How to Choose Quality Coarse Aggregate for Concrete Construction?


The selection of good quality coarse aggregate is essential for the production of concrete that meets the desired strength and durability requirements. Ideal construction aggregate should have a rough surface texture and should be clean, strong, and free from coating and other dirt particles.

Coarse aggregates with a size of 20 mm or less are commonly used for the majority of concrete construction. One can roughly check the surface texture, particle shape, and cleanliness of the coarse aggregate just by visual observation. However, porosity and gradations require specific laboratory tests.

How to Choose Quality Coarse Aggregate for Concrete Construction?

In order to select good quality coarse aggregates, engineers should consider the following crucial points:

  1. The typical coarse aggregate size ranges from 4.75 mm to 18 mm.
  2. Gravel or broken stone aggregates with rough and non-glassy texture are the best aggregates because they create a good bond with the cement paste.
  3. Aggregates need to be hard, strong, chemically inert, and non-porous.
  4. Organic substances and dirt coating compromise the strength and durability of concrete.
  5. Coarse aggregates should not absorb moisture by more than 10% of their weight after submersion in water for 24 hours.
  6. If aggregates absorb water by more than 10% of their weight, they are considered as porous aggregate that are undesirable for concrete production.
  7. Aggregates should no contain flaky and elongated particles by more than 35% of their total quantity.
  8. Angular and fairly cubical coarse aggregate particles are desirable.
  9. Coarse aggregate should contain various fraction sizes to ensure adequate compaction of particles, hence resulting in increased density and reduced voids in concrete.
  10. In the majority of concrete works, aggregate sizes of 20 mm or smaller are used.
  11. To ensure good coarse aggregate compaction and higher concrete density, it is recommended to mix 20 mm and 10 mm coarse aggregates in the ratio of 70:30 or 60:40.
  12. It is recommended to stack different aggregate sizes to use them efficiently.  
  13. Prevent the use of friable and chert aggregates. The former is susceptible to splitting, whereas the latter has low resistance against weathering and is likely to cause popouts. 
Figure-1: Undesirable Aggregate Shape
Desirable Coarse Aggregate Shape
Figure-2: Desirable Coarse Aggregate Shape

FAQs

How to determine the aggregate quality?

Field observations and testing can be used to check the quality of aggregates and choose suitable aggregate to produce concrete. Ideal construction aggregate should have a rough surface texture and be clean, strong, and free from coating and other dirt particles.

Which type of aggregate is suitable for concrete?

 Gravel and crushed stone are suitable for making quality concrete

What is the common size of aggregate used for concrete production?

Coarse aggregate with 20 mm and smaller sizes are commonly used for the majority of concrete construction. Read more

Which shapes of aggregate are not good for concrete?

Flaky and elongated aggregate particles are not good for concrete.

Which type of aggregates gives good workability?

Rounded aggregate gives more ease of working and provides good workability. Click here to read more.

Read More

How Fine Aggregate Affects Mix Design of Concrete?

How Coarse Aggregate Affects Mix Design of Concrete?

6 Types of Deleterious Substances in Aggregate



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