Classification of Construction Aggregates

Anonymous March 28, 2017
Construction aggregates constitute 70 -75% of the total concrete volume. They have a major contribution towards the skeleton structure of the concrete. 

Aggregates are treated as chemically inert or inactive materials in the concrete. They act as economic space fillers. They impart strength to the concrete in terms of bulk density. This is achieved by using aggregates of two or more sizes.

Classification of Construction Aggregates
Coarse Aggregates-Gravel

The cost of the aggregates is cheaper than the cement material. But they provide a greater volume of stability and durability for the concrete. This article explores the basic requirements of construction aggregates,  their classification, and how they are blended for construction.

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 the limit
  4. Must possess a 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 criteria:
  1. Classification According to Geological Origin 
  2. Classification According to Size
  3. Classification Based on the density of aggregate
  4. Classification of aggregate based on Texture
  5. Classification Based on gradation
  6. Classification based on the 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 + ..............

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