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,
- Uniformly Graded Aggregates
- Well graded Aggregates
- Gap Graded Aggregates
- Open graded
- 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
2. 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.
3. 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.
4. Open graded:
- In this type, the smaller size aggregates are present.
- Due to this, air voids are more and permeability is also more.
5. 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 gradation 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|
|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|
|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|