how cement and concrete are made

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 CO2 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.

Cement is only a small part of the recipe for concrete, typically making up only about 7% to 10% of the concrete mix. The other basic components of concrete are sand, gravel (fine and coarse aggregate) and water.

Chemicals — called admixtures — are sometimes added during the concrete production stage to trap air, remove water, change the viscosity, and alter other performance properties. Producers enhance the bonding process of cement at the concrete production stage with supplementary cementing materials (SCMs), which come from industrial waste streams.

The core ingredients of cement (limestone, sand, and clay) and concrete (cement mixed with sand, gravel, and water) are among the most commonly available raw materials on Earth. 

Concrete's basic ingredients   Recylable Crushed Concrete   Retaining gabion wall made with recycled concrete
Cement powder   Concrete's basic ingredients: (cement mixed with sand, gravel, and water)   Proportion of the various ingredients in a typical concrete mix