Cement is the essential ingredient in concrete. It is a fine powder that acts as the glue that holds concrete together when mixed with water, sand and aggregates.
Cement is manufactured by heating a precise mixture of finely ground limestone, clay and sand in a rotating kiln to temperatures reaching 1450ºC. This results in the production of cement clinker, an intermediate product in the manufacture of cement. The cement clinker emerges from the kiln, is cooled, and then finely ground to produce the powder we know as cement. The fuels combusted to heat the kiln account for about 40% of cement manufacturing emissions. The remaining 60% are “process emissions” — i.e. when limestone is superheated, it releases its carbon atoms and forms CO<sub>2</sub> in the kiln — that are effectively irreducible. The Canadian cement and concrete industry is pursuing a variety of innovative measures to further reduce its carbon footprint.