progress in developing an environmentally friendly cement through a proof-of-concept study. They accomplished this by incorporating biochar, strengthened with concrete wastewater, into regular cement. The experimental study results in a CO2 absorption of up to 23% without reducing cement’s initial strength
Led by doctoral student Zhipeng Li, the study demonstrates the potential of this advancement in the shift toward the future of zero-carbon emission. Professor Xianming Shi, from the Department of Civil and Environmental Engineering at WSU, expressed excitement about the findings and the prospects of this carbon-negative concrete.
Previous attempts to integrate biochar into cement faced challenges, as even a three percent addition would compromise the concrete’s strength. However, the researchers successfully addressed this issue by treating the biochar with concrete washout wastewater. This treatment enabled the inclusion of up to thirty percent biochar in the cement mixture.
The resulting biochar-amended cement exhibited a compressive strength similar to ordinary cement, reaching approximately 4,000 pounds per square inch after 28 days. Professor Shi emphasized their commitment to discovering innovative ways to repurpose waste streams in concrete production, transforming them into valuable resources through chemical engineering.
The use of highly alkaline concrete washout wastewater, which contains calcium, played a crucial role in this research. The presence of calcium facilitated the formation of calcite, benefiting the biochar and ultimately enhancing the performance of the concrete incorporating biochar.
Previous studies typically limited the addition of biochar to three percent as a substitute for cement. However, by engineering the surface of the biochar, the researchers were able to add significantly higher dosages. This breakthrough enables a higher concentration of biochar in the cement mixture.
The combination of the highly alkaline wastewater, rich in calcium, and the porous nature of biochar led to the precipitation of calcium carbonate onto or into the biochar. This process strengthened the biochar and facilitated the capture of carbon dioxide from the air. Concrete made with this material is expected to continue sequestering carbon dioxide throughout its lifespan, which could range from 30 years for pavement to 75 years for a bridge. The team has filed a provisional patent application for their carbon-negative concrete and is actively seeking industry partners to scale up production for field demonstrations and licensing purposes.
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