Which are the different components of concrete?
Concrete is made up of fine and coarse aggregate, cement and water. The proportion of these components determine the strength attained and the quality of the resultant concrete.
Functions:-
Aggregates
Fine and coarse aggregate are both natural materials which are much cheaper than cement.
These are components add volume to concrete mix, and being cheap raw materials, the economy is maintained.
Also, it is important to note that, the compressive strength of aggregate is much greater than that of cement - water paste in concrete. Thus they contribute greatly to the strength of concrete.
Concrete is made up of different materials of varying size. This is done so that the variation in size compliments the void created by the other. For example, coarse aggregate leaves void spaces between them which are ideally filled by fine aggregates. In a complex mix design more than one fine and coarse aggregate may be used to achieve greater strength.
Fine aggregate
These are particles which pass through 4.75 mm sieve or in other words smaller than 4.75 mm
Generally used fine aggregates are sand and crushed stone.
Plastering mortar only have fine aggregate, as they provide a much smoother finish.
They are also used for tiling and brick laying.
Coarse aggregate
Particles which are retained on a 4.75 mm sieve is categorised as coarse aggregate.
For normal concrete 20 mm or 40 mm aggregates are used.
They generally are the highest portion in a concrete and also contribute for the highest strength.
They need lesser quantity of cement water paste as they have smaller surface area, thus contributing to higher strength of the mixed concrete.
It is worth noting that water cement paste is used as a binder, but strength wise they are the weakest link. Bigger size aggregate means less water cement paste, thus a higher strength concrete.
Cement
According to Wikipedia, a cement is a binder, a substance used for construction that sets, hardens and adheres to other materials to bind them together.
Functions:-
Cement binds the materials in a concrete.
Cement being very fine, easily fills all the void areas between aggregates and binds different particles of aggregate when it hardens.
Cement easily adheres to the rough surface of the aggregates and steel in RCC thus holding them in place.
Water
Cement in dry state does not have binding properties.
It is when cement and water is mixed that cement attains its binding properties through a process called cement hydration.
Water/Cement ratio is the most important factor which affects both the quality and strength of concrete. I have talked about water - cement ratio much elaborately in my blog Water - Cement Ratio.
A good understanding of functions and properties of different material components in concrete will help prepare a concrete which will attain the necessary strength and quality, in a economical way.
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