Cement is a fine powder which sets after a few hours when mixed with water, and then hardens in a few days into a solid, strong material. Cement is mainly used to bind fine sand and coarse aggregates together in concrete.
 

Cement is a hydraulic binder, i.e. it hardens when water is added.

There are 27types of common cement which can be grouped into 5 general categories and 3 strength classes: ordinary, high and very high.

In addition, some special cement exist like sulphate resisting cement, low heat cement and calcium aluminates cement.

The raw materials for cement production are quarried using powerful excavators or explosive materials.

The raw materials are crushed by special machinery into pieces usually smaller than 30 millimetres in size.
 

First, clinker is produced from raw materials.

In the second step cement is produced from cement clinker.

The first step can be a dry, wet, semi-dry or semi-wet process according to the state of the raw material.
 

The raw materials transported to the Plant undergo crushing with the help of huge crushers and then are either stored separately, or they are directly driven to prehomogenization piles. Next, via a fully automated system, comprising weighing devices of high accuracy and conveyor belts, the crushed raw materials are driven into the mill (roller mill or ball bearing mill) for further fine grinding.
 

The output, labelled as «raw meal», is stored into special silos for the homogenizing process, which is carried out with the help of blowers installed at the silos' bottoms. Next, the raw meal is taken to the storage silos wherefrom it is driven to the silos for the feeding of the Rotary Kiln, where the intermediate output, called «clinker», is produced.
 

For the production of one ton of clinker around 1.6 tons of raw materials are utilized (70-85% limestone, 10-20% shale etc.) and over 0.1 ton of coal.
 

The raw materials are delivered in bulk, crushed and homogenised into a mixture which is fed into a rotary kiln. This is an enormous rotating pipe of 60 to 120 m long and up to 6 m in diameter. This huge kiln is heated by a 2000°C flame inside of it. The kiln is slightly inclined to allow for the materials to slowly reach the other end, where it is quickly cooled to 100-200°C.
 

With the usage of cyclone system and a limestone grinder, the raw meal, prior to it’s feeding into the Rotary Kiln, undergoes thermal processing at 900 degrees C. The Rotary Kiln temperature is gradually raised up to 1450 degrees C and its final output, which is in granular form, is the result of the chemical decomposition of CaCO3 and of the alumina-silicate compounds and the result of chemical reactions between CaO and the oxides of Si, Al and Fe which are thus produced.
 

Four basic oxides in the correct proportions make cement clinker: calcium oxide (65%), silicon oxide (20%), alumina oxide (10%) and iron oxide (5%). New compounds are formed: silicates, aluminates and ferrites of calcium. Hydraulic hardening of cement is due to the hydration of these compounds.

The final product of this phase is called “clinker”. These solid grains are then stored in huge silos.

The second phase is handled in a cement grinding mill (made of metallic cylinders, containing several tons of grinding media, that are necessary when the grinding process takes place), which may be located in a different place to the clinker plant.

Gypsum (calcium sulphates) and possibly additional cementitious (such as blast furnace slag, coal fly ash, natural pozzolanas, etc.) or inert materials (limestone) are added to the clinker. All constituents are ground leading to a fine and homogenous powder.
 

Clinker is the basic ingredient of cement, and it largely determines the quality of the end product. Cement, as a finished product is a very fine powder that requires for its manufacture a mix of clinker, gypsum and certain natural or artificial materials (such as pozzolana), which grant beneficial properties to the cement. The cement mills resemble the raw meal mills. The exact mix of materials is strictly specified and continuously monitored. The type of cement and level of compressive strength - which is the most important characteristic - depend on the chemical composition of the clinker, the duration of the grinding and the presence or absence of various additives.

The cement is then stored in silos before being dispatched either in bulk or bagged using special silo trucks or ships.

As an example, during the pre-calcining process, the meal should be previously submitted to thermal elaboration in an environment of 900oC temperature. This is reached through the conveyance of the material into a vertical cyclone system. The meal crosses, due to gravity, the cyclone system, to reach the entrance of the rotary kiln. Simultaneously, through the cyclones and having the opposite direction, ascend the hot gases from the kiln, producing the thermal elaboration. For the achievement of the best, desirable outcome of the thermal procedure, the described cyclone system should include at least five (5) stages (five cyclones in vertical order). Taking into consideration the required material quantities and the above mentioned best available practice, the total estimated height of the cyclone system is between 70 and 100m. As a result, a steel or

reinforced concrete tower of appropriate height is needed.

This tower should be equipped with additional machinery (due to low cost requirements) as well as big fans for hot gas flow from the rotary kiln burner, as described above. These special fans beside their heavy loads, enforce vibrations to the structure.

This makes the design of such structures absolutely specialized, in order to achieve the above mentioned best available practices. The same practice is applied to the design and study of all the installations that constitute a cement production plant.