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What are Coarse Aggregates?

Coarse aggregate are used to make concrete and it occupies the bulk of its volume. The properties of coarse aggregates like its density, strength, porosity, size, texture and shape influences the physical properties of concrete and its durability.

How to choose good quality coarse aggregate in India?
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The strength of coarse aggregates depends upon the strength of the parent rock from which it is sourced. Ideally the coarse aggregates should be sourced from granite and of roughly cubical shape.

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Coarse aggregate for concrete should be well graded i.e. it should have aggregate particles of different size fractions to ensure better packing of concrete.

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In case aggregates of single size viz. 20mm,10mm are available then the same should be blended in appropriate ratio (say 60:40 or 70:30) and then used in concrete.

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Coarse aggregate should not contain any harmful chemicals like sulphates, chlorides which affect the durability of concrete.

course aggregate
How to avoid buying poor quality coarse aggregate?
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Aggregate sourced / made from low strength and porous rock is considered poor quality.

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Avoid buying uniformly graded aggregate- when coarse aggregate pieces are more or less of the same size.

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Use of elongated and flaky aggregates should be avoided as they have higher surface area as compared to cubical particles, negatively affecting workability of concrete and eventually results in increased cement demand.

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Elongated aggregates (when the length of aggregate is more than twice its width) have a tendency to break at very low compressive loads as a result the compressive strength of concrete made with such aggregates is also lower and hence their use should be avoided.