Different minerals need to be mined in order to make cement. Limestone (containing the mineral calcite), clay, and gypsum make up most of it. The cement raw materials, especially limestone, are geologically widespread.
There are more than twenty types of cement used to make various specialty concrete, however the most common is Portland cement.
Cement manufacturing is a complex process that begins with mining and then grinding raw materials that include limestone and clay, to a fine powder, called raw meal, which is then heated to a sintering temperature as high as 1450 °C in a cement kiln. In this process, the chemical bonds of the raw materials are broken down and then they are recombined into new compounds. The result is called clinker, which are rounded nodules between 1mm and 25mm across. The clinker is ground to a fine powder in a cement mill and mixed with gypsum to create cement. The powdered cement is then mixed with water and aggregates to form concrete that is used in construction.
Clinker quality depends on raw material composition, which has to be closely monitored to ensure the quality of the cement. Excess free lime, for example, results in undesirable effects such as volume expansion, increased setting time or reduced strength. Several laboratory and online systems can be employed to ensure process control in each step of the cement manufacturing process, including clinker formation.
Accurate cement production also depends on belt scale systems to monitor output and inventory or regulate product loadout, as well as tramp metal detectors to protect equipment and keep the operation running smoothly. The Cement Manufacturing Process flow chart sums up where in the process each type of technology is making a difference.