Clinker is a nodular material produced in the kilning stage during the production of cement and is used as the binder in many cement products. The lumps or nodules of clinker are usually of diameter 3-25 mm and dark grey in color.

It is produced by heating limestone and clay to the point of liquefaction at about 1400°C-1500°C in the rotary kiln. Clinker, when added with gypsum (to control the setting properties of cement and ensure compressive strength) and ground finely, produces cement.

Clinker can be stored for long periods of time in a dry condition without degradation of quality, hence it is traded internationally and used by cement manufacturers when raw materials are found to be scarce or unavailable.

Use of Cement Clinker: Conversion to Cement

Cement Clinker, combined with additives and ground into a fine powder, is used as a binder in cement products. Different substances are added to achieve specific properties in the produced cement. Gypsum added to and ground with clinker regulates the setting time and gives the most important property of cement, compressive strength. 

It also prevents agglomeration and coating of the powder at the surface of balls and mill wall. Some organic substances, such as Triethanolamine (used at 0.1 wt.%), are added as grinding aids to avoid powder agglomeration. Other additives sometimes used are ethylene glycol, oleic acid, and dodecyl-benzene sulphonate.

The most notable type of cement produced is Portland cement, but certain active ingredients of chemical admixtures may be added to clinker to produce other types of cement, such as:

  • ground granulated blast furnace slag cement
  • pozzolana cement
  • silica fume cement

Clinker is primarily used to produce cement. Since it can be stored in dry condition for several months without noticeable deterioration, it is traded internationally in large amounts. Cement manufacturers buy clinker for their cement plants in areas where raw materials for cement are scarce or unavailable.

How Cement Clinker is made?

The most common way to manufacture portland cement is through a dry method. The first step is to quarry the principal raw materials, mainly limestone, clay, and other materials.

After quarrying the rock is crushed. This involves several stages. The first crushing reduces the rock to a maximum size of about 6 inches. The rock then goes to secondary crushers or hammer mills for reduction to about 3 inches or smaller.

The crushed rock is combined with other ingredients such as iron ore or fly ash and ground, mixed, and fed to a cement kiln.

The cement kiln heats all the ingredients to about 2,700 degrees Fahrenheit in huge cylindrical steel rotary kilns lined with special firebrick. Kilns are frequently as much as 12 feet in diameter—large enough to accommodate an automobile and longer in many instances than the height of a 40-story building. The large kilns are mounted with the axis inclined slightly from the horizontal.

The finely ground raw material or the slurry is fed into the higher end. At the lower end is a roaring blast of flame, produced by precisely controlled burning of powdered coal, oil, alternative fuels, or gas under forced draft.

As the material moves through the kiln, certain elements are driven off in the form of gases. The remaining elements unite to form a new substance called clinker. 

PORTLAND CEMENT CLINKER

Ordinary Portland Cement Clinker is the core component in producing cement which is formed by sintering limestone. In the manufacturing of Portland cement, clinker formed by sintering or fusing together without melting to the point of liquefaction, alumina-silicate materials such as clay and limestone during the cement kiln stage and happens as 3 millimeters (0.12 in) to 25 millimeters (0.98 in) in diameter,

Ordinary Portland Cement Clinker is then ground to a fine powder and used as the binder in many Cementous goods. Sometimes, a little gypsum is also added. If stored in dry conditions, Cement Clinker can be kept for several months without considerable loss of quality. Because of this fact, and because it can be easily handled by ordinary mineral handling apparatus, Cement Clinker is highly traded intercontinentally in large quantities. At their cement plants, cement manufacturers which purchase clinker usually grind it as an addition to their own clinker. Producers also tend to ship their clinker to grinding plants in zones where cement-making raw materials are not available.

PORTLAND CEMENT CLINKER ASTM C150 TYPE I

Clinker or kiln pulp refers to dark gray grains with a diameter of 3 to 25 mm which is produced by heating clay and limestone at a temperature of 1400 to 1500°C and without changing its properties, it can be stored for a long time in a dry place. Cement factories purchase clinker to produce cement in areas where raw materials are scarce or unavailable. Cement is generally produced in two ways. In the wet method, clinker which is the raw material for cement production is mixed with water and ground, but in the dry method, the cement raw materials are mixed and ground together in a dry form.

Cement and clinker are not two similar materials. Cement is a powder-like material used in the construction industry, while clinker is a material used to produce cement. Clinker is formed in the kiln during the cement production process in such a way that the raw materials that enter the kiln are heated and when the kiln temperature rises to its highest point, clinker is produced by a sudden decrease in temperature. Types of clinker are different depending on the type of cement that is produced. Apart from Portland cement mix, the types of cement clinkers are as follows:

Sulfate-resistant clinker

White clinker

Low-alkaline clinker

Low-heat clinker

Clinker is combined with clay and additives and is used in the form of gray pellets as a material used in the cement production. Different materials are used to create special properties in the produced cement, including gypsum that is added to clinker and gives important properties to cement and increases its compressive strength. In addition, it prevents the powder accumulation and coating on the surface of the mill wall. Some organic materials such as triethanolamine are also added to the cement mix to prevent the cement clumping. However, additives such as ethyl glycol, oleic acid and dodecyl benzene sulfonate can also be added. The most important cement produced by factories is Portland cement, but certain active compounds of chemical mixtures may be added to the clinker to produce other types of cement such as Pozzolanic cement, silica foam, and so on.

PORTLAND CEMENT CLINKER ASTM C150 TYPE 2

Portland cement clinker is made by heating, in a kiln, a homogeneous mixture of raw materials to a calcining temperature, which is about 1450°C for modern cements. The aluminium oxide and iron oxide are present as a flux and contribute little to the strength. For special cements, such as Low Heat (LH) and Sulfate Resistant (SR) types, it is necessary to limit the amount of tricalcium aluminate (3 CaO•Al2O3) formed. The major raw material for the clinker-making is usually limestone (CaCO3) mixed with a second material containing clay as source of alumino-silicate.

Normally, an impure limestone which contains clay or SiO2 is used. The CaCO3 content of these limestones can be as low as 80%. Secondary raw materials (materials in the rawmix other than limestone) depend on the purity of the limestone. Some of the materials used are clay, shale, sand, iron ore, bauxite, fly ash, and slag. When a cement kiln is fired by coal, the ash of the coal acts as a secondary raw material.