Coarse Aggregate
Coarse Aggregate consists of natural occurring stones (crushed, uncrushed or broken). It should be hard, strong, dense, durable, and clean. It must be free from veins, adherent coatings and injurious amounts of disintegrated pieces, alkali, vegetable matter and other deleterious substances. It should be roughly cubical in shape. Flaky pieces should be avoided. It should confirm to IS: 2383(I).
Grading of coarse aggregate
Coarse Aggregate should be either graded or single sized as specified in the table given below.
Characteristics of coarse aggregate
1. The coarse aggregate is clean, hard, non porous, free from lumps of clay and vegetable matter.
2. Water absorption of aggregate is not more than 10 % of its weight after 24 hours immersion in water.
3. Angular and roughly cubicle particles are ideal. River gravels make the best coarse aggregate.
4. Aggregate is chemically inert material.
5. Brick aggregate is not used in RCC work.
S. No. |
IS Sieve size of Designation(mm) |
Percentage
40mm |
passing
20mm |
(by weight)
16mm |
for nominal
12.5mm |
1. |
75 |
100 |
---- |
---- |
---- |
2. |
37.5 |
95-100 |
100 |
---- |
---- |
3. |
19 |
33 - 70 |
95-100 |
100 |
---- |
4. |
16 |
---- |
---- |
95 - 100 |
100 |
5. |
11.2 |
---- |
---- |
---- |
90 -100 |
6. |
9.5 |
10 - 35 |
25 -35 |
30 - 70 |
40 -85 |
7. |
4.75 |
0-5 |
0-10 |
0-10 |
0 - 10 |
Deleterious substances in coarse aggregate
Coarse Aggregate should not contain any of the following deleterious materials.
- Pyrites
- Coal
- Lignite
- Mica
- Clay
- Alkali
- Soft fragments
- Sea shells
- Shale or similar laminated material
NOTE: The maximum quantity of deleterious materials should not be more than 5% of the weight of the aggregate when determined in accordance with IS: 2386(I).
Precautions while using coarse aggregate
The following precautions should be taken while using coarse aggregate in RCC (Reinforced Cement Concrete) Work.
1. Aggregate should be stacked on a hard, dry and level patch of ground.
2. Coarse aggregate should not contain any material liable to attack steel reinforcement.
3. Aggregate which are chemically reactive with alkalies of cement should not be used.
4. Proper graded material should be used for achieving good bond stress.
5. Aggregate should be washed with clean water before the use.
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Fine sand should consist of natural sand or crushed stone sand. It should be hard, durable, clean and be free from organic matter etc. and should not contain any appreciable amount of clay balls and harmful impurities such as alkalis, salts, coal, decayed vegetation etc.
Cracks can happen due to foundation movements and settlements of building, thermal movements, chemical reactions, elastic deformations and shrinkage etc. in buildings. They can damage plaster of walls, ceilings and destroy the beauty of the structure also. Let’s know their reasons in detail and get preventive measures.