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The concrete Masonry Units or CMU are also called hollow blocks, concrete bricks, or concrete masonry.
Hallow concrete blocks are prepared of Portland cement and aggregate, the high-density blocks may utilize sand and gravel while low-density blocks utilize industrial waste in place of aggregate.
Lightweight hollow blocks are prepared by utilizing aerated concrete. The hollow concrete blocks are prepared, hardened, and cured before transporting to the site and are a very long-lasting and strong product.
1. Solid Concrete Blocks
Solid concrete blocks are commonly used, which are heavy in weight and manufactured from dense aggregate. They are very strong and provide good stability to the structures. So for large work of masonry like load-bearing walls, these solid blocks are preferable.
They are available in large sizes compared to bricks. So, it takes less time to construct concrete masonry than brick masonry.
2. Classification of Concrete Blocks
The hollow concrete blocks can be categorized into the following four types:
1. Grade ‘A’
These are utilized as load-bearing units and can contain the lowest block density of 1500 kg/m3. The hollow concrete blocks can be prepared for the lowest compressive strengths of 3.5, 4.5, 5.5, and 7.0 N/mm2 respectively, for 28 days.
2. Grade ‘B’
These are also utilized as load-bearing units and can contain a block density of 1500 kg/m3 but not less than 1000 kg/m3. These can be prepared for the lowest compressive strengths of 2.0, 3.0, and 5.0 N/mm2 respectively, for 28 days.
3. Grade ‘C’
These grades of concrete blocks are utilized as non-load-bearing units and can contain a block density of less than 1500 kg/m3 but not less than 1000 kg/m3. These shall be prepared for the lowest average compressive strength of 1.5 N/mm2 at 28 days.
4. Grade ‘D’
Solid concrete blocks can contain a block density of a minimum of 1800 kg/m3. These can be prepared for the lowest compressive strengths of 4.0 and 5.0 N/mm2, respectively.
3. Standard sizes of Hollow Block
39 cm x 19 cm 30 cm is the standard size of hollow concrete blocks.
39 cm x 19 cm x 20 cm and 39 cm x 19 cm x 10 cm is the standard size of hollow building tiles. The Absorption of water will be less than 10% in hollow solid block blocks for partitioning.
4. Properties of Hollow Block
The properties of hollow blocks are mentioned below:
1. Moisture Movement: Not more than 0.09%
2. Water Absorption: Not more than 10%
3. Drying Shrinkage: Not more than 0.06%
4. Compressive Strength:
For Grade A: 3.5 to 15.0 N/mm2
For Grade B: 3.5 and 5.0 N/mm2
5. Density:
For Grade A: 1500 kg/m3
For Grade B: 1100 kg/m3 to 1500 kg/m3
5. Uses of Hollow Block
Hollow concrete blocks are utilized in all types of masonry construction such as
✔ It is used in exterior load-bearing walls
✔ It is used in interior load-bearing walls
✔ It is also used in curtain walls
✔ It is used in partition walls and panel walls
✔ Backing from brick, stone, and other facing
✔ Fireproofing over a structural member
✔ Fire-safe walls around stairwells, elevators
✔ Piers, column and retaining walls, etc.
✔ Boundary fences
6. Advantages of Hollow Blocks
The advantages of Hollow blocks are as follows:
✔ These blocks are more cost-effective than other traditional wall systems or wall construction systems.
✔ Solid hollow blocks need less maintenance and give insulation from sound, and heat, and are fire-resistant.
✔ The joints in these blocks need less cement mortar, and little or no plastering thus speeding up the construction process and also saving cost.
✔ It provides high dimensional accuracy and a consistent finish making it an ideal building material for building load-bearing structures and building partition walls.
✔ These hollow concrete blocks have high-stress bearing capacity hence widely used in building construction practices.
✔ The hollow blocks are lightweight and hence utilized in the construction of homes in earthquake-prone areas.
✔ The hollow block will provide a various look as it decreases the energy bill to produce an environmentally friendly environment in the building.
✔ Hollowing space in blocks prepares masonry work soundproof, heatproof, and damp proofing.
✔ It is fully energy-efficient and does not need any non-renewable resources for its manufacture.
