How cement may yet help slow global warming

THE ROMANSAD perfected concrete, and their legacy still stands in the form of the magnificent roof of the Pantheon, the world’s largest unreinforced concrete dome. Since it was completed in around 125 by the Emperor Hadrian, an awful lot more concrete has been poured—some 30bn tonnes every year, at the moment, to put up buildings, roads, bridges, dams and other structures. The grey stuff has become the most widely used construction material on the planet, and demand is growing.This is bad news for global warming. The problem is that concrete’s crucial ingredient, cement, which is mixed with sand, gravel and water to make the stuff, is responsible for a huge amount of greenhouse-gas emissions. Taking in its various stages of production, the 5bn tonnes of cement produced each year account for 8% of the world’s anthropogenic CO emissions. If the cement industry were a country it would be the third-largest emitter in the world, after China and America.