Basically, aggregates are crushed or uncrushed materials such as sand, gravels or stones, derived from the natural sources like river terraces, riverbeds, glacial deposits or rocks and boulders, for use in the production of concrete for structural purposes including mass concrete works. Aggregates are available in different types depending on their uses.
Aggregates act as a structural filler in the concrete. It can also affect the appearance of the cast surface which is a very important consideration in concrete mix design.
Also Read: Do’s & Don’ts While Concreting
Normally the total volume of concrete consists of 75% to 85% volume of aggregates that makes the cost of concrete relatively low.
Aggregates used for concrete should possess the desirable qualities such as,
- It should be clean, hard, strong, durable and free from any matter that might affect the quality of concrete.
- It should be free from veins, adherent coating, Injurious Amounts of disintegrated pieces, Alkali and other deleterious.
- As far as possible, flaky, scoriaceous and elongated pieces should also be avoided.
Aggregates are extremely important to understand in terms of how their properties affect the properties of fresh and hardened concrete. The properties of aggregates have a significant impact on the workability, shrinkage, strength and durability.
The Aggregates should Generally Possess the following Properties,
01. Depending Upon Properties of Parent Rock:
- Chemical and mineral composition of parent rock
- Petro-graphic description
- Specific gravity of the parent rock
- Hardness of parent rock
- Strength of parent rock
- Thermal properties of aggregates
- Porosity and Water absorption
- Chemical soundness
- Deleterious substance
- Aggregates containing reactive silica
- Pore structure of parent rock
02. Depending Upon Physical Properties of Aggregates:
- Physical soundness
- Shape & textures of aggregates
- Size of aggregates
- Gradation of aggregates
- Bulk density
- Bulking of aggregates
- Frost attack
- Maximum size of aggregates
- Segregation and breakages