Construction Aggregate - Classification Based on Density of Aggregate

Fig.1.Construction Aggregate
The Aggregates can be classified based on the density of aggregates as

  1. Normal Weight Aggregate
  2. Heavy Weight Aggregate
  3. Lightweight Aggregate

Classification of Aggregates Based on Density

Normal Weight Aggregate

The normal weight aggregates are commonly used aggregates. These will include sands, gravels, crushed rocks such as granite, basalt, quartz, sandstone and limestone and brick ballasts etc.

The normal weight aggregates have specific weights between 2.5 and 2.5. These aggregates can contribute to a concrete that have a unit weight of 23 kN/m3 to 26 kN/m3 and a crushing strength at 28 days between 15 MPa and 40 MPa.

Heavy Weight Aggregate

The heavy weight aggregates have unit weights from 28 kN/m3 to 29 kN/m3. The specific gravity of these aggregates will range from 2.8 to 2.9.

Fig.2.Magnetite Heavy Weight Aggregates

The most commonly used heavy weight aggregates are Magnetite ( FeO2O3 ) and Barytes (BaSO4) and scrap iron. These are used to manufacture heavy weight concrete. The heavy weight aggregate is more effectively used as a radiation shield.

The concrete that is manufactured with the heavy weight aggregate will have a crushing strength in the range of 20 to 21 MPa. The cement - aggregate ratio will vary from 1.5 to 1.9 with a water cement ratio between 0.5 to 0.65. These aggregates will produce dense and crack-free concrete.

Limitations of Heavy Weight Aggregates

  • Heavy weight aggregates are not suitably graded
  • Heavy weight aggregates produce concrete of inadequate workability
  • Heavy weight aggregate application will result in segregation

Lightweight  Aggregate

The lightweight aggregates will have unit weight up to 12 kN/m3. These are mainly used to manufacture the structural concrete and masonry blocks for the reduction of the self-weight of the structure.

Fig.3.Expanded Clay Lightweight Aggregate

These aggregates may be natural, such as diotomite, pumice, volcanic cinder etc. These can be manufactured ones like  bloated clay, sintered fly ash or foamed blast furnace slag.

Read More About Lightweight Aggregates in Lightweight Aggregates in Construction

Features of Lightweight Aggregates 

The main features of light weight aggregates are:
  1. Low Density
  2. High water absorption
  3. Concrete is formed with lower workability
  4. Lower Modulus of Elasticity
  5. Lower Tensile Strength
  6. Rough Surface Texture
  7. High Shrinkage and Creep
Some of the important Lightweight Aggregates are:

  1. Bloated Clay: These are of size 5 to 20mm. These take spherical shape and are hard, light and porous. The water absorption is about 8 to 20%.
  2. Sintered Fly Ash: These have unit weight of 10 kN/m3. These have a porous structure
  3. Expanded Shale: These are produced by passing the crushed shale through a rotary kiln at 110 degree celsius. This is also known as herculite or haydite. These type have higher resistance to heat. This is used for the refractory lining, fire proofing of the structural steel. It has better sound absorption.