Imma Perfetto
Cosmos science journalist
As countries around the globe work towards transitioning all facets of their economies to net zero emissions, engineers from the University of Southern California in the US have devised a new method to take carbon dioxide captured from the atmosphere and convert it into durable and fire-resistant building materials.
The manufacturing of building materials and products, such as steel, cement, and glass, was responsible for around 11% of global carbon emissions in 2018. There is an urgent need to find new ways to produce building materials that are carbon-neutral or, better yet, which store more carbon than gets released when they’re made.
The new manufacturing method is inspired by corals which convert carbon dioxide into hard, stony skeletons. It is described in a new study published in npj Advanced Manufacturing.
“This is a pivotal step in the evolution of converting carbon dioxide,” says Qiming Wang, associate professor of civil and environmental engineering at USC and corresponding author of the paper.
“Unlike traditional carbon capture technologies that focus on storing carbon dioxide or converting it into liquid substances, we found this new electrochemical manufacturing process converts the chemical compound into calcium carbonate minerals in 3D-printed polymer scaffolds.”
Stony corals build their hard skeletons through a process known as biomineralisation.
“As an organism, coral can use photosynthesis to capture carbon dioxide from the atmosphere and convert it into a structure,” says Wang.
The process involves combining the CO2 with calcium ions from seawater to make aragonite – a crystalline from of calcium carbonate – which forms around an inner organic template called a septum.
Wang’s team replicated this process by 3D-printing polymer scaffolds in septa-inspired lattice structures. They then coated this with a thin conductive layer of palladium, though they say that cobalt sulphide, titanium, and nickel may be alternative options.
These structures were then hooked up to electrochemical circuits as cathodes and immersed in a calcium chloride solution. When CO2 was added, it hydrolysed to form bicarbonate ions which reacted with the calcium to produce calcium carbonate.
This calcium carbonate gradually filled in the lattice structure over 4 days, resulting in a dense, mineral-polymer composite material with “extraordinary mechanical strength and fracture toughness”.
The researcher calculate that a 4-day reaction incorporates 2,720kg of CO2 per tonne of 3D-printed structure, which is much higher than carbon-negative concrete (150kg/t).
Cracks can be repaired by connecting the structures to low-voltage electricity and, unexpectedly, the material also has fire-suppressing qualities.
“The manufacturing method revealed a natural fire-suppression mechanism of 30 minutes of direct flame exposure,” Wang says.
“When exposed to high temperatures, the calcium carbonate minerals release small amounts of carbon dioxide that appear to have a fire-quenching effect. This built-in safety feature provides significant advantages for construction and engineering applications where fire resistance is critical.”
Their lifecycle assessment indicates that the structures have a negative carbon footprint, with the amount of CO2 captured exceeding the emissions associated with its manufacture and use.
The researchers see a future where buildings could be constructed from prefabricated, modular carbon-negative units, which “are expected to continuously sequester CO2 from the atmosphere to strengthen the buildings’ mechanical strength and resistance.”
