The carbon-negative concrete has a strength that is almost the same as regular concrete
Researchers from Washington State University have developed carbon-negative concrete in a proof-of-concept study, that is nearly as strong as regular concrete. Regular cement was infused with a known carbon sequestration agent, biochar, which is a type of charcoal made by heating biomass in the absence of oxygen. The biochar was strengthened with concrete wastewater before being infused with the cement. The biochar was able to absorb 23 per cent of its weight from the ambient air, during the process of solidification. The research can help reduce the carbon footprint of the concrete industry, which is one of the most energy intensive manufacturing industries, and is responsible for about eight per cent of global carbon emissions.
A paper describing the findings has been published in Materials Letters. The approach has the benefit of using the toxic runoff from concrete production. Corresponding athor of the paper, Xianming Shi says, “We’re very excited that this will contribute to the mission of zero-carbon built environment. We’re committed to finding novel ways to divert waste streams to beneficial uses in concrete; once we identify those waste streams, the next step is to see how we can wave the magic wand of chemistry and turn them into a resource. The trick is really in the interfacial engineering — how you engineer the interfaces in the concrete.”
While there have been previous attempts at infusing biochar with concrete, the strength of the material was not comparable to that of regular concrete. This shortcoming was addressed by infusing the biochar with the caustic concrete wastewater. While the wastewater is alkaline, but also contains calcium, which the researchers used to induce the formation of calcite. The calcite strengthens the biochar, as well as the eventual concrete. During the process, calcium carbonate precipitates onto the biochar, scrubbing carbon-dioxid from the atmosphere. The concrete made from such a material would continue to sequester carbon for the lifetime of the concrete.