Cement is the most widely used materials in construction industries from decades. In India cement plants were established way back in 1904
Manufacturing of Cement –
The main raw materials for manufacturing of Portland cement are –
Lime stone and Clay – that is Calcareous and Argillaceous materials.
Cement are mainly manufactured by two process –
- Dry Process
- Wet Process.
Now a day’s mostly wet process of cement manufacturing is found which is superior to dry process.
The steps of manufacturing are as follows –
- Grinding of raw materials
Grinding of raw materials and mixing is done in the wet process as in wet condition, so finer particle and uniform mixing could be done yielding superior quality clinker. Although more fuel is consumed in wet process than in dry process.
- Mixing them in certain portion according to product required.
- Burning them in kiln at 1400 to 1500 degree Celsius temperature.
- Cooling the obtained material known as clinker and mixing it with about 2 % gypsum.
Chemical Composition of Raw Materials of Cement –
The chemical composition of raw materials used for manufacturing of cement consist of Lime, Silica, Alumina and Iron Oxide.
These compounds react chemically at high temperature in the kiln to form complex compound of cement.
Raw materials of Portland cement consists of the following chemical composition –
CaO – 60 -67%
SiO2 – 17-25 %
Al2O3 – 3-8 %
Fe2O3 – 0.5 to 0.6 %
MgO – 0.1 to 4.0
Alkalis ( K2O and Na2O ) – 0.4 to 1.30 %
SO3 – 1.0 to 3.0 %
The formed compound after chemical reaction are as follows –
Tricalcium Silicate – 3CaO SiO2 – C3S – 54.1 %
Dicalcium Silicate as 2Cao Sio2- C2S -16.6%
Tricalcium Aluminate – 3Cao Al2O3 – C3A – 10.8%
Tetra Calcium Alumino Ferite – 4 Cao Al2O3 Fe2O3 – C4AF – 9.10%
So it’s found that C3S and C2S are the main constituent and forms 70-80 % of cement.
The specification of Portland cement is specified in IS 269 –
Hydration of Cement –
When water is added to the cement the compound reacts with water and the liberating heat this process is known as hydration of cement.
C3S and C2S reacts with water and produces calcium silicate hydrate and Calcium Hydroxide.
Calcium Hydroxide is not a desirable product of cement as it is dissolved in water and may leach out from the concrete making small pores.
C3S reacts with water at more rapid pace and produces more heat and provided early strength.
C2S reacts slowly and produces less heat of hydration and is responsible for later strength of concrete.
The hydrated product of C2S are found to be more superior as they are denser.
The reaction of C3A with water is very fast and that may lead flash set to prevent this gypsum is added to cement.
C3A does not contribute to the strength of cement and makes it prone to sulphate attack.
Hydrated product of C4AF also does not contribute to the strength of cement and their hydrated product are resistant to sulphate attack.
Types of Cement –
- Ordinary Portland cement
- Rapid Hardening Cement
- Extra Rapid Hardening Cement
- Sulphate Resisting cement
- Blast Furnace Slag cement
- Quick setting cement
- Super Sulphate Cement
- Low Heat cement
- Portland Pozzolona Cement
- Air entraining cement
- Hydrophobic cement
- Masonry cement
- Expansive cement
- Oil Well cement
- High strength cement
- Redieste cement
- High Alumina Cement
Classification of cement –
IS classification –
- 33 Grade OPC – IS 269 1989
- 43 Grade OPC – IS 8112 1989
- 53 Grade OPC – IS 12269 of 1987
Grade number refers to the minimum compressive strength after 28 days.
Test of cement –
The colour should be greenish grey but it may depend upon the types of cement. No visible lumps should be there.
When hand is inserted inside the cement the hand may feel cool.
Take a pinch of cement and it should give smooth feeling
When some quantity are thrown in a bucket of water they must float for some time before they sink.
Make a cube of cement paste with about 100 gm of cement. When the cake is inserted into a bucket of water after 24 hours the cake should retain its shape.
Lab Testing of Cement
Standard Consistency Testing
Setting Time Test
Heat of Hydration Test
Chemical Composition Test.