Confirmed Concreting ?

Reinforced cement concrete is an outstanding invention of the mankind.
It is not not possible to think of a building  where the RCC has not been used in this form or that.
All crucial elements of a structure such as Footings,beams,columns & slab are cast in RCC.
RCC is a carefully crafted creation of concrete and steel bars .

This article brings to you preliminary discussions on materials used in concrete

What is concrete ?
Concrete is a composite material prepared with stone  & sand which is bonded by cement.

A chemical reaction which is called exo-thermic, takes place in cement in the presence of water .
The cement paste gets solidified in some time which is known as the setting time.
Whereas stone & sand are inert materials ,the  bond is created by  this cement paste

Coarse aggregate 1/2" to 3/4" mix .
Coarse aggregate 1/2″ to 3/4″ mix .
Artificial Sand or Crushed sand provides a good interlock between particles.
Artificial Sand or Crushed sand provides a good interlock between particles.
Main constituents:
Cement:

Either OPC or PPC can be used.
Ordinary Portland cement is available in grades 43  & 53 and is mostly used for all RCC works.
Portland Pozzolona cement which is of grade 33 can also be used.
Only thing which needs to be stressed here is that the PPC has a delayed setting time as compared to OPC and hence the rate of strength gain with respect to time is less.
Thus the striking off period has to be increased by at least 50% if PPC is used.
Thus the project completion period shall extend due to delay in De-shuttering activity.
But the main benefit of using PPC is that it is economical as compared to OPC .
The heat evolved is also lesser as  compared to OPC ( being of higher grades).
Thus the occurrence of micro cracks on the surface of freshly laid slab is reduced if PPC is used.

Fine aggregate ( Sand):
It can be either River sand or natural sand.

Maximum silt percentage of silt in the sand should not be more than 6%.
Due to shortage of sand, now a days, crushed sand which is also known as the artificial sand is being used.
The microscopic view of natural sand shall show rounded particles whereas that of the crushed sand shows angular particles.
The rounded particles are responsible for workability whereas the angular particles give good interlocking between particles.
Therefore a judicious combination of natural sand & crushed sand are recommended to use both of these properties.

Coarse aggregate( Stone ):
For purpose of concrete as used in a RCC building the stone size is 1/2″ to 3/4″.

The % of flaky & elongated aggregates shall be restricted as these reduce the crushing strength.

Water:

Water used in concrete should be good potable water free from acid or alkali compounds.
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