BASIC IMPORTANT POINTS OF CONSTRUCTION KNOWLEDGE TO REMEMBER
This important points in construction may help the new engineers and Site supervisors in fulfilling their duties as site supervisors.
1.Minimum diameter of bars used in slab = 8mm.
2. Minimum diameter of bars used in column = 12mm.
3. Minimum number of bars used in square or rectangular column = 4 bars.
4. In Cantilever Beam Tension Zone is Up & compression zone is Below where as in simply supported Beam Compression Zone is above & Tension is Below
5.Lapping is not allowed for the bars having diameters more than 36 mm.
6. Chair spacing maximum spacing is 1.00 m (or) 1 No per 1m2.
7. For dowels rod minimum of 12 mm diameter should be used.
8. Chairs minimum of 12 mm diameter bars to be used.
9. Longitudinal reinforcement not less than 0.8% and more than 6% of gross C/S.
10. Minimum bars for square column is 4 No’s and 6 No’s for circular column.
11. Main bars in the slabs shall not be less than 8 mm (HYSD) or 10 mm (Plain bars) and the distributors not less than 8 mm and not more than 1/8 of slab thickness.
12. Minimum thickness of slab is 125 mm.
13. Dimension tolerance for cubes + 2 mm.
14. Density of Construction Material
| Material | Density |
| Bricks | 1600 – 1920 kg/m3 |
| Concrete block | 1920 kg/ m3 |
| Reinforced concrete | 2310 – 2700 kg/ m3 |
15. Maximum diameter of bars used in slab = 1/8 × thickness of slab.
16. Free fall of concrete is allowed maximum to 1.50m.
17. Water absorption of bricks should not be more than 15 %.
18. PH value of the water should not be less than 6.
19. Compressive strength of Bricks is 3.5 N / mm2.
20. In steel reinforcement binding wire required is 8 kg per MT.
21. In soil filling as per IS code, 3 samples should be taken for core cutting test for every 100m2.
22. Samples from fresh concrete shall be taken and at least a set of 6 cubes of 150mm shall be prepared and cured. 3 Cubes each at 7 days and 28 days shall be tested for compressive strength. The test results should be submitted to engineer for approval. If results are unsatisfactory necessary action/rectification/remedial measures has to be exercised.
23. Water used for both mixing and curing shall be clean and free from injurious amounts of oils, acids, alkali, salts, sugar and organic materials or other substances that may be deleterious to concrete or steel. The PH. shall be generally between 6 and 8.
24. Lap length for M20 concrete:
Columns – 45d
Beams – 60d
Slabs – 60d
25. Standard size of brick = 190mm×90mm×90 mm = 19cm×9cm×9cm.
26. A good brick clay contains 20 to 30% of alumina, 50 to 60% of silica and the remaining constituents are Lime, Magnesia, Sodium, Potassium, Manganese and iron oxide.
27. Color of good brick is deep red, cherry or copper colored.
28. Compressive strength of bricks is 3.5 N/mm2.
29. Ordinary Portland cement consists of 62 to 67% of Lime.
30. The initial setting time of ordinary portland cement should not be less than 30 minutes.
31. The final setting time of ordinary portland cement should not be more than 10 hours.
32. Initial and Final setting time of cement is determined by Vicat’s apparatus.
46. The normal consistency of portland cement is about 25%.
47. When concrete is to be laid under water, Quick setting cement is used.
48. Maximum free fall of concrete allowed to 1.50m.
49. Curing time of RCC Members for different types of cement
Super Sulphate cement: 7 days Ordinary Portland cement
OPC: 10 days
Minerals & Admixture added cement: 14 days
50. Deshuttering Period of RCC member
| RCC Member | De-shuttering time |
| For columns, walls, vertical form works | 16-24 hrs. |
| Soffit formwork to slabs | 3 days (props to be refixed after removal) |
| Soffit to beams props | 7 days (props to refixed after removal) |
| Beams spanning upto 4.5m | 7 days |
| Beams spanning over 4.5m | 14 days |
| Arches spanning up to 6m | 14 days |
| Arches spanning over 6m | 21 days |
51. Test On Fresh Concrete
(a). Slump Test – Workability. (b). Compacting Factor. (c). Vee-Bee Test.
52. Test On Hardened Concrete
(a). Rebound (Schmidt) Hammer Test. (b). Ultrasonic Pulse Velocity Test.
53. The excess of silica in the clay makes the brick brittle and weak.
54. Process of manufacturing of bricks consists of Preparation of brick clay, Moulding bricks, Drying of bricks and Burning of bricks.
55. Moulding of bricks may be hand moulding or machine moulding.
56 .The burning of dry bricks is done either in clamp or in a kiln.
57. The ingredients of ordinary cements are Lime, Silica, Alumina, Calcium sulphate, Iron oxide, Magnesia, Sulphur & Alkali’s.
58. Ordinary Portland cement consists of 62 to 67% of Lime.
59.Slump Range of concrete
| Concrete Mixes | Slump range in mm |
| Columns, Retaining walls | 75-150 mm |
| Beams & Slabs | 50-100 mm |
| CC Pavements | 20-30 mm |
| Decks of bridge | 30-75 mm |
| Vibrated Concrete | 12-25 mm |
| Huge Mass constructions | 25-50 mm |
60. Electrical conduits shall not run in column.
61. Earth work excavation for basement above 3 m should be stepped form.
62. Any back filling shall be compacted 95% of dry density at the optimum moisture content and in layers not more than 200 mm for filling above structure and 300 mm for no structure.
63. soling is specified the soling stones shall be laid at 45° to 60° inclination (and not vertical) with interstices filled with sand.
64. A set of cube tests shall be carried out for each 30 cum of concrete / each levels of casting / each batch of cement.
65. Water cement ratio for different grades of concrete shall not exceed 0.45 for M20 and above and 0.50 For M10 / M15.
66. For concrete grades M20 and above approved admixture shall be used as per mix design requirements.
67.Cement shall be stored in dry places on a raised platform about 200mm above floor level and 300mm away from walls. Bags to be stacked not more than 10 bags high in such a manner that it is adequately protected from moisture and contamination.
68. Cube Quantity
| Quantity of Concrete | No. of cubes required |
| 1 – 5 m3 | 1 No’s |
| 6 0 15 m3 | 2 No’s |
| 16 – 30 m3 | 3 No’s |
| 31 – 50 m3 | 4 No’s |
| Above 50 m3 | 4 + 1 No’s of addition of each 50 m3 |
69. Height of window = 2.1m.
70. Minimum thickness of lintel = 15cm
71. 1 bag of cement = 1.25 cubit feet = 0.0347 cubic meter.
72. No. of cement bags in 1m^3 = 28.8 bags.
