Portland cement, is a product formed by the experiments on limestone and clay. There mixture turned into hard binding material after adding water to it within few hours. The shape obtained after hardening during the experiment looked like a Portland rock of England. So the name of Portland cement became as the recognizing name of the cement mixture.
Before knowing about Portland cement there are other various cement which are used for various applications.
It is the combination of dicalcium silicate and tricalcium silicate and their ratio is maintained higher so that it withstands the corrosion by sulphate and sea water.
It is formed by the heat treatment of limestone and bauxite at temperature 1550-1600 oC. Its composition mainly contains tricalcium aluminate, dicalcium silicate and dicalcium silicate aluminate. It also has resistance towards sea and sulphate water along with improved strength.
Water proof cement:
By addition of calcium and aluminium stearates to Portland cement. The cement turns into water proof cement which it done effect with moisture present in atmosphere after hardening.
Hydraulic hydrated lime:
Calcium hydroxide is present in high concentration in this cement to use in brick mortar. It is available in lesser prices when compared with other types of cements.
For high erection of structures and for reinforced concrete mix, slag cement is used. It is formed from the clinkers of Portland cement and the slag obtained from blast furnace, blended along with small quantity of gypsum.
It is made from manganese oxide and magnesium chloride, it mainly the top user for interior floor works of a buildings. This used for absorbing sound from surrounding.
This is formed by mixing the volcanic rock or amorphous silica with Portland cement where it ratio is about 20 – 50%. It has advantage of using it in constructing underground water structures; it is not suitable to handle high temperature due slow rate of hardening.
Types of Portland cements produced:
Totally about five types of Portland cements are used for construction, and the classification is made based on the percentage of composition of each compound present in it. Ingredients ratio differs the properties like strength, heat evolution and rate of setting. The main compounds are magnesium oxide, dicalcium silicate, tricalcium silicate and tetracalcium alumina ferrite.
1) Regular Portland: It has the compositions of 40-60% tricalcium silicate, 10-30% dicalcium silicate aluminate and 7-13% of tricalcium aluminate. It becomes hard after 28-30 day, used for general construction of houses. It has subclass of quick setting cement, oil wall cement and white cement.
2) Sulphate resisting Portland: It has low fraction of tricalcium aluminate
3) Modified Portland: This has high ratio of dicalcium silicate to tricalcium silicate which can be used as sulphate resistant cement. It has a controlling parameter of heat evolution after application so that it should release heat more than 70-80 cal/ gm after a week of it setting up to 4 weeks.
4) Low heat Portland cement: It is used for massive structure construction due to low percentages of tricalcium aluminate and dicalcium silicate. Due this composition heat evolved is less and it should exceed the value of 60cal/gm after seven days and 70cal/gm after 28 days.
5) High early strength (HES) Portland cement: These are used in road construction due to its faster hardening rate because of the presence of higher concentration of components like tricalcium silicate and tricalcium aluminate. Since the mixture is grinded into fines it has high hydration rate. It becomes harder in three days.
Raw material used for manufacturing of Portland slag cement:
- Clincker (contains lime stone)
- Gypsum (contains fly ash)
- Blast furnace slag (consist of oxides of calcium, aluminum, silicon and iron)
Let’s see slag drying unit of cement industry:
Raw slag contains 10% moisture to use it in cement making; moisture content should be near 1%. We discuss here how the slag is treated in large scale. Drying unit operation is selected to remove moisture continuously from slag. Equipment called rotary drier is best suitable for drying operation.
- Rotary dryer
- Coal mill
- Belt conveyors
- Exhaust fan
- Electrostatic precipitator or dust collector
Cement is used to make concrete beam that have high capability to withhold the stress due to load carrying. With ferrocements the construction, get even better and well bonded with the wired meshing as the shear deformation can hold both static and dynamic loads. However, the cracks are the main weak points that bring down the life of the construction; they are caused by the non homogeneous mixing of concrete.