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US: Researchers at Washington State University (WSU) have developed a method for making low-carbon concrete using cement and biochar, a type of charcoal made from organic waste that is nearly as strong as standard concrete. The team, led by doctoral student Zhipeng Li, strengthened the biochar with concrete wastewater. The biochar was able to suck up to 23% of its weight in carbon dioxide from the air.

Previous attempts to add biochar as a substitute in cement have significantly reduced the strength of the resulting concrete. However, the WSU project found that by treating the biochar with concrete washout wastewater it was able to add up to 30% biochar to cement mixtures. The paste made of the biochar-amended cement was able to reach a compressive strength after 28 days comparable to that of ordinary cement. The researchers used calcium in the concrete washout water to induce the formation of calcite, which benefits the biochar and, eventually, the concrete that incorporates it.

Xianming Shi, professor in the WSU Department of Civil and Environmental Engineering, said, “We’re very excited that this will contribute to the mission of zero-carbon built environment.” He added, “Most other researchers were only able to add up to 3% biochar to replace cement, but we’re demonstrating the use of much higher dosages because we’ve figured out how to engineer the surface of the biochar.”

The synergy between the highly alkaline wastewater that contains a lot of calcium and the highly porous biochar meant that calcium carbonate precipitated onto or into the biochar, strengthening it and allowing for the capture of carbon dioxide from the air. A concrete made of the material would be expected to continue sequestering CO2 for the lifetime of the concrete, typically 30 years in pavement or 75 years in a bridge.

The researchers have been working with the WSU Office of Commercialization to protect the intellectual property and have filed a provisional patent application on their carbon-negative concrete work. They recently received a seed grant from the Washington Research Foundation to produce more data for a variety of use cases. They are also actively seeking industry partners from the building and construction sector to scale up production for field demonstrations and licensing this WSU technology.