What is Grading of Aggregates??

Grading of aggregates is procedure to find out the particle size distribution of various aggregates.
This method helps to determine the aggregates size and percentage used in construction works.
Coarse aggregates are graded as, 80mm, 63mm, 40mm, 20mm, 10mm
Fine aggregates are graded as. 10mm, 4.75mm, 2.36mm, 1.18mm. 600micron, 300micron, 150 micron
Basically, grading of aggregate is to find out size of specific aggregates and its retention on specific sieve size.

Classification of aggregates based on grading:

Depending on the percentage of size of aggerates present, aggregates are also classified as,

In this type of aggregates, aggregates has more prominent percentage of particular size of aggregates. Eg. Aggregates which has 16mm size of aggregates 80%, and remaining 20% is combination of rest sizes.
In uniformly graded aggregates, there will be high chances to form a void, and to fill up this void cement paste requirement is very high. Due to this concrete can be more porous.
And the changes of high permeability and low stability is there

This consists almost all sizes of particles and due to this voids in concrete is almost filled by small size aggregates and this form a compacted mass.
Due to less voids formations, this is less permeable and has high stability.
This is the most used and preferred aggregates, as it suitable for every type of construction.

In this type of aggregates, a certain size of aggregate in missing (almost has zero percentage).
This has moderate voids, and moderate permeability and low stability.
This are generally used for the construction, where economical mix is required.
This is also used when to improve aesthetic purpose.

In this type, the particular size of aggregate in much and other are very less.
Due to this, the void formation is more, stability is less and permeability is more.

The grading of aggregates is mainly depend on particle size of aggregates.
To find out the particle size distribution, sieve analysis is performed.
Grading is very important factor , which influences the strength and durability of concrete. Also this is important factor for mix design of concrete.
Before selection on sand/aggregates for construction, their sieve analysis has to be made, to find out the gradation of aggregates, and depend on result decision has to be made.

Following are the grading limits of aggregates,

IS Sieve	Percentage passing for single sized aggregates of nominal size(mm)
	63 mm	40 mm	20 mm	16 mm	12.5 mm	10 mm
80 mm	100	–	–	–	–	–
63 mm	85 – 100	100	–	–	–	–
40 mm	0 – 30	85 – 100	100	–	–	–
20 mm	0 – 5	0 – 20	85 – 100	100	–	–
16 mm	–	–	–	85 – 100	100	–
12.5 mm	–	–	–	–	85 – 100	100
10 mm	0 – 5	0 – 5	0 – 20	0 – 30	0 – 45	85 – 100
4.75 mm	–	–	0 – 5	0 – 5	0 – 10	0 – 20
2.36 mm	–	–	–	–	–	0 – 5