China/US: A team led by Fengyin Du, then at Southeast University in Nanjing, developed a new cement formulation that reflects sunlight and emits heat more effectively than ordinary Portland cement, according to the New Scientist. The cement incorporates reflective ettringite crystals on its surface, which Du says “works like a mirror and a radiator, so it can reflect sunlight away and send heat out into the sky, so a building can stay cooler without any air conditioning or electricity.”

To make it, the researchers produce tiny pellets from limestone and gypsum, which are ground and mixed with water before being poured into a silicone mould covered in small holes. Ettringite crystals grow in slight depressions on the surface created by air bubbles, while an aluminium-rich gel allows infrared light to pass through, lowering heat retention.

Du said that tests at Purdue University, Indiana showed the cement’s surface was 5.4°C cooler than the air and 26°C cooler than conventional cement under the same conditions. The process is reportedly scalable and costs US$5/t less than ordinary Portland cement, as it can be produced at lower temperatures.