Sooner or later, even the best sidewalk in the country will develop a crack or two. When this happens, workers are deployed to either fill in the damage or lay down completely new swaths of concrete. Over 7 per cent of the world’s CO2 emissions come from cement production, so any means of prolonging the material’s life would help to reduce greenhouse gasses. Researchers at Cardiff University, the University of Cambridge, and the University of Bath are taking part in a £3m project to create self-healing concrete. The material would be able to mend itself with the help of bacteria contained within microcapsules that would germinate and produce limestone when water enters a fissure.