Cement

Cement, one of the material used in forming concrete. The cement powder mixes with water to form paste and acts like glue, holds the aggregates together. Also, provide strength, durability and water-tightness to the concrete. Different types of cement will produce different properties of concrete. There are various type of cement, for example, ordinary portland cement (OPC) is commonly use in construction,white portland cement, high alumina cement and others.

Manufacture of cement

Important components to manufacture cement:

- Calcium Oxide (CaO)

 usually occurs naturally in form of calcareous calcium carbonate (CaCO3) [chalk & limestone]

- Silicon Dioxide (SiO2)/silica

[clay & shale]
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There are 2 ways to produce cement, dry & wet processes.

DRY PROCESS

1. Chalk & clay reduced sizes to about 75μm (less than) and mixed in the desired proportion.

2. The mixture is then dried as powder.

3. The dried powder is preheated and calcining in heat exchanges.

4. The powder is then poured into inclined rotary kiln and the temperature is increasing as the powder goes down the kiln and undergoes 2 chemical changes (calcining and clinkering).

Dry Process

WET PROCESS
Compared to the dry process, wet process has more procedures to follow. There are differences between dry and wet processes.
1. Chalk & clay reduced sizes to about 75μm (less than) and mixed in the desired proportion.

2. The mixture is mixed with water to form slurry. 

3. The slurry is poured into the inclined rotary kiln. (No preheat and calcining)

4. The powder is then poured into inclined rotary kiln and the temperature is increasing as the powder goes down the kiln and undergoes 4 chemical changes (Drying > Preheating > Calcining > Clinkering)

*Sentences underlined indicated the differences between dry and wet processes. 

Manufacturing cement

Gypsum (calcium sulfate dehydrate, CaSO4.2H2O) is added into clinker, it's function is to slow down the curing process and prevent the cement paste from hardening too fast.

Gypsum


video  below that might help you understand more about the difference between cement and concrete.