CLASSIFICATION OF AGGREGATE BASED ON SHAPE

CLASSIFICATION OF AGGREGATE BASED ON ITS SHAPE

Aggregate plays very important role in strength contribution in concrete. The strength of concrete also based on different shape of aggregate. Workability of concrete also affect by the shape of aggregate. Based on aggregate particle shape it may be classified as per below.

1. Round Aggregate
2. Irregular Aggregate
3. Angular Aggregate
4. Flaky Aggregate
5. Elongated Aggregate

1. Round Aggregate


  • Fully erode by water or shaped by abrasion (attrition).
  • It contains minimum voids range from 32% to 33%.
  • It gives minimum ratio of surface area to volume, thus requiring minimum cement paste to make good concrete.
  • It gives good workability.
  • They require lesser amount of water so W/C ratio is low and it makes dense concrete.
  • It has poor interlocking between particles hence the bond strength is weak to make desirable strength of concrete.
  • Examples are, River or seashore gravel, desert sand and wind blow sand.


2. Irregular Aggregate


  • It is naturally irregular or partially shaped by abrasion and erosion.
  • It contains higher percentage of voids in range between 35% yo 38%.
  • It requires more cement paste to achieve desirable workability.
  • The interlocking between particles are better than the round aggregate hence bond strength is slightly higher than round aggregate.
  • It has round edges.
  • Examples are pit sand and gravel, cuboid rock.
3. Angular Aggregate


  • The angular aggregates consist well defined edges formed at the intersection of roughly planar surfaces and these are obtained by crushing the rocks. 
  • It contains maximum percentage of voids range between 38% to 40%.
  • They requires more cement paste to make workable concrete of higher strength than required by round aggregate.
  • The interlocking between particles is good hence it provides good bond strength.
  • It makes high strength concrete. 
  • Examples are crushed rocks of all types.
4. Flaky Aggregate


  • The aggregate whose thickness is smaller than 0.6 (60%) of its mean dimensions (width and length) is termed as flaky aggregate.
  • They reduces workability of concrete.
  • The flaky aggregate particles also adversely affect on the durability of concrete as they tend to be oriented in one plan with water and air voids forming underneath. Hence they also reduces strength of concrete.
  • The presence of these type of aggregates should not be more than 15% in mass of aggregates.
  • Examples are, Laminated rocks.
5. Elongated Aggregate


  • The aggregate whose greatest dimension (length) is greater than 1.8 (180%) of its mean dimensions is termed as elongated aggregate.
  • They reduces workability of concrete.
  • The elongated particles also adversely affect the durability of concrete and strength of concrete.
  • the presence of these type of particles should not be more than  15% in total mass of aggregates. 
  • Examples are, Laminated rocks.

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