Clinker appears as lumps or nodules in the manufacture of Portland cement, typically 3 millimeters (0.12 in) to 25 millimeters (0.98 in) in diameter, created by sintering fusing together without melting to the point of liquefaction calcareous and aluminosilicate materials such as clay during the cement kiln process. It is generated in the rotary kiln by heating calcareous and clay to the liquefaction level at around 1400 ° C-1500 ° C. Clinker creates cement if combined to gypsum to monitor the cement settling properties and to maintain compressive strength or finely ground.
Composition and Preparation
- Clinker is made up of different silicates of calcium, namely alite, and belite. Certain specific components include tricalcium aluminum and calcium aluminoferrite. Such components are often generated in situ by heating different clays and calcareous.
- Portland cement clinker is rendered by heating at high temperatures a homogeneous combination of raw materials in a revolving kiln. The chemical reaction components average about 1,450 ° C (2,640 ° F) at their sintering point. Aluminum oxide and iron oxide are present only as a flux to reduce the sintering temperature and contribute little to the cement strength. It is necessary to limit the amount of tricalcium aluminate produced for specific blocks of cement, such as low heat (LH) and sulfate resistant (SR) forms.
- The primary raw material for clinker development is typically calcareous combined with a second supply comprising clay as an alumino-silicate origin. An impure calcareous comprising clay and silicon dioxide (SiO2) is usually used.
- The amount of this calcium carbonate (CaCO3) can be as small as 80 percent. Second raw materials other than calcareous in the raw mix rely on calcareous purity. Some of the second utilized raw materials are: cement, gravel, stone, iron ore, bauxite, fly ash and slag.
- Through scanning electron microscopy and atomic force microscopy, the clinker layer and its reactions in various electrolytic solutions are studied.
The chemical analysis of clinker is usually given in oxide form, as follows (in oxide weight %):
At room temperature, the raw materials inserted into the kiln were extracted. The temperature continues to rise inside the kiln, and clinker is created by rapid cooling when it reaches its peak. Although the reaction stages often overlap, in a sharply defined sequence they can be interpreted as follows:
- 65-125°C: Free water evaporates: it is important to provide latent heat. Total heat input: clinker of 2145 kJ / kg.
- 400-650°C: Clays break down endothermically and alkalis lead with liquid sulfates with the kiln environment. Net heat input: clinker of 42.2 kJ / kg.
- 500-650°C: Dolomite is endothermically decomposed. Total production of energy: 19.7 kJ.
- 650-900°C: Endothermically, calcium carbonate interacts with silica to create the “beginning belite.” The total output of heat: 722.5 kJ
- 700-900°C: To shape incipient aluminum and ferrite, calcium carbonate interacts endothermically with aluminum or iron oxide. The net output of heat: 207.2 kJ.
- 900-1050°C: The residual calcium carbonate decomposes endothermically to calcium oxide when all available silica, alumina, and iron oxide have responded.
- 1300-1425°C: Endothermically heat the iron, ferrite, and most of the belite, and belite combines to form alite with calcium oxide.
- 1425-1300°C: The melt re-freezes exothermically in aluminate, ferrite, and belite upon reaching high pressure.
Types of Clinker
This includes 76% alite, 5% belite, 2% aluminum tricalcium, 16% aluminoferrite tetra calcium, and 1% calcium oxide safe. The output has declined in recent years because the use of granulated blast furnace slag for cement manufacturing makes it easy to acquire sulfate resistance.
- Sulfate Resistant Clinker.
- Low Heat Clinker.
- White Clinker.
- Low-alkali Clinker.
- Belite Calciumsulfoaluminate Ternesite (BCT).
Sulfate Resistant Clinker
This includes 76% alite, 5% belite, 2% aluminum tricalcium, 16% aluminoferrite tetra calcium, and 1% free oxide of calcium. The output has declined in recent years because the use of granulated blast furnace slag for cement manufacturing makes it easy to acquire sulfate resistance.
Low Heat Clinker
This includes 29% alite, 54% belite, 2% aluminum tricalcium, and 15% aluminoferrite tetra calcium, with very little free lime. It is no longer produced due to the excellent low heat properties of cement produced from ordinary clinker and ground granulated blast furnace slag.
White Clinker
This comprises 76% alite, 15% belite, 7% aluminum tricalcium, no aluminoferrite tetra calcium, and 2% free lime, but the composition can vary widely. Black clinker contains black concrete that is used in building for aesthetic purposes. Many white types of cement are used in pre-cast concrete applications produced by the manufacturer. Read More
Low-alkali Clinker
Reduction of alkali content in clinker is achieved either by swapping the raw-mix alumina supply with another element thus sourcing a more costly product from a distant origin or by adding an “alkali bleed” which involves removing some of the high-temperature gases in the kiln process which includes the alkalis as a fume, contributing to some energy wastage.
Belite Calciumsulfoaluminate Ternesite (BCT)
This method is used to generate a sort of clinker with up to 30 percent lower emissions of carbon dioxide. Energy efficiency is increasing and the manufacturing process’s electricity costs are also around 15 percent lower.
Use of Clinker
Portland cement clinker is ground to a fine powder and is used as a binder in many cement goods. Sometimes a small amount of gypsum is added. It can also be mixed with other active ingredients or chemical admixtures to create certain cement forms including:
- ground granulated blast furnace slag cement
- pozzolana cement
- silica fume cement
Clinker can be held for several months without significant quality loss when preserved in dry conditions. Because of this, and because normal mineral processing machines can easily handle it, clinker is sold in large quantities worldwide. Cement producers who purchase clinker typically grind it at their cement plants as an alternative to their own clinker. For places where cement-making raw materials are not usable, producers still ship clinker to grinding plants.