Cement manufacturing generates large amounts of CO2 during a physical-chemical process called "decarbonation". In this process, limestone is heated to very high temperatures to produce clinker, which then is ground down to produce cement.
However, the amount of clinker required can be reduced by substituting alternatives called cement admixtures.
Reducing the amount of clinker in cement offers two advantages:
reduced consumption of natural, nonrenewable raw materials,
reduced greenhouse gas emissions: cement produced with 30% admixtures produces 27% less CO2 than conventional cement.
Cement admixtures may be:
of natural origin, using limestone or pozzolanic rock,
of industrial origin, using waste products from other industries with the same hydraulic binding properties as clinker. These include slag from blast furnaces and fly ash from coal-fired power plants.
Lafarge takes a proactive approach to the use of alternative raw materials, consuming 21 million tons of industrial admixtures each year, with volume growing by 9% annually.