In the study, researchers at Washington State University infused standard cement with biochar, a type of charcoal produced from organic waste previously enriched with concrete wastewater. Biochar absorbed up to 23% of its weight in atmospheric carbon dioxide while maintaining a strength comparable to conventional cement.

Research can significantly reduce carbon emissions in the concrete industry, one of the most energy and carbon intensive sectors. The study, under the supervision of doctoral student Zhipen Li, is reported in the journalism. Material Letters.

“We are very excited that this will contribute to the mission of creating a zero-carbon environment,” said Xianming Shi, a professor in WSU’s Department of Civil and Environmental Engineering and corresponding author of the paper.

More than 4 billion tons of concrete is produced annually in the world. Conventional cement production requires high temperatures and fuel combustion. The limestone used in its production also decomposes to produce carbon dioxide, so cement production is estimated to be responsible for about 8% of total anthropogenic carbon emissions worldwide.

Researchers have tried adding biochar instead of cement to make it greener and reduce its carbon footprint, but even adding 3% biochar significantly reduced the durability of the concrete. After treating the concrete washing wastewater with biochar, WSU researchers were able to add up to 30% biochar to the cement mix. A paste made with biochar additive cement achieved a compressive strength of approximately 4,000 psi after 28 days, comparable to that of conventional cement.

“We are committed to finding new ways to redirect waste streams for beneficial use in concrete; “Once we’ve identified these waste streams, the next step will be to see how we can wave a magic wand and turn them into a resource,” said Shi. “Our main focus is to design interfaces, how to build interfaces in concrete.”

Caustic concrete washing water is sometimes a problematic concrete production waste. Shea said the sewage is highly alkaline, but it’s also a valuable source of calcium. The researchers used calcium to promote the formation of calcite, which benefits biochar and eventually biochar-containing concrete.

“Most other researchers have only been able to add up to 3% biochar to replace the cement, but we show using much higher doses of biochar because we figured out how to create a biochar surface,” he said.

The synergy between the highly alkaline, calcium-rich wastewater and the highly porous biochar caused calcium carbonate to deposit on or in the biochar, fortifying it and helping to capture carbon dioxide from the air. Concrete made with this material is expected to continue to absorb carbon dioxide throughout the life of the concrete, typically 30 years on a pavement or 75 years on a bridge.

To commercialize the technology, the researchers worked with the Office of Commercialization to protect intellectual property and applied for a preliminary patent for their carbon negative concrete work. They recently received a seed grant from the Washington Research Foundation to generate additional data for various use cases. They are also seeking industry partners from the construction industry to scale up production for field demonstrations and licensing of this WSU technology.