Cement of the future: Cooling cities and cutting emissions

Cement keeps our cities standing, but it also keeps them hot. Roofs and pavements absorb sunlight, store heat, and then radiate it back into the air. Air conditioners fight that heat, but they burn electricity and drive up emissions.

Fengyin Du and her team at Southeast University believe that cement itself can change the story by cooling cities instead of heating them up.

Why regular cement fails

Ordinary cement is dark and doesn’t bounce sunlight away. Instead, it absorbs the sun’s energy and traps it as heat.

The heat then moves into buildings, making rooms hotter and harder to cool. It also warms the outside environment, so streets and sidewalks feel hotter too.

When cities heat up this way, people rely more on air conditioning, which uses a lot of electricity. If we continue to use the same materials, the demand for cooling will keep growing.

By the middle of this century, the energy used for cooling could make carbon emissions up to three times higher than today.

Building a different cement

The Southeast University team took a different approach. The researchers created a cement where crystals form naturally on the surface. The mineral ettringite does the heavy lifting.

“It 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,” explained Du.

The cement also lets heat escape because of tiny pores and a gel rich in aluminum. Together, these features turn the surface into both reflector and radiator.

How the cooling cement is made

The recipe starts with common minerals like limestone, gypsum, alumina, and silica. These are shaped into pellets, heated, and then ground.

When mixed with water, the particles react to form both ettringite and gel. To shape the surface, the team used molds and air bubbles that left behind microcavities.

Crystals grow inside these cavities, creating patterns that scatter light and boost reflectivity.

Testing the cement in sunlight

The researchers placed the new cement on a rooftop at Purdue University to see how it worked in real sunlight.

The cement stayed cooler than the air around it – by 5.4°C (9.7°F) – and much cooler than normal Portland cement – by 26°C (47°F). That means it didn’t trap heat the way regular cement does.

Even at night, when there’s no sunlight, the cement kept releasing stored heat into the sky. This showed that its cooling ability doesn’t stop when the sun goes down. It can keep surfaces cooler both day and night.

Strength and resilience

Cooling power alone isn’t enough. Buildings need materials that last. The new cement showed compressive strength above 100 MPa, stronger than many traditional mixes.

It resisted scratches, stayed intact under freeze-thaw cycles, and endured immersion in corrosive liquids. After months of UV exposure and a full year outdoors, its reflectivity barely dropped.

Brighter city streets

Cement is usually gray, but the new research shows that it doesn’t have to stay that way. The team mixed in special phosphor dyes while making the cement. This produced colored versions – yellow, green, and red.

Even with the color, the cement still reflected about 90% of sunlight. That means it kept its cooling ability while also giving architects and city planners more design options to make buildings and streets look brighter.

Climate benefits of cooling cement

Production matters as much as performance. This cement is made at lower temperatures, cutting emissions during manufacture by about 25 percent.

Life-cycle studies suggest that over 70 years, a tonne of this cement could reduce up to 2,867 kilograms of CO2 compared with standard Portland cement.

Some cities, like Niamey and Mumbai, could reach carbon neutrality with it faster than others.

Cooler cities with less energy demand

Oscar Brousse from University College London praises the material’s design but warns against simple conclusions.

“It doesn’t mean that because the surface is 5°C lower, that the air temperature will be 5°C lower around it. The effect locally may be greatly limited,” said Brousse.

Even with that caution, the potential is clear. This cement could cut energy demand in cities, reduce emissions, and extend building lifespans. If scaled, it may help cool entire neighborhoods without flipping a switch.

The study is published in the journal Science Advances.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–