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:

1. Uniformly Graded Aggregates
2. Well graded Aggregates
3. Gap Graded Aggregates
4. Open graded
5. Poorly graded

Check the classification of aggregates>>>

1. Uniformly Graded Aggregates:

• 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

• Well graded Aggregates

• 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.

• Gap Graded Aggregates:

• 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. 

• Open graded:

• In this type, the smaller size aggregates are present.
• Due to this, air voids are more and permeability is also more.

• Poorly graded

• 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. 

 Grading of aggregates

• 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 gradiation of aggregates, and depend on result decision has to be made.

Grading Limits of aggregates:

Following are the grading limits of aggregates,

 Grading Limit for Coarse Aggregates: (Based on Clause 4.1 and 4.2 of IS: 383- 1970)

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

Grading Limits for Fine Aggregates: (Based on Clause 4.3 of IS: 383 – 1970)

IS Sieve Designation	Percentage Passing
	Grading Zone I	Grading Zone II	Grading Zone III	Grading Zone IV
10 mm	100	100	100	100
4.75 mm	90 – 100	90 – 100	90 – 100	95 – 100
2.36 mm	60 – 95	75 – 100	85 – 100	95 – 100
1.18 mm	30 – 70	55 – 90	75 – 100	90 – 100
600 microns	15 – 34	35 – 59	60 – 79	80 – 100
300 microns	5 – 20	8 – 30	12 – 40	15 – 50
150 microns	0 – 10	0 – 10	0 – 10	0 – 15