Concrete is the homogeneous mixture of cement or lime, sand, aggregate and water with their proportion. The cement used in concrete is called cementing material. The sand used in the concreting is fine aggregate. The aggregate used in concrete is obtained either from stone or from over bond bricks. When the concrete mixture is allowed to cure, hard mass is formed. Classification of concrete is done into 2 parts.
The concrete is classified as following
1) According to the binding materials.
2) According to design
3) According to purposes
1)Classification of concrete according to the binding materials:
According to the binding material the concrete is classified as:
i) Cement concrete
ii) Lime concrete
i) Cement concrete:
If cement is used in concrete as a binding material work then concrete consists of cement, sand, aggregate and mixed in suitable proportion with the addition of water.
ii) Lime concrete:
If lime is used in concrete as a binding material then concrete consists of lime, sand, aggregate mixed in suitable proportion with the addition of water.
2)Classification of concrete according to design:
The concrete according to design are classified as follows:
i) Plain cement concrete(PCC)
ii) Reinforced cement concrete(RCC)
iii) Pre-stressed cement concrete(PCC)
i) Plain cement concrete(PCC):
The cement concrete in which no reinforcement is provided is called Plain cement concrete(PCC). It is sometimes called mass cement concrete. It is considerably stronger in compression but weak in tension and shear.
#Ingredients of PCC
2) Sand(Fine aggregate)
3) Coarse aggregates
# Uses of PCC
It is commonly used in the construction of the column foundation, bedrocks, massive gravity dams, heavy foundation, etc.
ii) Reinforced cement concrete(RCC) :
It is the cement concrete in which reinforcement is provided for taking tensile, excessive compressive or shear stresses.
The usual proportion of ingredients are:
Part of portland cement : One or two part of clean sand : Two to four parts of crushed stones aggregate
The steel reinforcement is generally used in the form of round bars, 6 to 32mm.
# Uses of RCC:
It is commonly used for the construction of beam, column, slabs, lintels raft of a mat foundation.
iii) Pre-stressed cement concrete:
It is the cement concrete in which high compressive stresses are artificially induced before its actual use. The high compressive stresses are induced by pre-tensioning. The reinforcement before placing the concrete is released when the final set of the concrete takes place.
# Uses of PCC:
It is used where high stresses are developed and it is uneconomical to use in ordinary reinforcement.
Characteristics of good concrete:
A good concrete should have the following characteristics:
1) It should have high compressive strength so that it can resist the heavy load of the structures. The compressive strength should not be less than 15.5 N/mm2.
2) It should have minimum shrinkage and hardening.
3) It must be adequately dense.
4) It should be economical for the desired strength.
5) The density of good concrete should be about 24kN/m3.
6) It should be durable.
7) It should have sufficient waterproofing properties.
8) It should have sufficient water impermeability or water tightness.
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