Scientists say they have invented a “carbon-negative” alternative to sand that could be used to build homes more sustainably.
Made from seawater, the material invented by US scientists is described as a greener way of making cement and concrete, which typically contain sand. Researchers say the new material is as strong and can “permanently” lock away atmospheric CO2.
Building houses contributes to climate change because making cement requires temperatures of more than 1,000°C that cannot easily be reached without burning fossil fuels. One idea being developed is for the CO2 produced to be stored underground or under the sea, instead of being released into the atmosphere.
Now the Northwestern University scientists say they are tackling both problems by “locking away CO2 permanently and turning it into valuable materials”. They say their new material can hold more than half its weight in carbon dioxide.
“We have developed a new approach that allows us to use seawater to create carbon-negative construction materials,” said Alessandro Rotta Loria, an engineer who led the research. He said cement, concrete, paint and plasters are all derived from sand.
“Currently, sand is sourced through mining from mountains, riverbeds, coasts and the ocean floor,” he said. “We have devised an alternative approach to source sand – not by digging into the Earth but by harnessing electricity and CO2 to grow sand-like materials in seawater.”
Inspired by sea shells
Prof Rotta Loria said that the way the material is made is similar to how coral and molluscs use energy to form their shells from calcium.
Instead of using the energy of the sea creatures, the scientists insert an electric current into the seawater to change its chemical composition.
There is then a chemical reaction that produces “solid minerals” which can be grown into sand. “We showed that when we generate these materials, we can fully control their properties, such as the chemical composition, size, shape and porosity,” Prof Rotta Loria said. “That gives us some flexibility to develop materials suited to different applications.”
These materials can be used in concrete as a substitute for sand and gravel, or to manufacture cement, according to the scientists. Their ability to store CO2 makes them potentially “carbon negative”.
It was not clear how much the new material might cost. Estimates presented at last year's Cop29 climate summit warned of a potential 40 per cent markup on the cost of making concrete sustainably, although experts said not all of that would necessarily be passed on to consumers.
The scientists' findings are published in the journal Advanced Sustainable Systems. Researchers at Cemex, a building materials company, contributed to the study.
