Washington State University has created a practical formula for carbon-negative, environmentally friendly concrete that is almost as strong as conventional concrete.
Graduate student Zhipeng Li and Professor Xianming Shi. Image Credit: Washington State University
In a proof-of-concept experiment, the researchers mixed normal cement with environmentally friendly biochar, a type of charcoal made from organic waste that was previously reinforced with concrete effluent. The biochar was able to absorb up to 23% of its weight in carbon dioxide from the air while maintaining a strength equivalent to conventional cement.
The study has the potential to drastically reduce carbon emissions from the concrete sector, which is one of the most energy- and carbon-intensive of all manufacturing industries. The research, headed by Doctoral student Zhipeng Li, has been published in the journal Materials Letters.
We’re very excited that this will contribute to the mission of zero-carbon built environment.
Xianming Shi, Study Corresponding Author and Professor, Department of Civil and Environmental Engineering, Washington State University
Every year, over 4 billion tons of concrete are produced worldwide. Ordinary cement production necessitates high temperatures and the combustion of fuels. The limestone used in its production also goes through decomposition, which produces carbon dioxide, so cement production is thought to be responsible for about 8% of total global carbon emissions by human activities.
Researchers attempted to use biochar as a substitute in cement to make it more environmentally friendly and lower its carbon footprint, however, adding even 3% biochar affected the strength of the concrete significantly.
The WSU investigators were able to add up to 30% biochar to their cement mixture after processing biochar in the concrete washout effluent. After 28 days, the biochar-amended cement paste had a compressive strength comparable to regular cement of roughly 4,000 pounds per square inch.
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.
Xianming Shi, Study Corresponding Author and Professor, Department of Civil and Environmental Engineering, Washington State University
The caustic concrete washout water is a sometimes classed as a problematic waste material from concrete production. According to Shi, the effluent is quite alkaline but also a good source of calcium. The calcium was employed to encourage the development of calcite, which improves the biochar and, eventually, the concrete that incorporates the biochar.
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 of biochar because we’ve figured out how to engineer the surface of the biochar.
Xianming Shi, Study Corresponding Author and Professor, Department of Civil and Environmental Engineering, Washington State University
DUe to the synergy between the extremely alkaline wastewater with a high calcium content and the highly porous biochar, calcium carbonate precipitated onto or into the biochar, strengthening it and enabling the capture of carbon dioxide from the air. The substance is projected to continue sequestering carbon dioxide for the lifetime of the concrete, which is generally 30 years in pavement and 75 years in bridges.
The researchers have been working with the Office of Commercialization to safeguard their intellectual property and have filed a provisional patent application on their carbon-negative concrete work in order to commercialize this technology.
The Washington Research Foundation has awarded them a seed grant to produce more data for a number of use cases. They are also seeking building and construction industry partners to scale up manufacturing for field demonstrations and licensing of this WSU technology.
Journal Reference:
Li, Z., & Shi, X. (2023). Towards sustainable industrial application of carbon-negative concrete: Synergistic carbon-capture by concrete washout water and biochar. Materials Letters. doi.org/10.1016/j.matlet.2023.134368.