Things To Know By Site Civil Engineers

Concrete Grades

M7.5= 1 : 4 : 8
M10 = 1 : 3 : 6
M15 = 1 : 2 : 4
M20 = 1 : 1.5 : 3 (M20 & above grade based on Design Mix.

Example:-M15 concrete mix has a mix proportion of 1:2:4 of cement, fine aggregate, and coarse aggregate respectively. M15 – M represents Mix and 15 N/mm2 is the characteristic compressive strength of concrete cube at 28 days.

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.

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

DPC thickness minimum 25mm or 1 inch (for more details click this).

Weight of 1 cement bag is 50kg.

Riser of Staircase 150 to 200mm.

Tread of Staircase 250 to 300mm.

Staircase angle should 25 to 40degree.

Chair spacing maximum spacing is 1.00 m (or) 1 No per Square meter.

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.

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

Minimum thickness of slab is 125 mm.

Dimension tolerance for cubes + /– 2 mm.

Free fall of concrete is allowed maximum to 1.50m.

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 / mm2.

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

Electrical conduits shall not run in column.

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

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.

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

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

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

Cement shall be stored in dry places on a raised platform about 200mm above floor level and 300mm away from walls. Bags to be tacked not more than 10 bags high in such a manner that it is adequately protected from moisture and contamination.

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 result should be submitted to engineer for approval. If results are unsatisfactory necessary action/rectification/remedial measures has to be exercised.

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

Cement shall be tested for its setting.

The initial setting time shall not be less than 30 minutes.
The final setting time shall not be more than 10 hours.

Slump IS 456

Lightly reinforced 25 – 75 mm.
Heavily reinforced 75 – 100 mm.
Trench fill (insitu & Tremie) 100 – 150 mm (For Tremie no need of vibrator).

Curing Days Required

Super Sulphate cement : 7 days.
Ordinary Portland cement OPC : 10 days.
Minerals and Admixture added cement : 14 days

Test on Fresh concrete

Slump Test- Workability
Compacting Factor Test
Vee-Bee Test

Test on Hardened Concrete

Rebound Hammer Test
Ultrasonic Pulse Velocity Test

Field Tests of Cement

1.Date of Manufacturing: As the strength of cement reduces with age, the date of manufacturing of cement bags should be checked.

2.Cement Colour: The colour of cement should be uniform. It should be typical cement colour i.e. gray colour with a light greenish shade.

3.Whether Hard Lumps are Formed: Cement should be free from hard lumps. Such lumps are formed by the absorption of moisture from the atmosphere.

4.Temperature Inside Cement Bag: If the hand is plunged into a bag of cement, it should be cool inside the cement bag. If hydration reaction takes place inside the bag, it will become warm.

5.Smoothness Test: When cement is touched or rubbed in between fingers, it should give a smooth feeling. If it felt rough, it indicates adulteration with sand.

6.Water Sinking Test: If a small quantity of cement is thrown into the water, it should float some time before finally sinking.

7.The smell of Cement Paste: A thin paste of cement with water should feel sticky between the fingers. If the cement contains too much-pounded clay and silt as an adulterant, the paste will give an earthy smell.

8.Glass Plate Test: A thick paste of cement with water is made on a piece of a glass plate and it is kept under water for 24 hours. It should set and not crack.

9.Block Test: A 25mm × 25mm × 200mm (1”×1”×8”) block of cement with water is made. The block is then immersed under water for three days. After removing, it is supported 150mm apart and a weight of 15kg uniformly placed over it. If it shows no sign of failure the cement is good.

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