Natural aggregates are available in the crushed or uncrushed state such as sand and gravel or stones. They are usually derived from natural sources like river terraces, riverbeds, glacial deposits or rocks and boulders.
Aggregates are classified as per shape, size and according to their nature of formation.
Round shaped aggregates, irregular or partly round shaped aggregates, Angular shaped aggregates, and flaky shaped aggregates are the shape wise classification of aggregates.
You would like to know about the shape wise classification of aggregates in detail:
Fine aggregates and coarse aggregates are the size wise classifications of aggregates.
Natural aggregates and artificial aggregates are the classification of aggregates according to their nature of formation. We already disused about the classification of aggregates according to their nature of formation.
Aggregates play a significant role in construction. They are used in the production of concrete. The total volume of concrete normally consists 75% to 85% volume of aggregates that makes the cost of concrete relatively low. Aggregates act as structural filler in the concrete. Hence it is very vital to consider the qualities, as well as properties and gradation of aggregates before carry out concrete mix design.
Qualities of Aggregates
Aggregates used for concrete should possessthe following qualities,
- 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 substances.
- If possible, flaky, scoriaceous (cinders, slag) 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.
Basic properties of aggregates mainly depend upon its physical properties and the properties of the parent rock.
Basic Properties of Aggregates
The aggregates should generally possess the following properties,
| Basic Properties of Aggregates depend upon the properties of parent rock, i.e. Igneous, sedimentary, metamorphic rock | Basic Properties of Aggregates depend upon the physical properties of natural aggregate |
| Chemical and mineral composition of parent rock | Physical soundness |
| Specific gravity of the parent rock | Shape & textures of aggregates |
| Hardness of parent rock | Size of aggregates |
| Strength of parent rock | Gradation of aggregates |
| Thermal properties of aggregates | Bulk density |
| Porosity and Water absorption | Bulking of aggregates |
| Chemical soundness | Frost attack |
| Deleterious substance | Maximum size of aggregates |
| Aggregates containing reactive silica | Segregation and breakages |
| Pore structure of parent rock |
Before selecting the aggregates for concrete, it is very important to know all the above properties. They will help you to get the better quality of concrete. Aforementioned properties of aggregates can be evaluated by carrying out the various test on aggregates.
The aggregates should be tested for their suitability, strength, toughness, hardness, shape, and water absorption.
Following are the list of tests carried out on aggregates.
- Crushing Test on Aggregate
- Abrasion Test on Aggregate
- Impact Test on Aggregate
- Soundness Test on Aggregate
- Shape Test on Aggregate
- Specific Gravity and Water Absorption Test on Aggregate
- Bitumen Adhesion Test on Aggregate
Remember that properly tested aggregates always results in a good quality of concrete. Nowadays use of concrete is increased day by day which increases the demands of aggregates. To meet these needs of the construction industries, concrete experts carry out research on concrete and developed the new artificial aggregates. These new aggregates have almost same properties as natural aggregates. People are moving towards the trends of green building, in which, artificial aggregates plays a key role to make the concrete sustainable.