Cement is a mixture of different constituents and acts as the main constituent in concrete, Egyptians first manufactured Cementing materials by burning gypsum. And then Romans & Greeks used cementing materials obtained by burning limestone.
Do you know?
Romans added blood & milk to increase the workability of mortar?
The fact that, hemoglobin acts a plasticizer which helps in increasing workability. But later, they found that it decreases durability.
Romans found the fact that volcanic ash & tuff, when mixed with limestone, gives superior mortar which has a high quality. (The early signs of making concrete.) Since then, they started experimenting by adding different materials in the mix to increase the workability of mortar.
The Portland cement was first manufactured by Joseph Aspdin who is a bricklayer and builder. He took the patent for Portland cement on 21st October 1824. Since then, continuous efforts were made on cement and found that changing chemical compositions in cement exhibit different characteristics and properties. With the high demand for cement, for widely varying conditions, the types of cement that could be made only by varying the relative proportions of the oxide compositions were not found to be sufficient. Experiments have been taken to add new materials to the cement known as additives., at the time of grinding or by changing basic raw materials during the manufacture of cement. The use of additives, changing chemical composition and use of different raw materials have resulted in the availability of many types of cement.
Cement is primarily characterized into two types:-
- Hydraulic cement
- Non-hydraulic cement.
The cement which hardens in the presence of water. because of Hydration (The chemical reaction between cement and water )This type of cement can also harden in underwater. Portland cement is the best example for hydraulic cement.
Non Hydraulic cement:
The cement which doesn’t harden underwater is called non-hydraulic cement. This type of cement hardens when it reacts with the atmospheric carbon dioxide (carbonation). This cement is resistant to attack by chemicals after setting. Non-hydraulic cement is manufactured using non-hydraulic lime, gypsum plasters and oxychloride, which has liquid properties.
14 Different types of cement :-
1. Ordinary Portland Cement (OPC):
This is the most common type of cement which is extensively used. It has good resistance to cracking and dry shrinkage but less resistance to chemical attack. OPC is not suitable for the construction work which is exposed to sulphates in the soil.
Ordinary Portland cement is available in following types
33 grade, 43 grade & 53 grade.
The grade represents the strength of cement at 28days. 33grade = 33N/mm2
2. Rapid Hardening cement:
Rapid hardening cement is very similar to ordinary Portland cement (OPC). The early strength is achieved by adding excessive C3S in the mix and by lowering the C2S content in the cement. As the name itself resembling that, this type of cement is used where there is a need for high early strength. Ex. Pavements, busiest roadways
The strength of Rapid Hardening cement at age of 3 days is almost same as the 7 days strength of Ordinary Portland cement. It requires same water-cement ratio as OPC. This type of cement is not used for massive concrete constructions.
3. Low heat portland cement: –
This type of cement is manufactured by lowering the C3S content and increasing the C2S content. It possesses less compressive strength than ordinary Portland cement. It has less lime content than OPC. This type of cement is mostly used in the construction of retaining walls and it is strictly not suitable for thin concrete structures.
4. Sulphate Resisting Portland Cement:-
It is manufactured by keeping the percentage of C3A below 5%. This type of cement is used where the structure is prone to severe sulphate attacks(alkaline conditions) such as construction in the foundation of soil, marine conditions, sewage treatment tanks.
5. High alumina Cement:-
This type of cement has rich alumina content about 35% which helps in gaining ultimate high strength within a short period. This type of cement is used where a structure is subjected to the action of sea water, chemical plants and furnaces.
6. Blast furnace slag cement:-
This type of cement is cheaper than Ordinary Portland cement. it is manufactured by intergrinding of OPC clinker and blast furnace slag. Blast furnace slag cement develops low heat of hydration and has less early strength.
7. Coloured Cement:-
This type of cement is also known as Colcrete. It is manufactured by adding coloring pigment to the OPC. it is used in joining tiles.
8. Pozzolana cement :-
The pozzolana is a material which is formed due to the volcanic eruptions. It is a siliceous material having about 80% clay in it. Pozzolana cement is manufactured by mixing 30% of pozzolana to Ordinary Portland cement clinkers. This type of cement is used in construction of dams and weirs.
9. Air-entraining cement:-
This type of cement is manufactured by adding 0.025–0.1% of air entraining agents to the ordinary Portland cement clinker. Air entraining agents are generally made up of wood resins, calcium agents, vegetable oils and animal fats.
10. Hydrophobic cement:-
This type of cement is manufactured by grinding ordinary Portland cement clinker with water oleic acid or stearic acid. These acids forms as a water repellent film around the cement particle which increases the shelf life of cement. The formed around each grain of cement reduces the rate of deterioration of the cement during long storage, transport, or under unfavourable conditions. The film is broken out when the cement and aggregate are mixed together at the mixer exposing the cement particles for normal hydration.
11. Expansive cement:-
This type of cement is manufactured by adding stabilizer which stabilizes the cement to expand. This can be achieved by adding 8-20% of sulphoaluminate & 15% of stabilizer to the ordinary Portland cement clinker.
Concrete made up of OPC shrinks while setting due to loss of free water. Concrete also shrinks continuously for a long time. Cement used for grouting should not shrink or change volume for this, we use expansive cement. the expansive cement doesn’t show any volume change after hardening.
12. White Cement:-
This type of cement is obtained by lowering the iron oxide content in the Ordinary Portland cement. The strength and durability is same as OPC. This type of cement is used for joining tiles and other interior works.
13. Waterproof portland cement:-
This type of cement is manufactured by adding small percentages of metal sereates in OPC during grinding. This type of cement is used in foundations, water tanks & other water retaining structures.
14. Oil-well Cement:-
In order to extract oil from the stratified sedimentary rocks, Oil wells are dug to a greater depth. For safe pumping out of extracted oil steel casing is inserted. It is likely that if oil is struck, oil or gas may escape through the space between the rock formation and steel casing. To fill this space Oil well cement is used. Oil well cement is manufactured by adding retarders (Starches or cellular products) to Ordinary Portland cement.