The concrete is obtained by mixing cement aggregates and water in required proportions with or without a suitable admixture.
The practical utility of concrete technology for civil engineers is to enable them to know how to stock properly the materials required for concrete and to perform different tests for concrete.
Properties of concrete:-
The concrete in the plastic state ( freshly mixed ) concrete should have the following properties.
a) workability- The concrete should have good workability. It is defined as the ease with which it can be mixed, transported and placed in position in a homogeneous state.’workability of concrete is a property that determines amount of internal work necessary to produce full compaction.’it depends upon the quantity of water , grading of aggregate and percentage of fine materials in the mix.
b) segregation :-it is defined as the breaking up of cohesion (separation of coarse aggregate) in a mass of concrete. The concrete should be free from segregation. It results in honeycombing, decrease in density and ultimately loss of strength of hardened concrete.
c) bleeding:- it is defined as the separation of water or water cement mixture from the freshly mixed concrete. The concrete should have no bleeding. It causes the concrete porous and weak.
d) harshness:-it is the resistance offered by concrete to its surface finishing. The surface of harsh concrete remains rough and porous.
The concrete in the hardened state should have the following properties:-
a) strength:-the hardened concrete should have high compressive strength so that it can resist the heavy loads of the structures. It should not be less than 15.5N/mm2.
b) durability:-the hardened concrete must be durable to resist the effect of rain, Frost action etc. This property is mainly affected by water cement ratio.
c) impermeability:-The hardened concrete should have sufficient impermeability or water tightness so that it can resist the entry of water inside the structure.
d) shrinkage:-The hardened concrete should exhibit minimum shrinkage. This property is guided by water cement ratio.
e) creep:-The hardened concrete should be subjected to minimum creep. It is the continuous strain which the concrete undergoes due to application of external loads.
f) thermal expansion:-the hardened concrete should have minimum thermal expansion so as to provide good resistance to fire.
