Researchers Develop Carbon-Negative Concrete for the Paint Industry

Researchers at Washington State University have developed a viable formula for concrete that is nearly as strong as conventional concrete, carbon-negative, and environmentally friendly. In a proof-of-concept study, researchers infused normal cement with environment-friendly biochar, a type of charcoal made from organic waste, and previously strengthened it with concrete washout water. The biochar was able to absorb carbon dioxide from the air equivalent to 23% of its weight and nonetheless achieved strength comparable to normal cement. The research could significantly reduce carbon emissions in the concrete industry, which is among the largest industries in terms of energy and carbon intensity across all manufacturing sectors. The study, conducted by doctoral student Zhipeng Li, was published in Materials Letters journal. Xianming Shi, professor in the Department of Civil and Environmental Engineering at WSU and corresponding author of the paper, stated: "We are very excited about this because it will contribute to our zero-carbon built environment mission." More than 4 billion tonnes of concrete are produced annually worldwide. Normal cement production requires high temperatures and fuel combustion. The limestone used in its production also undergoes decomposition, generating carbon dioxide, which is why cement production is thought to account for approximately 8% of total carbon emissions from human activities globally. Researchers attempted to add biochar as a substitute to cement to make it more environmentally friendly and reduce its carbon footprint, but adding biochar at a 3% rate significantly reduced the strength of the concrete. After purifying the biochar from concrete washout wastewater, WSU researchers were able to add biochar to cement mixtures at levels up to 30%. Paste made from biochar-enhanced cement was able to achieve a compressive strength comparable to normal cement of approximately 4,000 pounds per square inch after 28 days. Shi explained: "We are determined to find new ways to redirect waste streams to beneficial uses in concrete; after identifying these waste streams, the next step is to see how we can wave the magic wand of chemistry and transform them into a resource. The real trick is in interface engineering, that is, how you design the interfaces in concrete." Caustic concrete washout water is a waste material resulting from concrete production, which can sometimes be problematic. Shi stated that the washout water is highly alkaline but also serves as a valuable source of calcium. Researchers used calcium to create calcite formation that benefits the biochar and ultimately the concrete containing biochar. "Most other researchers could only add up to 3% biochar as a cement replacement, but we are demonstrating biochar use at much higher doses because we figured out how to design the surface of the biochar," he said. The synergy between highly alkaline washout water containing excess calcium and highly porous biochar meant that calcium carbonate precipitated onto or into the biochar, strengthening it and allowing it to capture carbon dioxide from the air. Concrete made from this material is expected to continue sequestering carbon dioxide throughout its service life, whether 30 years in a sidewalk or 75 years in a bridge. To commercialize this technology, researchers are working with the Commercialization Office to protect intellectual property and have filed a provisional patent application for carbon-negative concrete work. Recently, they received a seed grant from the Washington Research Foundation to generate additional data for various use cases. Additionally, they are actively seeking industry partners from the building and construction sectors for field demonstrations and to scale up production for licensing of WSU's technology. Academic Reference: Zhipeng Li et al, Towards sustainable industrial application of carbon-negative concrete: Synergistic carbon-capture by concrete washout water and biochar, Materials Letters (2023). DOI: 10.1016/j.matlet.2023.134368   Source