For the same workability and strength, concrete having large size aggregate requires less amount of cement than in concrete having smaller size aggregate. Hence, in large bulk works large-sized aggregates are preferred.

Different Size of Aggregates Used For Different Purposes

Leaser cement reduces the heat of hydration and thereby the shrinkage cracks. Use of large-sized aggregates also increases the workability of concrete. The maximum size of aggregate is also governed by the following factors:

• It should not be more than 3/4 of the clear spacing between reinforcing bars.
• It should not be more than 1/4 of the minimum thickness of the member.
• For heavily reinforced concrete members, the nominal maximum size of the aggregates should usually be restricted to 5mm less than the minimum clear distance between the main bars or 5mm less than the minimum cover to the reinforcement whichever is smaller.
• For structures like abutments, piers, retaining walls, 40mm size aggregates should be used.
• For flooring works normally 10mm size aggregate is used.
• For normal RCC works 20mm sized aggregate is used.

Read Also:

•  Functions Of Fine & Coarse Aggregate in Concrete 
•  What is Grading And Proportioning of Aggregates