CO2 can be turned into sustainable concrete

A NEW method for making concrete cement from limestone and CO₂ has been developed by researchers at the US’ University of California, Los Angeles (UCLA).

Cement production in the larger concrete production process accounts for 5% of CO₂ emissions produced globally. The team aims to integrate the discovery into a long-term closed-loop system in which the cement substitute can be made from captured carbon from power plants.

During the current cement manufacturing process, CO₂ is produced during calcination, where the limestone is heated to approximately 750°C. The process separates limestone into calcium oxide – lime – and CO₂. When lime is combined with water, it forms a more stable compound called calcium hydroxide. CO₂ is also produced when lime and sand are combined with water at 1,500°C to produce concrete.

The team’s method uses CO₂ given off during calcination which can be captured and recombined with calcium hydroxide to recreate limestone. The team have since used their proof of concept to construct 5 cm cones of the cement substitute, CO₂NCRETE, shaped using 3D printing. The method is similar to how limestone cementation occurs in nature to create coral, or seashells.

Gaurav Sant, associate professor in civil and environmental engineering at UCLA, said, “While cement production results in CO₂, if we can reutilise it to make a building material which would be a new kind of cement, that’s an opportunity.

“The big challenge we foresee with this is we’re not just trying to develop a building material. We’re trying to develop a process solution, an integrated technology which goes right from CO₂ to a finished product.”

The team now hopes to scale up the process to print a 5 m beam, similar to lengths used in the construction industry. Being able to tailor the size of the beams produced will be crucial in developing the material into a commercially-viable product that is cost-effective.

JR DeShazo, professor of public policy at UCLA, said, “It takes what was a problem and turns it into a benefit in products and services that are going to be very much needed.”

Ind. Eng. Chem. Res, DOI: 10.1021/acs.iecr.5b02356