ALL YOU WANT TO KNOW ABOUT CONCRETE BLOCKS

 ALL YOU WANT TO KNOW ABOUT CONCRETE BLOCKS

CONCRETE BLOCKS

In areas where good quality bricks are not economically available, concrete blocks are used instead of bricks. The blocks can be solid, hollow or cavity depending on the requirements. blocks can be made for any desired dimension derived from the site or from a factory. There are small manual and motor engines to made the blocks. The blocks are to be made as per I.S.2185 (Pt.1&2)- 1979.

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THE BLOCKS ARE NORMALLY OF SIZES

SIZES AVAILABLE IN INCHES
24x8x8	16x8x8
24x8x6	16x8x6
24x8x4	16x8x4

SIZES AVAILABLE IN MILLIMETER (mm)
600x200x200	400x200x200
600x200x150	400x200x150
600x200x100	400x200x100

THE MINIMUM REQUIREMENTS OF CONCRETE BLOCKS ARE AS UNDER,

PROPERTY	MINIMUM REQUIREMENT
Compressive strength of concrete (Min.)	4.0 N/mm2 Achieved by 1:5:10 concrete.
The density of concrete (Max.)	1800 Kg/m3
water absorption (Max.)	10%

TYPES OF CEMENT BASED BLOCKS

1. SOLID CONCRETE BLOCK

Pros:

Compressive strength 5 – 8 Mpa, Highest among its substitutes; can be manufactured at the site for economical production (no transportation, taxes).Lowest water absorption among its class

Cons: 

High Density (2100 to 2200 kg/cum)dead load on the structure is high – reinforcement consumption increases, heavy to handle, Dimension variations are observed, chiselling for services (Electrical and Plumbing) installation is labour intensive and time-consuming.

Typical sizes available:

400x200x200mm, 400x200x150mm, 400x200x100mm

Used In

Low rise construction

2. HOLLOW CONCRETE BLOCK

Pros:

Compressive strength 5 – 8 Mpa, lightweight (density = 1250 to 1400) kg/cum, the dead load on structure reduces – reinforcement consumption optimised), can be manufactured at the site for economical production (no transportation, taxes).

Cons:

Services installation requires concrete filling post chiselling, Wastage in high.

Typical sizes available:

400x200x200mm, 400x200x150mm, 400x200x100mm

Used in:

Low rise construction

3. LIGHTWEIGHT AERATED CONCRETE BLOCK

Pros:

lightweight (density = 600 – 700 kg/cum),very light to handle, dead load on structure reduces – reinforcement consumption can be optimized, ease in chiselling for services (Electrical and Plumbing) installation is less labour intensive and low time consuming, dimension accuracy is high, better thermal and acoustic properties, plaster consumption is low.

Cons :

Compressive strength 3 – 5MPa, to be handled properly for low breakages, cannot be manufactured at the site, the Unit cost is high.

Typical sizes available:

600x200x200mm, 600x200x150mm, 600x200x100mm

Used in:

High rise construction

4. Cellular Lightweight Concrete Block

Pros:

lightweight (density = 550 to 650 kg/cum, dead load on structure reduces – reinforcement consumption-optimized), dimension accuracy is high, ease in chiselling for services (Electrical and Plumbing) installation is less labour-intensive and low time consuming, better thermal and acoustic properties can be manufactured at site for economical production (no transportation, taxes), plaster consumption low.

Cons:

Compressive strength 3 – 4MPa is low in comparison to other substitutes, Better quality control required for production to be handled properly for low breakages.

Typical sizes available:

600x200x200mm, 600x200x150mm, 600x200x100mm

Best Use

High rise construction

5. Fly Ash Blocks

Pros:

Compressive strength 3.5 – 5MPa, can be manufactured at site for economical production ease in chiselling for services (Electrical and Plumbing) installation is less labour-intensive and low time-consuming.

Cons:

High Density (2100 to 2200 kg/cum) Dimension variations observed, plaster consumption high

Typical sizes available:

600x200x200mm, 600x200x150mm, 600x200x100mm

400x200x200mm, 400x200x150mm, 400x200x100mm

Best Use:

low and mid-rise construction.

The concrete blocks suffer from one shortcoming that they shrink on drying and cause cracks in masonry. It is therefore essential that after curing the blocks for 28 days, they should be dried in the open air for at least 28 days before use to allow for initial shrinkage. Further maximum possible time is allowed before plastering the surface made with concrete blocks. Precautions are required in stacking for the blocks to allow maximum exposure for drying as below,

1.  Stacking area should be preferably in shade.

2.  The blocks should be stacked in rows and heaps with a gap of 50 mm between each, allowing for proper ventilation.

3.  There should be a gap of about 1 m after every 25 rows.

4. More than 6 blocks should not be stacked, one above other especially when they are green.

MUST-READ: Why use block masonry for your home construction?

QUALITY TESTS FOR CONCRETE BLOCKS

All tests recommended for bricks apply to the block. Similarly, the sample size is equal to that of bricks. The following field tests should be performed,

1.   Check the dimensions as per explained.

2.   The edges should be sharp, straight and at right angles.

3.   free from cracks

4.   It should not break when dropped down from 1.0 m height on hard ground

5.   Percentage of broken blocks should not be more than 5% in one truckload.

6.   Check the average weight of block and density should not be less   than 1800 Kg/m3]

7.   Water absorption, when kept in water for 24 hours, should not be more than 10% by weight of the block.

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