Classification of coarse aggregate based on shape

June 28, 2017
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What is an Aggregate?

Aggregates are the essential constituents of the concrete which offer the body to the concrete and furthermore diminish shrinkage. Aggregate possess 70 to 80 % of volume in the concrete. The aggregate gives the maximum strength for the concrete.

Classification:

The aggregates are classified into many different types here we are going to see only about the different shape of aggregate.

Classification based on shape:

There are different type of shape available in aggregate and they are listed below

  • Rounded aggregate
  • Irregular or partly rounded aggregate
  • Angular aggregate
  • Flaky aggregate
  • Elongated aggregate
  • Flaky and elongated aggregate

Rounded aggregate:

The aggregate with rounded form has the minimum proportion of voids starting from 32% to 33%. It offers minimum surface area of extent to given volume and hence needs minimum water for lubrication purpose. It offers sensible workability for the given quantity of water and hence it requires less cement for a given water cement proportion. The sole disadvantages is that the interlocking between its particles is a smaller amount and hence the event of bond is poor. This is often why rounded aggregate isn’t appropriate for high strength concrete and for pavements subjected to tension.

Fig: Round shaped aggregate

Irregular or partly rounded aggregate:

The aggregate with irregular form has higher share of voids starting from35% to 37%. It provides lesser workability than rounded aggregate for the given water content. Water demand is higher and hence additional cement is required for constant water cement ratio. The interlocking between mixture particles is best than rounded mixture however not capable be used for high strength concrete and pavements subjected to tension.

Fig: irregular or partly rounded aggregate

Angular aggregate:

The aggregate with angularity has the most share of void starting from 38% to 45%. It needs additional water for lubrication and therefore it offers least workability for the given water cement ratio. For constant water cement ratio and workability the necessity of cement increase. The interlocking between the combined particles is that the best and therefore the event of bond is extremely smart. This can be why angular mixture is extremely appropriate for top strength concrete and for pavements subjected to tension.

Fig: Angular aggregate

Flaky aggregate:

The aggregate is called to be flaky once its least dimension is a smaller amount than 3/5th or 60% of its mean dimension. Mean dimension is that the average size through that the particles pass and also the sieve size on that these are maintained. as an example, mean size of the particles passing through 25 mm sieve and maintained on 20 mm sieve is (20+25)/2=22.5 mm. if the smallest amount dimension is a smaller amount than 3/5 x (22.5) = 13.5 mm, then the fabric is classed as flaky. Flaky combination tends to be minded in one plane that affects the durability.

Fig: Flaky aggregate

Elongated aggregate:

When the length of the aggregate is greater than the other 2 dimensions then it’s referred to as elongated aggregate or the length of the aggregate is bigger than 180% of its mean dimension it is called elongated aggregate.

Fig: Elongated aggregate

Flaky and elongated aggregate:

When the aggregate length is more than its breadth and breadth is more than its thickness then it’s aforementioned to be flaky and elongated aggregates. The higher than three varieties of aggregates don’t seem to be appropriate for concrete mix. These square measure usually obtained from the poorly crushed rocks.

Fig: Flaky and elongated aggregate

 

 

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