Air-conditioning demand in buildings is in large part driven by the cement used for their construction, which tends to absorb infrared radiation and store it as heat. A more sustainable cooling approach is presented by the formulation of a cement that reflects light and emits heat due to the inclusion of reflective ettringite crystals.

Nanoscale pellets composed of common minerals such as limestone and gypsum, were ground, mixed with water and poured into a silicone mold covered in small holes. Air bubbles passing through the holes create slight depressions in the cement’s surface, where the reflective ettringite crystals grow while an aluminum-rich gel in the set cement lets infrared light pass through the material.

During tests conducted on a hot roof at Purdue University in Indiana, the surface temperature of the new material was 5.4° C (9.7° F) lower than the air and 26° C (47° F) lower than that of conventional Portland cement. The cement manufacturing process devised by researchers from Southeast University (China), Jiangxi Yinshan White Cement Co. Ltd. (China), University of Chicago and Purdue University is also less costly than conventional Portland cement because it can be produced at lower temperatures.

In addition to lowering reliance on energy-intensive air-conditioning systems, the supercool cement described in Science Advances could potentially deliver a net-negative carbon footprint over a 70-year period.