Cement manufacture

Published on 30 January 2008 (updated on 13 February 2008)

In order to ensure that the cement produced is of constant quality, great care is taken when sampling, proportioning and mixing the raw materials so the composition remains absolutely stable over time.

Quarrying and production of the raw materials
The raw materials (limestone and clay) are taken from quarries, generally by blasting with explosive. The rock is transported by loaders and dumpers
to a crusher house.
In order to ensure that the cement produced is of constant quality, great care is taken when sampling, proportioning and mixing the raw materials so the composition remains absolutely stable over time.

A quarry

Drying and grinding
To improve the reactivity of the cement, the raw materials are dried and ground into a very fine powder in ball mills.
This also homogenizes the mixture of raw materials. The powder is stored in a silo before being placed in the kiln.

Cooking
The first chemical reactions are started by placing the powder in a heat exchanger. It is then fed into a rotary kiln and heated to
1450°C. On leaving the kiln, the glowing nodules are air-hardened on a cooling grid and where their temperature falls to about 100°C.
A sequence of physico-chemical reactions occurs during the cooking process, resulting in the production of clinker.
A variety of fuels can be used to fire the kiln - coal, petroleum coke, gas, but also alternative fuels (waste products from other industries).

Cooking of the powder in a kiln

From clinker to cement

To obtain cement with active hydraulic properties, the clinker must be very finely ground in ball mills. It is during the grinding process that the gypsum, which is essential for regulating the setting process, is added. The result is "Portland" cement. "Additive cements" are obtained by adding minerals to the clinker and gypsum (limestone, slag, fly ash, etc.).

Control room
Technicians in a control room monitor all phases of production, 24 hours a day and 7 days a week..

Quality control
The strength and durability of structures depend on the quality of the cement. Cement must meet very stringent French and European standards to which manufacturers are committed.

Shipment
Cement is stored in silos before leaving the factory by lorry, train or boat. It is delivered either in bulk or in 25 or 35 Kg bags.