CEMENT
Cement.
Cement is
manufactured by burning proportioned mixture of calcareous and argillaceous
materials at a very high temperature and then grinding the burnt mixture to a
fine powder is called as cement.
Composition of Ordinary Portland Cement
The basic ingredients
of an Ordinary Portland cement are lime in the form of calcium oxide and
alumina.
1. Calcareous materials
The materials which contain calcium or lime as their major
constituent are called calcareous materials such as lime stone marl, chalk,
shells etc.,
These
materials will provide the required proportion of calcium oxide (Cao) in the
manufacture of cement.
2.
Argillaceous materials
The materials which contain alumina as their basic
constituent are called argillaceous material such as shale, laterite etc.,
Functions of cement ingredients
1.
Lime (Cao)
It is the major ingredients of cement, so its
proportion should be carefully maintained. It makes the cement sound and its
provides strength to the cement.
2.
Silica (SiO2)
· It is an important ingredient of cement. It
provides strength to the cement.
· Silica in excess causes the cement to set
slowly.
3.
Alumina (AI203)
· It imports quick setting quality to the cement.
· Alumina in excess reduces the strength of
cement.
4. Calcium sulphate (Cas O4)
· It is present in the form of gypsum
· It helps in increasing the initial setting time
of cement.
5. Iron oxide (Fe203)
· It provides colour, hardness and strength to
cement.
· It also helps the fusion of raw materials
during manufacture of cement.
6.
Magnesium Oxide (MgO)
· This ingredient if present in small amount,
imparts hardness and colour to the cement.
· Magnesium oxide in excess make the cement
unsound.
7. Sulphur trioxide (SO3)
· If present in very small quantity, it makes the
cement sound.
· If present in excess makes the cement unsound.
8. Alkalies
· They should be present in small quantities.
· Alkalies in excess will cause efflorescence.
Different types of cement
Based on the methods
of manufacture, the cement is mainly classified as Portland and Non-Portland
cement.
Portland and
Non-partland cements are further classified as.
1. Ordinary portland cement
2. Rapid hardening cement
3. Extra Rapid hardening cement
4. Sulphate Resisting cement
5. Blast Furnace cement
6. Quick setting cement
7. Super sulphate cement
8. Portland Pozzolana cement
9. Air entraining cement
10. Coloured cement
11. Hydrophobic cement
12. Masonry cement
13. Expanding cement
14. High Alumina cement
15. White cement
1.
Ordinary Portland cement
This is commonly used cement. Out of total production, the
production of Portland cement is about 90%. It is suitable for general
construction works when there is no exposure to sulphate in the soil or in the
ground water.
2.
Rapid Hardening cement
This is Ordinary cement with increased lime
content and with very fine grinding. It consists of large percentage of
tricalcium sililcate. It attains high strength in early days. The compressive
strength at the end of one day 16 N/mm2 and at end of 3 days is above 21 N/mm?.
The curing period is short. It is also used to manufacture precast
elements. .
3.
Extra rapid hardening cement
Extra rapid hardening cement is obtained by rapid
hardening portland cement with in tergrinding calcium chloride. The concrete using
extra rapid hardening cement, the concrete pouring mustbe finished with in
about 20 minutes includes transportation, placing, compacting.
Itsstrength is about 25% higher than that of
Rapid hardening cement with in one or two days.
4.
Sulphate resisting cement
The Ordinary portland cement does not resist
sulphatic action. Hence we need a cement to rersistsulphate. They are
manufactured by adding 5 to 6% of tricalcium aluminate to ordinary cement.
It results in increase in resisting power against
sulphates. This cement is used in structures like culverts, syphons and canal
linings. It is highly resistant to sea-water.
5.
Blast Furnace cement
Portlandblast furnace cement is obtained by mixing partland
cement, clinker, gypsum and blast furnance slag in suitable proportions and
grinding the mixture. This cement has physical properties similar to those of
ordinary portland cement.
It has low heat of hydration and is better resistant to soils
and water containing excessive amount of sulphates or alkali metals. It can be
used for mass concrete structures.
6.
Quick setting cement
This cement sets very early.The early setting property is due
to the reduction in the quantity of gypsum content in the cement. This cement
is mostly used in under water construction where pumping is involved.
7.
Super sulphate cement
Super sulphate cement is manufactured by grinding together a
mixture of 80 85% granulated slag 10 to 15% of gypsum and about 5% of partland
cement clinker. If has very low heat evolution and high resistance to chemical
attack. If can be used for marine work.
8.
Portland Pozzolana cement
Pozzolana is a silicious material which is finely divided
from and in the prsence of water, react with calcium hydroxide to form
compounds possessing cementious properties. Portland pozzolana cement is made by
grinding together partland cement clinker+ 40% of pozzolana+ gypsum. It is
useful in marine and hydraulic construction and the mass concrete construction.
9.
Air entraining cement
It is ordinary portland cement mixed with small quantities of
air entrained materials such as resin, animal and vegetables fats and oil
during the process of grinding. These materials have the property of entering
more air in the concrete. The air found in the minute air bubbles distributed throughout
the mass, make the concrete more plastic and workable reduce segregation and
bleeding of concrete.
10.
Coloured cement
They are manufactured in the same way as ordinary cement and
suitable pigments 5 to 10% are added. They are used for decorative works.
11.
Hydrophobic cement
It is known as water proofed portland cement. It is made
actually from ordinary portland cement clinker. After grinding, the cement
particle is spreayed in one direction and water proofing film forming materials
such as oleic acid or stearic acid from the another direction such that every
particle of cement is coated with a very fire film of this water repellent
materials which protects them from the bad effect of moisture during strorage
and transportation.
12.
Masonry cement
Masonry cement is a type of cement which is made with such
combination of materials, which when used for making mortar, incorporates, all
the good properties of lime mortar and cement mortar. To achieve this
properties, hydraulic lime, crushing stone slag or highly colloidal clay are
mixed with ordinary cement. It is mostly used for masonry construction.
13.
Expanding cement
Concrete made with
ordinary Portland cement shrinks while setting due to loss of water. In
expanding cement the volume increases on hardening. To prepare this cement 20%
of sulpho aluminate and 15%. The cement can be used for grouting machine
foundations and prestressed concrete ducts.
14.
High alumina Cement
This cement is manufactured by clinkers formed by bauxite and
lime. It contains as high as 35 to 45% of aluminates. It sets quickly and achieves
higher ultimate strength. The com pressive strength a fter one day s 40 N m 2 and
at the end of 3 days is about 50 N/mm2. It may be used when quick strength is
required.
15.
White cement
This is an ordinary cement and free from colouring oxides
like oxides of iron & manganese. It dries quickly. It possesses high
strength. It is in white colour and used for floor finish and ornamental works.
Grades of cements
The grade of cement refers to its compressive strength in 28
days. Till around 1973 only 33 grade cement was Nowadays 43 and 53 grade
cements are available. available.
Grade 33 Strength 33 N/mm2 (As per IS 269-1989)
Grade43 Strength 43 N/mm? (As per IS 112-1989)
Grade53 Strength 53 N/ mm2 (As per IS 12269-1987)
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