Construction blogs

Lets Achieve Success Together

common mistakes on construction site

Common mistakes on construction site

Every civil engineer or civil supervisor should be aware of these Common mistakes happening on construction site related to concreting, reinforcement, shuttering, steel and cover are :

Concreting :

1. Poor quality placing

According to IS: 456-2000 concrete shall not be freely dropped into place from a height exceeding 1.5 meters .

No concrete shall be allowed without vibration (vibrator) except under water concreting or tremie concreting .

2. Poor quality concrete

Concrete shall be placed within 90 min (when the atmospheric temperature is above 20 degree celsius ) and within 120 min (when the atmospheric pressure is at or below 20 degree celsius .

Strictly avoid addition of extra water at batching plant or at site .

When concrete is conveyed by chute, than the slope of chute shall be so adjusted that the concrete flows without bleeding of concrete and segregation of its ingredients. Concrete Mix without proper slump or without proper cohession shall not be used .

Reinforcment :

1. The reinforcement bars, ties, links, stirrups and all other reinforcement shall be positioned and rigidly fixed in the position shown in the drawing ..

2. Bars shall not be bent or straightened in a manner that will damage the parent material . bars shall not be heated to facilitate straightening.

3. Lap splices are considered to be staggered if the center to center distance splices is not less then 1.3 times the lap length .

4. Reinforcement bars shall be adequately secured by chairs / ties / hanger, So that it will maintain its position during casting and vibrating the concrete .

5. Reinforcement shall be free from rust, mortar, loose material, greese or oil .

Clear cover to Reinforcement :

1. Clear cover shall not be less than the size of the bar or the maximum aggregate size plus 5mm. In case of the bundle bars, it should be equal to or greater than the size of single bar of equivalent area plus 5mm .

2. From durability consideration , minimum cover shall be :

Type of structure Clear Cover (in mm ) for environmental condition 
Extreme Severe Moderate
Slab  50 35 25
Beam /Girder 60 50 35
Column  75 75 50
Well, Pile & Footing  75 75 50

Form work :

1. Formwork shall be so constructed and supported as to remain sufficiently rigid during placement and compaction of the concrete .

2. Formwork shall be sufficiently water tight to prevent loss of water or mortar from concrete .

3. The numbers of joints in the formwork shall be kept minimum for smooth surface.

Minimum period before removal of formwork

Member Minimum time for removal of formwork
Wall, columns and vertical faces of all structural members 24 to 48 hours
Slabs (props left under )* 3 days
Beam sofit (props left under )* 7 days
Removal of props under slab
1. Spanning upto 4.5 m
2. Spanning over 4.5m

7 days
14 days
Removal of props under Beams
1. Spanning upto 6m
2. Spanning over 6m

14 days
21 days

Curing:

1. In Moist curing the concrete should be kept constantly wet for a minimum period of 14 days. Water should be applied on unformed surfaces immediately after the forms s are stripped. The concrete shall be kept constantly wet by ponding or covered with the layer of sacking, Canvas, Hessian or a similar absorbant material. While concrete sets, It gains strength as the process of hydration slowly spreads the entire body of structure.

2. In curing compound, The compound shall be applied to all exposed surfaces of the concrete along with stripping of form-work.Curing compound shall not be used on any surface requiring further finishing to be applied.