Civil Engineering Important Points to Remember

1.      Minimum thickness of slab is 125 mm.

2.      Water absorption should not be more than 15 %.

3.      Dimension tolerance for cubes + – 2 mm.

4.      Lapping is not allowed for the bars having diameters more than 36 mm.

5.      Chair spacing maximum spacing is 1.00 m (or) 1 No per 1m².

6.      For dowels rod minimum of 12 mm diameter should be used.

7.      Chairs minimum of 12 mm diameter bars to be used.

8.      Longitudinal reinforcement not less than 0.8% and more than 6% of gross C/S.

9.      Minimum bars for square column is 4 No’s and 6 No’s for circular column.

10.  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.

11.  Minimum thickness of slab is 125 mm.

12.  Dimension tolerance for cubes + 2 mm.

13.  Free fall of concrete is allowed maximum to 1.50m.

14.  Lap slices not be used for bar larger than 36 mm.

15.  Water absorption of bricks should not be more than 15 %.

16.  PH value of the water should not be less than 6.

17.  Compressive strength of Bricks is 3.5 N / mm

18.  In steel reinforcement binding wire required is 8 kg per MT.

19.  In soil filling as per IS code, 3 samples should be taken for core cutting test for every 100m².

20.  Compressive strength of Bricks is 3.5 N /mm².

21.  Maximum Free fall of concrete allowed is 1.50 m.

22.  In soil filling as per IS code for every 100 sqm 3 sample for core cutting test should be taken.

23.  Electrical conduits shall not run in column.

24.  Earth work excavation for basement above 3 m should be stepped form.

25.  Any back filling shall be compacted 95% of dry density at the optimum moisture content and in layers not more than 200mm for filling above structure and 300 mm for no structure.

26.  F soling is specified the soling stones shall be laid at 45° to 60° inclination (and not vertical) with interstices filled with sand.

27.  A set of cube tests shall be carried out for each 30 cum of concrete / each levels of casting / each batch of cement.

28.  Water cement ratio for different grades of concrete shall not exceed 0.45 for M20 and above and 0.50 For M10 / M15.

29.  For concrete grades M20 and above approved admixture shall be used as per mix design requirements.

30.  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.

31.  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.

32.  Water used for both mixing and curing shall be clean and free from injurious amounts of oils, acids, alkalis, 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.

33.   

Calculating Cement, Fine Aggregate & Coarse Aggregate for Mortar Mixes

For example, consider 1:4 mortar, 1 cum of cement mortar work is to be done

1:4 means 1 part of Cement by volume 4 parts of fine aggregate by volume

Total volume = 1 cum

Quantity of Cement = (1/ (1+4)) x 1 = 0.20 cum
1 cum of Cement = 1441 Kg
Cement quantity required = 1441 x 0.20 = 288.2 Kg

Quantity of Sand = (1/ (1+4)) x 4 = 0.80 cum

We have not done it correct; the above quantity would yield hardly 0.63 cum of mortar because we have not considered voids & cavities. So, we have to increase quantity by 50 – 60%.

So, the final quantity for producing 1 cum 1:4 mortar is

Cement = 288.2 + 60 % (for voids & cavities) = 288.2 x 1.6 = 461.12 Kg

Sand = 0.80 + 60 % (for voids & cavities) = 0.80 x 1.6 = 1.28 cum

Following are few general points to remember for civil site engineers to make the construction work easier while maintaining quality of construction.

·         Lapping is not allowed for the bars having diameters more than 36 mm.

·         Chair spacing maximum spacing is 1.00 m (or) 1 No per 1m².

·         For dowels rod minimum of 12 mm diameter should be used.

·         Chairs minimum of 12 mm diameter bars to be used.

·         Longitudinal reinforcement not less than 0.8% and more than 6% of gross C/S.

·         Minimum bars for square column is 4 No’s and 6 No’s for circular column.

·         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.

·         Minimum thickness of slab is 125 mm.

·         Dimension tolerance for cubes + 2 mm.

·         Free fall of concrete is allowed maximum to 1.50m.

·         Lap slices not be used for bar larger than 36 mm.

·         Water absorption of bricks should not be more than 15 %.

·         PH value of the water should not be less than 6.

·         Compressive strength of Bricks is 3.5 N / mm^2.

·         In steel reinforcement binding wire required is 8 kg per MT.

·         In soil filling as per IS code, 3 samples should be taken for core cutting test for every 100m².

Density of Materials:

Material	Density
Bricks	1600 – 1920 kg/m3
Concrete block	1920 kg/ m3
Reinforced concrete	2310 – 2700 kg/ m3

 

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

De-Shuttering time of different RCC Members

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

Cube samples required for different quantity of concrete:

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

leases and load transfers that are worked out during the design stage will not be achieved and this poses a serious liability on the structural stability. It is important for us to remember that calculations worked out on a piece of paper will mean nothing if we are not able to co-relate them with practical conditions.