Aggregates are classified depending on the shape and size of the aggregates as follows,
Types of construction aggregates
Classification based on size of aggregates:
1. Coarse Aggregates:
- Coarse aggregates are the aggregates which are greater than 4.75mm and cannot pass through 4.75mm or can retain on 4.75mm size sieve.
- The usual range of coarse aggregates are 9.5mm to 37.5mm.
- Coarse aggregates can be as large as 80mm in size to.
- Generally, the most common size of coarse aggregates which used in construction is 10mm, 20mm, 40mm.
- The large aggregates size reduces the quantity of cement and water needed.
- Coarse aggregates can be naturally occurring gravels (typically for size 40mm and more) or it can be extracted from rock for particular size of aggregates (specially for 10mm, 20mm size)
- Depending on grain size, coarse aggregates also classified as,
|Fine gravel||4mm – 8mm|
|Medium gravel||8mm – 16mm|
|Coarse gravel||16mm – 64mm|
|Cobbles||64mm – 256mm|
Depending upon the density of rock, coarse aggregates are also classified into
- Ultra-light weight aggregates
- Light weight aggregates
- Medium weight aggregates
- High density aggregates
- Standard Aggregates
These aggregates have different densities depending on parent rock and type of rock.
2. Fine Aggregates:
- Fine aggregates are the aggregates which are less than 4.75mm and can pass through 4.75mm or cannot retain on 4.75mm size sieve and retain on 0.15 mm sieve
- The usual range of fine aggregates are 0.06mm to 4.75mm.
- They include crusher dust, fine sand, manufactured sand, etc.
- Fine aggregates sand or crushed stone that are less than 9.55mm in diameter.
|Fine Aggregates||Size variation|
|Coarse Sand||2.0mm – 0.5mm|
|Medium sand||0.5mm – 0.25mm|
|Fine sand||0.25mm – 0.06mm|
|Silt||0.06mm – 0.002mm|
Fine aggregate are further classified into the two categories depending their occurrence,
a. Natural sand:
- Natural sand is sand which is naturally available, generally river sand. River sand consist grading of all size including coarse sand, fine sand, silt and clay.
- Natural sand is very good for plastering, as it well graded sand.
b. Crushed sand/ M sand
- Crushed sand is sand which manufactured by crushing the rock. Crushed sand is generally uniformly graded sand, as it consists of uniform size of sand. and also Known as Manufacturing sand or M sand.
- Crushed sand it very good and popular in construction as it is readily available, less expensive than natural sand.
- Extraction of natural sand from river damages the ecosystem of river and extraction more than limit is prohibited and illegal. Just because of this crushed sand is widely used in construction industry.
- Crushed sand is manufactured so that some properties of sand can be pre-planned before manufacturing such as size, shape, density etc.
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Classification based on shape of aggregates:
Based on the shape of aggregates it can be further classified into following
- Rounded Aggregates
- Irregular aggregates
- Angular aggregates
- Flaky aggregates
- Elongated Aggregates
- Flaky & elongated aggregates
1. Rounded Aggregates:
- Rounded aggregates are aggregates which available naturally. Due to friction, climate the aggregates get eroded and they get the round shape.
- Rounded aggregates offer a better workability to concrete on site.
- They need lesser water cement ratio to form a concrete. But it has rounded surfaces and this why they do not form a good bond in concrete. And hence gives lesser strength to concrete. For this reason, rounded aggregates are not so much in use in construction, especially for high strength concrete.
2. Irregular aggregates:
- Irregular aggregates have uneven edges and shape, and so that form a very good bond in concrete and gives higher bond strength and mechanical strength to concrete.
- It gives lesser workability to concrete on site.
- These aggregates can be naturally occurring on manufactured according to need.
3. Angular aggregates:
- Angular aggregates have even, well defined edges and shape.
- This can be formed by crushing of rocks.
- It gives lesser workability to concrete on site. But form a stronger bond with concrete.
- It enhances the compressive strength of concrete by 10-20% in many cases. Hence it is used widely in construction.
4. Flaky aggregates:
- Aggregates are called Flaky aggregates when its thickness is very small compared to its width and length. Or in other word, the least dimension of aggregate is less than 60% of its mean dimension.
5. Elongated Aggregates
- Aggregates are called Elongated aggregates when its length is larger as compared to its width and length. Or in other word, the length of aggregate is greater than 180% of its mean dimension.
6. Flaky & elongated aggregates:
- Aggregates are called Flaky & Elongated aggregates when its length is larger than its width and width is larger than its thickness.
- i.e. length>width>thickness.
- The flaky aggregates, Elongated aggregates Flaky & elongated aggregates are not suitable for concreting. It does not form a very good bond with concrete. These are generally obtained from poorly crushed rocks.
Classification depend on grading of aggregates
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
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