How To Select Quality Coarse Aggregate

The typical coarse aggregate size ranges from 4.75 mm to 18 mm.

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.

Aggregates need to be hard, strong, chemically inert, and non-porous.

Organic substances and dirt coating compromise the strength and durability of concrete.

Coarse aggregates should not absorb moisture by more than 10% of their weight after submersion in water for 24 hours.

If aggregates absorb water by more than 10% of their weight, they are considered as porous aggregate that are undesirable for concrete production.

Aggregates should no contain flaky and elongated particles by more than 35% of their total quantity.

Angular and fairly cubical coarse aggregate particles are desirable.

Coarse aggregate should contain various fraction sizes to ensure adequate compaction of particles, hence resulting in increased density and reduced voids in concrete.

In the majority of concrete works, aggregate sizes of 20 mm or smaller are used.

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.

It is recommended to stack different aggregate sizes to use them efficiently. 

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 pop outs.

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