Cement can self-cool by reflecting light outward and dissipating heat from its surface, offering a comfortable indoor climate without reliance on air conditioning.

Traditional cement often absorbs infrared light from the sun, trapping heat and causing indoor temperatures to rise along with the surrounding air.

To tackle this challenge, Fengyin Du from Purdue University in Indiana and her team developed a unique cement that features tiny reflective mineral crystals called ettringite on its exterior.

This innovative cement releases infrared light instead of retaining it, allowing for rapid heat loss. “It acts like a mirror or radiator, reflecting sunlight and releasing heat into the atmosphere, enabling the building to remain cool without needing air conditioning or power,” Du explains.

Initially, the researchers create small pellets from commonly found minerals like limestone and gypsum. These are ground into a fine powder, mixed with water, and poured into silicon molds that contain small perforations. Air bubbles moving through these holes form slight indentations on the surface, where the reflective ettringite crystals can develop. The aluminum-rich gels in the set cement permit infrared rays to traverse the material.

Du notes the process is easily scalable and enables cement production at lower temperatures, making it $5 less expensive per tonne than conventional Portland cement.

Du and her team evaluated the temperature regulation of their cement on the hot roof of Purdue University’s campus and observed that its surface temperature was 5.4°C (9.7°F) cooler than the surrounding air and 26°C (47°F) lower compared to Portland Cement.

“It’s a valuable material,” states Oscar Brousse from University College London. “You enhance the material’s ability to reflect and emit energy, thus efficiently releasing energy that the material has absorbed.”

However, gauging just the surface temperature of a material does not convey its real-world performance. “A surface temperature reduction of 5°C translates into a 5°C decrease in air temperature, which can significantly impact local conditions.”