✔ Also, it does not disturb the ecosystem so they are either environmentally friendly or eco-friendly since the waste and local resources can be used for their manufacture or production.
✔ It can also be prepared at the site.
✔ It is of high quality, high strength, uniform size, and shape.
7. Disadvantages of Hollow Blocks
The disadvantages of Hollow blocks are as follows:
✔ Maintenance cost is high.
✔ Concrete blocks have a low bearing capacity as the average mass of wall decoration materials is reduced, and the load-bearing capacity is usually decreased.
✔ It is very risky to hang huge things on walls.
✔ Hollow blocks are porous so, a high chance of water seepage.
8. Cost of Hollow Blocks
The cost of hollow blocks varies from one country to another. The rate of blocks can get high if the rate of cement, sand, and aggregates gets high.
Here is the average cost of concert blocks in different countries:
✔ In India, the cost of hollow blocks is around Rs 28/Piece.
✔ In Nepal, the cost of hollow blocks is around Rs 86 for a 4-inch wide.
✔ In the USA, the cost of hollow blocks is around 1$ to 3 $ per block.
✔ In the Philippines, the cost of hollow blocks is around ₱15.00 – ₱23.00.
✔ In Canada, the cost of hollow blocks is around CA ( $1.93 to $3.29 ).
9. Difference Between Hollow Blocks and Solid Concrete Blocks
| S.No | Solid Concrete Blocks | Hollow Blocks |
| 1. | Solid in Nature. | Hollow in Nature. |
| 2. | More in weight. | Less in weight. |
| 3. | The conductivity of heat is high (less thermal insulation) | The conductivity of heat is low (more thermal insulation) |
| 4. | It doesn’t provide a facility to conceal, conduits, etc. | It provides a facility to conceal, conduits, etc. |
| 5. | Lean mixes are used. | Needs a richer mix. |
| 6. | No fine concrete is used. | Fine aggregate is more (as high as 60%) |
10. QNA
1. How much concrete to fill hollow blocks?
⇒ To fill 150 mm ‘H’ blocks permits 0.65 m3 of concrete per 100 blocks. Filling 200mm blocks permits 0.8 m3 of concrete per 100 blocks.
To fill, 200mm ‘H’ blocks permit 0.84 m3 of concrete per 100 blocks.
2. How many hollow blocks are in 1 square meter?
⇒ The total number of 10 blocks is 1 m2.
3. How much is a hollow block in the Philippines?
⇒ Note: All prices are in Php.
| Concrete Hollow Block Wall Masonry Work | ||
| Concrete Hollow Blocks (CHB) 4″ | pc | 12.00 |
| Concrete Hollow Blocks (CHB) 6″ | pc | 18.00 |
| Portland Cement, 40 kg. | bag | 261.00 |
| Washed sand | m3 | 1,365.00 |
| 10 mm. Dia. x 6.0 M. DSB | pc. | 159.00 |
| Tie Wire #16 | kg. | 61.00 |
| Stone Masonry Works | ||
| Cement | bag | 262.00 |
| Sand | m3 | 1,432.00 |
| Gravel Fill | m3 | 1,417.00 |
| Weep Holes (PVC) | Lm. | 201.00 |
| Filter Cloth | m2 | 260.00 |
| Boulders | m3 | 1,482.05 |
| Screened Sand | m3 | 1,550.00 |
| Screened Gravel | m3 | 1,590.00 |
4. How to make hollow blocks?
⇒ The process of preparing hollow blocks is as follows:
✔ The ratio of 1:2:3 is prepared of the cement, sand, and gravel in the mold flows water until the mixture of concrete is good sufficient to flow into the container (mold).
✔ Blend the water into the mold.
✔ Use a steel rod to stir the mixture regularly.
✔ Now, leave the block to dry for 1-2 days, as a result, hardened hollow blocks are prepared to be used in construction work.
5. How to anchor into a hollow cinder block?
⇒ When drilling into a cinder block to keep a concrete anchor, a hammer drill should be utilized with a drill bit that has a carbide tip.
Drilling into the solid section does not make or raise any problems when utilizing a masonry bit. The hammer drill will make the hole effortlessly into the cinder block.
| Read Also: Block Wall Calculation |
