28-12-2012, 06:34 PM
Micro Structure of Concrete
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Definition
Concrete:
Concrete is a heterogeneous mixture of cement, sand, aggregate and water. In which the space between the aggregates are filled with sand and the space between the sand particles are filled with cement.
Micro Structure of Concrete:
The type, amount, size, shape and distribution of different phases present in solid concrete is known as microstructure of concrete.
Aggregate Phase of Concrete
Aggregates phase is predominantly responsible for the density, modulus of elasticity and dimensional stability of concrete.
The above properties of concrete mainly depends on the physical property of aggregates.
The chemical or mineralogical properties of an aggregate has very less importance in concrete.
What is cement ?
Cement is a mixer of lime, silica, alumina and iron oxide. These raw materials are mixed intimately in definite proportions and burned at 1450 ºc to form clinker.
The clinker is then pulverized into fine particles of cement with some gypsum added to it.
Influence of compound composition on properties of cement:
It is observed that C3S contributes most of the strength development during the first four weeks.
C2S has been found to become active and contribute to strength from four weeks onwards.
Pure C3S and C2S have been found to have a strength of about 70 MPa at the age of 18 months, but at the age of 7days C2S has no strength while the strength of C3S is about 40 MPa.
C3A and C4AF has no significant effect on strength of cement.
*Ref : A.M. Neville
Hydration of cement
The unhydrated cement mixed with water indulges reactions by virtue of which the cement get hydrated and behaves as a bonding agent.
Now as the time proceeds the product of hydrations will give a firm and hard mass which is called hydrated cement paste.
Conclusion:
The progress in the field of science has put lot of possibilities for improving the internal properties of materials.
Since the concrete is heterogeneous both at micro and macro level change in internal property of a concrete microstructure will result in modified concrete which will be stronger and more durable.