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Selection of Building Materials
Some Suggestions
A) Sand:
- Should be free from – Clay, Dirt, Mica & Shales etc.
B) Brick:
- Shape should be proper.
- Corners should be sharp, not broken.
- Color should be uniform.
- Ringing sound in collision.
- Water absorption not more than 15%, etc.
C) Steel Reinforcement:
- Free from – rust, cracks, piping, oils, grease.
- Strength in proportion with concrete.
D) Aggregate:
- Should be solid, cubical and free from dirt.
- Do not contain clay, mud or dirt particles.
- Should be graded (small to large), not single size.
E) Water:
- Drinkable water is best one.
- Waste water from industries may be harmful.
- Should be free from clay, oil and grease.
- Maximum water decrease strength & durability.
F) Cement:
- Only high grade of cement can not increase the strength of concrete.
- Grade of cement should be just higher the grade of concrete.
- Higher grade of cement produces more heat of hydration and cracks.
- Quantity of cement can not increase strength, water-cement ratio should be decreased.
- Quantity of cement can not be saved using higher grade, while water-cement ratio not decreased. But it can not be done without admixture for required workability.
Note:
- You can replace switch, bulb, finishing, but not the structure (cement, sand & aggregate). The cost of structure is only 30-40% of total cost.
- For the good quality of construction you have to pay only 10-12% more cost than you think.
- After addition of water, concrete and/or mortar should be placed at position within 3 hrs, not whole day.
- More water cannot give the best compaction, but giver porous & weak concrete.
Grade of Cement:
Grade of cement only indicates the compressive strength of cement (not concrete) at 28 days. But cements continues to increase the strength beyond 28 days, with not much difference in long-term strength.
Required Compressive strength of Various Grades of Ordinary Portland Cement (OPC)
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Minimun compressive strength(N/mm2 |
| Age |
33 Grade |
43 Grade |
53 Grade |
| 3-days. |
16.0 |
23.0 |
27.0 |
| 7-days. |
22.0 |
33.0 |
37.0 |
| 28-days. |
33.0 |
43.0 |
53.0 |
Other Cements
Portland pozzolana cement
Similar to OPC, but increases impermeability, lower heat of hydration, reduces alkali-aggregate reaction and improve resistance to aggressive chemicals.
Portland blast furnace slag cement (Portland slag cement)
Similar to OPC, but lower heat of hydration, better resistance to chemical attack.
Quick setting cement
Cement having the higher strength at early age is not a sign of higher strength at 28 days, but is the sign of higher heat of hydration.
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Cost of condtruction |
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Estimating the cost of construction |
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