Cement in its broadest term means any substance which acts as a
binding agent for materials natural cement (Roman Cement) is obtained
by burning and crushing the stones containing clay, carbonates of lime
and some amount of carbonate of magnesia. The clay content in such
stones is about 20 to 40 percent. Natural cement resembles very closely
eminent hydraulic lime. It is not strong as artificial cement, so it has
limited use in practice.
Artificial cement is obtained by burning at very high temperature
a mixture of calcareous and argillaceous materials in correct proportion.
Calcined product is known as clinker. A small quantity of gypsum is
added to clinker and it is then pulverized into very fine powder is known
as cement. Cement was invented by a mason Joseph Aspdin of leeds in
England in 1824. The common variety of artificial cement is known as
normal setting cement or ordinary cement or Portland cement.
Ingredients – Functions
Ordinary Portland cement contains two basic ingredients,
namely argillaceous and calcareous. In argillaceous materials,
clay predominates and in calcareous materials, calcium carbonate
predominates. Good ordinary cement contains following
- Lime (cao) ………. 62%
- silica (Sio2) ………. 22%
- Aluminca(Al2 u3) ………. 5%
- Calcium sulphate (CaSo4) ………. 4%
- Iron Oxide (Fe2 O3) ………. 3%
- Magnescia (Mgo) ………. 2%
- Sulphur ………. 1%
- Alkalies ………. 1%
Functions of Ingredients:
- Lime: Lime is the important ingredient of cement and its proportion is
to be maintained carefully. Lime in excess makes the cement unsound and causes the cement to expand and disintegrate. On the other hand, if lime is in deficiency the strength of the cement is decreased and it causes cement to set quickly
- Silica: This also an important ingredient of cement and it gives or
imparts quick setting property to imparts strength to cement.
Alumina: This ingredient imparts quick setting properly to cement.
Express alumina weakens the cement.
- Calcium Sulphate: This ingredient is in the form of gypsum and its
function is to increase the initial setting time of cement.
- Magnesia: The small amount of this ingredient imparts hardness and
colour to cement.
- Sulphur: A very small amount of sulphur is useful in making sound
cement. If it is in excess, it causes the cement to become unsound.
- Alkalies: Most of the alkalies present in raw material are carried away
by the flue gases during heating and only small quantity will be left. If
they are in excess in cement, efflorescence is caused.
Types of Cement
In addition to ordinary cement, the following are the other
varieties of cement.
a. Acid Resistance Cement: This is consists of acid
resistance aggregates such as quartz, quartzite’s, etc,
additive such as sodium fluro silicate (Na2SiO6) and
aqueous solution of sodium silicate. This is used for acid resistant
and heat resistant coating of installations of
chemical Industry. By adding 0.5 percent of unseed oil or
2 percent of ceresil, its resistance to water is increased
and known as acid water resistant cement.
b. Blast Furnace Cement: For this cement slag as obtained
from blast furnace in the manufacture of pig iron and it
contains basic elements of cement, namely alumina, lime
and silica. The properties of this cement are more or less
the same as those of ordinary cement and prove to be
economical as the slag, which is waste product, is used in
c. Coloured Cement: Cement of desired colour may be
obtained by intimately mixing mineral pigments with ordinary cement. The amount of colouring may vary from 5 to 10 percent and strength of cement if it is exceeds 10 percent. Chromium oxide gives brown, red or yellow for different proportions. Coloured cements are used for
finishing of floors, external surfaces, artificial marble, windows
d. Expanding Cement : This type of cement is produced by
adding an expanding medium like sulpho – aluminate and
a stabilizing agent to ordinary cement. Hence this cement
expands where as other cement shrinks. Expanding
cement is used for the construction of water retaining
structures and also for repairing the damaged concrete
e. High alumina Cement: This cement is produced by
grinding clinkers formed by calcining bauxite and lime.
The total content should not be less than 32 percent and
the ratio by weight of alumina to lime should be between
0.85 and 1.30.
- Initial setting time is about 31/2 hours therefore, allows more time
for mixing and placing operations.
- It can stand high temperatures.
- It evolves great heat during setting therefore not affected by frost.
- It resists the action of acids in a better way.
- It lets quickly and attains higher ultimate strength.
- It is costly
- It cannot be used in mass construction as it evolves great heat and as
it sets soon.
- Extreme care is to taken to see that it does not come in contact with
even traces of lime or ordinary cement.
f. Hydrophobic Cement: This type of cement contains admixtures,
which decreases the wetting ability of cement grains. The usual
hydrophobic admixtures are acidol napthene soap, oxidized
petrolatum etc when hydrophobic cement is used, the fire pores
in concrete are uniformly distributed and thus the frost resistance
and the water resistance of such concrete are considerably
g. Low Heat Cement: Considerable heat is produced during the
setting action of cement. In order to reduce the amount of heat,
this type of cement is used. It contains lower percentage of tri
calcium aluminates C3A and higher percentage of dicalcium
silicate C2s. This type of cement is used for mass concrete works
because it processes less compressor strength.
h. Pozzuolona Cement: Pozzuolona is a volcanic powder and the
percentage should be between 10 to 30.
- It attains compressive strength with age.
- It can resist action of sulphates.
- It evolves less heat during setting.
- It imparts higher degree of water tightness.
- It imparts plasticity and workability to mortar and concrete
prepared from it.
- It offers great resistance to expansion
- It possesses higher tensile strength
- Compressive strength in early days is less.
- It possesses less resistance to erosion and weathering action.
i. Quick Setting Cement: This cement is prepared by adding a
small percentage aluminum sulphate which reduce the
percentage of gypsum or retarded for setting action and
accelerating the setting action of cement. As this cement hardness
less than 30 minutes, mixing and placing operations should be
completed. This cement is used to lay concrete under static water
or running water.
j. Rapid Hardening cement: This cement has same initial and
final setting times as that of ordinary cement. But it attains high
strength in early days due to
- Burning at high temperature.
- Increased lime content in cement composition.
- Very fine grinding
1.Construction work may be carried out speedily.
2.Formwork of concrete can be removed earlier.
3.It is light in weight.
4. It is not damaged easily.
5. This cement requires short period of curing.
6. Use of this cement also higher permissible stresses in the
7. Structural member constructed with this cement may be
k. Sulphate Resisting Cement: In this cement percentage of
tricalcium aluminates is kept below 5 to 6 percent and it results in
the increase in resisting power against sulphate. This cement is
used for structure which are likely to be damaged by sever
alkaline condition such as canal linings, culverts, siphons etc.
l. White Cement: This is a variety of ordinary cement and it is
prepared form such raw materials which are practically free from
colouring oxides of Iron, manganese or chromium. For burning
of this cement, oil fuel is used instead of coal. It is used for floor
finish; plaster work, ornamental works etc.
Uses of Cement:
- Cement mortar for masonry work, plaster, pointing etc
- Concreter for laying floors, roofs and constructing lintels,
beams, weather sheds, stairs, pillars etc.
- Construction of important engineering structure such as
bridges, culverts, dams, tunnels storage reservoirs, light
houses, deckles etc.
- Construction of water tanks, wells, tennis courts, septic tanks,
lampposts, roads, telephone cabins etc.
- Making joints for drains, pipes etc.
- Manufacture of pre cast pipes, piles, garden seats, artificially
designed urns, flowerpots, etc dustbins, fencing posts etc.
- Preparation of foundations, watertight floors, footpaths etc.
Admixtures – Uses.
These are the ingredients or substance, which are added to
concrete to improve its properties like strength, hardness, water
resisting power, workability etc. Many admixtures like alum etc are
commonly used for this purpose.