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Aggregates are granular substances that form 70 to 80 percent of the total volume of the

concrete. They are hard and inert substances that are free from any kind of chemicals or

adhesive of clay. Aggregates include sand, gravel and crushed aggregates like stone chippings or

crushed stone. These are available naturally in the form of a homogeneous bulk product. Sieve

analysis is done to classify and grade the aggregates into different categories.

Aggregates are classified into two broad categories, namely

1.Fine aggregates

2.Coarse aggregates

What are Fine aggregates?

These are the particles that can pass through a ?-inch sieve and their particles mainly consist of

natural sand or crushed stone. Fine aggregates have a rounder shape as compared to coarse

aggregates. These are used to fill the voids in the coarse aggregates and are used as a

workability agent in the concrete.

What are Coarse aggregates?

Coarse aggregates are particles that cannot pass through a ?-inch sieve and the aggregates

consist of gravel, cobble and boulders. These are used in concrete along with crushed stone.

The size of aggregates differs from 40 mm to 20 mm. The 40 mm aggregate is used for Plain

Cement Concrete (PCC) and 20 mm is used for Reinforced Cement Concrete (RCC). Coarse

aggregates are used for the construction of roads, and for that, the aggregate must possess the

following qualities

?Strength

?Hardness

?Toughness

?Durability

?Adhesion with bitumen

?Shape

Differences between fine aggregates and coarse aggregates

Factors	Fine aggregates	Coarse aggregates
Definition	These are small filler materials used in construction to fill the voids.	These are large filler materials used in construction.
Shape	These are spherical.	These are cubical or flaky.
Size	These are smaller and can pass through a ¾-inch sieve. These are less than 9.55 mm in diameter.	These are larger and cannot pass through a ¾-inch sieve. Their diameter ranges from 9.55-37.5 mm.
Raw materials	It is made using sand, stone screenings, burnt clay, surki, fly ash, cinders and others.	It is made using broken bricks, gravel, pebbles, broken stones, clinkers, cinders among others.
Source	It is divided into three categories based on the source, uncrushed gravel, crushed gravel and partially crushed gravel.	It is divided into three categories, namely natural rock disintegration, crushed gravel or stone and dolomite aggregates.
Function	It is used to fill the void between the coarse aggregates in the concrete.	It is used as a filler material in concrete.
Surface area	Their surface area is higher.	Their surface area is lower.
Usage	These are used in mortar, concrete, plaster, filling the voids in coarse aggregates, and filling of layers in roads.	These are used in concrete and railway track ballast.