Adding bacteria can make concrete greener

of the world’s most important materials. But making the cement that binds it generates about 8% of anthropogenic carbon-dioxide emissions. This is not just because of the heat involved. That could, in principle, be supplied in environmentally friendly ways. It is, rather, embedded in the very chemistry of the process. The heat is applied to limestone, to break up its principal constituent, calcium carbonate, into calcium oxide (cement’s crucial ingredient) and CO.