Buildings feel hotter than their surrounding environs in the summer in part because of the materials that they are built with. Concrete absorb sunlight and store the energy as heat, raising the temperatures of indoor spaces. This then makes people crank up energy-hungry air conditioners.
But researchers in China’s Southeast University have now turned that problem on its head with a new cooling cement that could help bring building temperatures down without using electricity. The cement looks and behaves just like regular cement, but it can reduce indoor temperatures by a few degrees.
Making cement and concrete results in about 8 percent of the world’s carbon dioxide emissions. The emissions don’t end there. Buildings consume about 40% of global energy and emit around 36% of global carbon emissions, the researchers write in Science Advances, much of which come from building operations. “The need for space cooling has been growing rapidly due to global warming, population growth, and rising living standards,” they write.
A method called radiative cooling has recently emerged as a promising way to cool people and spaces without consuming electricity. The method relies on materials that reflect sunlight and emit heat, or infrared radiation, through the atmosphere into space.
The Southeast University team tweaked the chemistry and structure of cement to make it a radiative cooling material. “We have innovatively transformed cement materials from heat absorbers to heat reflectors using a bottom-up approach,” they write in the paper.
The researchers started with raw materials that were rich in calcium, alumina, silica, and sulfur. The combination of alumina and sulfur compounds helps the material emit radiation in the mid-infrared range.
The modified cement mix also forms extra ettringite, which is a calcium aluminum sulfate mineral normally found in cement in small amounts. The researchers use a rubber mold to apply pressure and create cement containing lots of ettringite crystals of different sizes. This mix of crystals scatters light in different directions.
The cool cement displayed high strength in laboratory tests. It resisted exposure to abrasion, corrosive liquids, ultraviolet radiation, and freeze-thaw cycles. Meanwhile, field tests showed that the surface temperature of the material stayed up to 5.4°C cooler than ambient air and 26°C cooler than conventional cement in full sunlight.
The process also cut the carbon footprint of the cement by 25%. The cost-effective and scalable fabrication process could allow manufacturers to use the new supercool cement in coatings, structural roofs, and walls.
“This breakthrough holds the potential to turn the heavy cement industry into a negative-carbon emission system, where supercool cement could play a key role in driving an energy-efficient, carbon-free future for the construction industry,” the researchers conclude.
Source: Guo Lu et al. Scalable metasurface-enhanced supercool cement. Science Advances, 2025.
Image by Chu Viết Đôn from Pixabay
