Concrete is the second-most abundant material on Earth, after water. Traditionally, it's made using cement, a carbon-intensive process that accounts for 5 per cent of the world's CO2 emissions.
Carbicrete from Montreal has devised a way to make concrete without using cement, replacing it in the mix with steel slag, which is industrial waste. Not only are emissions reduced by avoiding the need for cement: the concrete is cured with CO2, permanently sequestering it within the construction project. As a result, concrete products made using this technology are carbon-negative.