Aggregates- Requirements and Classification

Construction Aggregates

Aggregate constitutes the 70 -75% of the total concrete volume. These are the major material that provides a skeleton structure for the concrete. They act as economic space fillers. The aggregates are treated as chemically inert or inactive materials in the concrete.

The cost of aggregates is cheaper than the cement material. But they provide a greater volume of stability and durability for the concrete. Primarily the concrete imparts strength to the concrete in terms of bulk density. The strength of the concrete mix is increased by using aggregates of two or more sizes.

Requirements of An Ideal Aggregate

As per the Indian Code IS 383-1970, an ideal aggregate must have the following requirements:

  1. Hard, strong, durable and Stiff
  2. Must be free from any undesirable coatings
  3. The porosity is below a limit
  4. Must possess low thermal conductivity
  5. Must be angular in shape with a rough surface
  6. It must be free from organic or deleterious substances like coal, mica, shale, clay etc
  7. Must constitute natural stones, gravels, and sand

Classification of Aggregates

The aggregates can be classified based on the following criterion:
  1. Classification of Aggregates According to Geological Origin
  2. Classification of Aggregates According to Size
  3. Classification Based on density of aggregate
  4. Classification of aggregate based on Texture
  5. Classification of Aggregates Based on Gradation
  6. Classification of Aggregates based on shape

Blending of Aggregates

The blending of aggregates can be defined as the process of mixing different types of aggregates to achieve specific goals. The goals are:
  1. End result gradation at the desired value
  2. Achieving the specifications
  3. Permeability increase or decrease based on the demand
  4. Attaining the required angularity
  5. Correct out of specific material
  6. Obtain desirable gradation
  7. Economics
The blending can be carried out by using the following formula:

P = Aa + Bb + Cc + ..............

  • P = Percentage of material that is passing a given sieve for the blended aggregates A, B,C...
  • A, B, C are the percentage material that is passing the given sieve for each aggregate A, B, C...
  • a, b,c .... are the proportion/decimal fractions of aggregates A, B, C that is used in the blended aggregates.

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