Aggregates are classified into two categories according to their size:
- Coarse Aggregates These are the aggregates which has size more than 4.75 mm. In laboratories they are separated as the aggregates which are retained on the BIS test sieve no. 480. Generally broken stones are used as the coarse aggregates.
- Fine Aggregates These are the aggregates which has size less than 4.75 mm. In laboratory they are classified as the aggregates which passes through the BIS sieve no. 480. In general, Natural river sand is used as a fine aggregate.
- As per IS:383-1963 shape of the particles of the aggregates may be round, angular and flaky.. Rounded particles do not have good interlocking, where as irregular and angular particles show very good inter-locking properties. Rounded particles show good workability.
- They should have a rough surface to get better bond between particles and cement paste.
- Porosity and water absorption should be less.
- Harmful ingredients such as iron pyrites, coal, mica, shale, clay, alkali and organic impurities should be avoided. These materials should not be present in such quantities that they may effect strength and durability of the concrete. Total amount of deleterious materials in aggregates should not exceed 5%.