Traditional concrete has a carbon footprint of up to 300kg CO2 per m3. Most of this is emitted during the manufacture of cement. the binding material used in concrete. 3.5 billion tonnes of cement are produced every year. It accounts for 8% of all human-made emissions. The Finnish researchers have done away with cement altogether. They have worked out how to inject CO2 into powdered blast furnace slag. When mixed with the ash residue from burning biomass this material becomes a binder that can replace cement. It has been developed by Finnish start-up Carbonaide.