Roads make up over a third of the surface of many cities. Most are made of asphalt, which is becoming a liability in hot climates. Asphalt soaks up the sun and stores heat, and is known to buckle and liquefy during scorching heat waves that are becoming more common in some regions thanks to climate change.
Reflective pavements can be more than 10 °C cooler than blacktop. To keep costs low, these materials need to be easy to apply, and durable. Light-colored sealants made by companies like GuardTop that can be applied just like conventional protective coatings. Startup ePAVE, meanwhile, makes a mix of cement with a polymer-and-titanium dioxide blend that binds to asphalt and reflects infrared. The 3-mm thick overlay cures and becomes rock-hard in 20 minutes, so traffic disruption is minimal, and it should last 10 years, says CEO Klara Moradkhan. Los Angeles, Melbourne and Tokyo are piloting reflective roads, while permeable pavements made of porous asphalt or paving stones are being tested for their ability to help roads chill through evaporative cooling.