For RCC structure, torsion bars are used and due to this, bonding between
cement and the steel is good
Torsion bars used in RCC are 8/10/12/16 mm
Round bars used for RCC are 6 mm.They are flexible hence used for square
To increase tensile strength we use mild steel bars
in cement concrete. Steel bars used in cement concrete
provide good strength to the structure.
Usually steel bars are roughened or corrugated to further
improve the bond or cohesion between the concrete and
steel. Care must be taken that there should be no joints in
steel bars used for RCC work. Therefore you might have
observed that steel used for RCC work is long in length. If
full length steel bars are not available, proper overlap
should be given in steel bar and overlap should be
A care must be taken that steel should not disturb during
concreting. Steel rods should be properly binded and
proper planks or plates must be provided for walking.
RCC structure -
The vertical members supporting the beams are called
The peripheral horizontal members supporting the slab are
The beams at ground level or plinth level (the lowermost
habitable level) are called 'Plinth Beams'.
The system below ground transferring the entire load
of the structure to the soil is called 'Foundation'.
Foundation is in direct contact with soil and transmits load of complete structure
to soil. If foundation is weak then there is danger that walls will collapse or tilt
due to load of the structure.
Generally foundation is below the ground level. Depth of foundation depends on
type of soil and its bearing capacity, depth of ground water table and the size of
To allow removal of top loose soil and variation in ground level, the best
recommended depth of foundation is from 1.00 meter to 1.5 meter from original
A The flat ceiling of a story is called a 'Slab'.
Cement is a fine, soft, powdery-type substance.
It is made from a mixture of elements that are found in
natural materials such as limestone, clay, sand and/or
shale. When cement is mixed with water, it can bind
sand and gravel into a hard, solid mass called concrete.
What is Cement Æ
Manufacturing of cement :
Cement is made from calcium oxide, aluminum
oxide, silica, and iron oxide. Calcium (which is the main
ingredient) can be obtained from limestone, whereas
silicon can be obtained from sand and/or clay. Aluminum
and iron are required in small amount and can be extracted
from bauxite and iron ore. Following are the steps in
1.Mixture of limestone, sand, aluminum oxide and iron oxide
is powered and is heated in the furnace.
2.Water present in these materials gets evaporated and the
material comes to the melting stage. This partially molten
material combines together.
3.The material that comes out of the furnace is
large, glassy, red-hot cinders called "clinker".
4.After cooling the clinker, its powder is made. This is called
as Portland cement.
When cement is mixed with water, its molecules form
bond with each with the help of water. Because of this
chemical bond, the cement gets hardened. Cement is
always used to join two things. Concrete is made by
mixing sand and gravels in the cement. Cement holds
together gravels tightly and the block become a like a
stone, though the quantity of cement is less, the
concrete become like a stone.
Cement must be stored in dry place. If it gets wet due
to water or humidity in storage then we cannot used it
again by drying it.
How cement gets it
Mortar and concrete:
Cement is used to join the small stones
together. In this process the gaps between this
mixtures is filled using cement. To reduce the cost
of cement different small sized stones
(sand, grovel) are used. The mixture of cement and
sand is called as mortar. The mixture of
cement, sand and gravel is called as concrete.
Concrete becomes strong as the stones are joined
to each other.
Characteristics of cement:
Once chemical reaction is complete then cement is durable
Cement never gets rusted or rotten in normal environment.
Cement concrete is strong in compression but weak in
tension. Therefore steel is used in the concrete in places
with tension. This is called as R.C.C (Reinforced Cement
Concrete). For e.g columns and slabs in multistoried
There is no effect of normal heat on cement concrete or it
never catches fire. But it gets cracked in big fire.
Cement is bad conductor of electricity or heat.
If water contains in cement mixture is more then after
curing, hollows spaces are formed and cement becomes
Strength of the cement is more if its density is more.
Curing and Drying :
Cement powder solidifies due to the reaction of water
on it. Therefore if sufficient water is not available while
using the cement, this process will not get completed
and it will not get solidified. Therefore for first 20 days
cement should be kept wet. This is called as curing.
If excess water is used immediately after applying the
cement then small cement particles will washed away.
Therefore on the first day of the construction, care
should be taken that the cement will remain wet.
Further during the process of solidification, cement
needs water but outside air will dry it quickly.
Therefore it is necessary to give sufficient water.
Curing takes place quickly if temperature is more.
Strength increases with
Time required for curing Strength of concrete
0 Days 50 %
1 Days 61 %
7 Days 85 %
14 Days 92 %
20 Days 100 %