Now, let us discuss some of the common questions regarding concrete cover blocks or spacer blocks.
 |
| Concrete cover block |
1. What are Concrete cover blocks?
The precast concrete product, which is used to provide the necessary covers or spacing for the reinforcement bars from the formwork, in all the RCC structures like slab, column, beam, footing, etc. are called concrete cover blocks or concrete spacer blocks. They are available in a variety of shapes and sizes as per their specific use.2. What is the necessity of concrete cover blocks?
All the rebars in the concrete structures need concrete covers due to the following reasons.
1. The rebars get corroded when exposed to the external environment which results in premature failure of the structure. To avoid such a situation, rebars should be embedded in the concrete with proper covers.
2. RCC structures need concrete cover to the rebar so that the stresses are transferred to the rebar from the surrounding concrete with proper bonding and hence it provides safety from slipping away.
3. Thermal insulation and fire protection for the rebars fits in a priority list for all the RCC structures. Providing the proper concrete cover to the rebars helps in achieving this condition.
Concrete cover blocks/spacer blocks when provided to the rebars at the proper spacing, it helps in achieving all the criteria mentioned above.
3. What is the proper cover for the rebars?
Concrete covers for the rebars normally range from 15mm to 50 mm in the general RCC structures. But in the heavier infrastructures and in the harsh environmental conditions it may go up to 100mm and sometimes even more.
The following are the typical covers provided for the common RCC structures in the Indian context. in normal conditions.
| Sl.no. | RCC structures | Cover in mm. |
| 1. | Slab | 20mm. |
| 2. | Beam | 25mm. |
| 3. | Column | 40mm |
| 4. | Footing | 50mm. |
4. What should be the spacing distance of the concrete cover blocks?
The distance between the two cover blocks depends upon the diameter of the rebar, the type of RCC structure, and rebar directions (longitudinal or transverse). When the rebar diameter increases there will be less sagging and hence the number of cover blocks requirement becomes less as the bar dia. increases.
Given below are the average distance between the cover blocks in different RCC members in normal conditions.
Sl. No.
|
RCC structures
|
Rebar diameter
|
Spacing/ distance
|
1.
|
Slab
|
6mm
8mm
Over 10mm
|
50cm.
60cm.
70cm.
|
2.
|
Column
a. Longitudinal
direction.
|
Up to 10mm.
12mm - 20mm.
Above 20mm.
|
50cm.
60-90cm.
100cm.
|
3.
|
Beam
a. Longitudinal
direction.
|
Up to 10mm.
12mm - 20mm.
Above 20mm.
|
30cm.
40cm - 70cm.
80cm.
|
4.
|
Footing
|
Similar to slab
| Appr. similar to the slab
.
|
Sl. no.
|
RCC structures
|
Width/height in mm.
|
No. of cover blocks.
|
1.
|
Column
b. Transverse
direction.
|
Up to 100mm.
Above 100mm
|
2 nos.
3 nos.& above
|
2.
|
Beam
b. Transverse
direction.
|
Up to 100mm.
Above 100mm.
|
2nos.
3nos &
above.
|
5. What is the quantity of cover block/spacer block for the RCC slab?
Given below are the average number of concrete cover blocks required for the RCC slab of area 100 sq m. and 1000 sq ft. respectively.
Sl.No.
|
RCC Structures
|
Rebar diameter
|
No. of cover blocks for 100 sq m.
|
No. of cover blocks for 1000 sq ft.
|
1.
|
Slab
|
6mm.
|
400 nos.
|
370 nos.
|
2.
|
Slab
|
8mm.
|
280 nos.
|
255 nos.
|
3.
|
Slab
|
10mm & above
|
210 nos.
|
190 nos.
|
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