Hollow bricks, also known as hollow concrete blocks or hollow concrete masonry units (CMUs), are commonly used in construction as a replacement for traditional bricks.
They are made from cement, water, and aggregates such as sand, gravel, or crushed stone, and feature hollow spaces that run through the center of the block.
Grades of hollow bricks
ASTM C652 defines two grades of these types of bricks based on their resistance to frost and weathering, as well as their exposure to water and freezing temperatures.
These two grades are
Grade SW:
This type of hollow brick is intended for use in areas where a high and uniform degree of resistance to frost action and disintegration by weathering is required.
It is suitable for applications where the hollow brick may be frozen when permeated with water.
Features of Grade SW Hollow Blocks:
- High and uniform resistance to frost action and weathering
- Ideal for areas with high exposure to water and freezing temperatures
- Provides excellent durability and long-lasting performance
Grade MW:
This type of hollow brick is intended for use in areas where a moderate and somewhat non-uniform degree of resistance to frost action is permissible.
It is also suitable for areas where the hollow brick is unlikely to be permeated with water when exposed to temperatures below freezing.
Features of Grade MW Hollow Blocks:
- Moderate and somewhat non-uniform resistance to frost action
- Suitable for areas with low exposure to water and freezing temperatures
- Provides reasonable durability and performance
Types of hollow bricks
ASTM C652 defines four types of hollow bricks based on their intended use and desired characteristics, including precision, texture, color, and appearance.
These four types are
Type HBS:
This type of hollow brick is designed for general use in masonry applications. It is suitable for a wide range of construction projects and offers a standard level of quality and performance.
Features of Type HBS Hollow Blocks:
- General use in masonry
- The standard level of quality and performance
Type HBX:
This type of hollow brick is also designed for general use in masonry but offers a higher degree of precision and lower permissible variation in size than Type HBS.
Features of Type HBX Hollow Blocks:
- General use in masonry
Type HBA:
This type of hollow brick is selected for use in masonry to produce characteristic architectural effects resulting from non-uniformity in the size and texture of the individual units.
It is designed to add a unique and distinctive aesthetic to a building’s appearance.
Features of Type HBA Hollow Blocks:
- Selected to produce characteristic architectural effects
Type HBB:
This type of hollow brick is designed for general use in masonry where a particular color, texture, finish, uniformity, or limits on cracks, warpage, or other imperfections detracting from the appearance are not a consideration.
Features of Type HBB Hollow Blocks:
- General use in masonry
Properties of hollow bricks
1. Compressive Strength
The compressive strength of these bricks is around 3.5 N/mm2, which is lower than that of solid bricks. However, it is still strong enough to support the weight of the building.
2. Dry Density
The dry density of hollow bricks is in the range of 694-788 kg/m3, which is lower than that of solid bricks. This makes them lighter and easier to handle during construction.
3. Water Absorption
The water absorption of hollow bricks is about 8% of the total weight of a brick. This means that they are less prone to absorbing moisture and becoming weakened over time.
4. Thermal insulation
These bricks provide good thermal insulation due to the presence of air cavities within the unit. This helps in reducing heat transfer and maintaining a comfortable indoor temperature.
5. Fire resistance
These bricks have excellent fire resistance properties, which makes them suitable for use in fire-rated walls and buildings.
6. Sound insulation
These bricks can absorb sound and provide good sound insulation, which makes them useful in reducing noise levels in buildings.
7. Durability
These bricks are strong and durable and can withstand heavy loads and adverse weather conditions. They are also resistant to moisture, pests, and mold.
8. Lightweight
These bricks are lightweight compared to solid bricks, which makes them easier to handle and install.
9. Cost-effective
These bricks are cost-effective as they require fewer materials, have a shorter construction time, and are energy-efficient.
Sizes hollow bricks
These bricks are available in various sizes and shapes and can be used for a variety of applications such as load-bearing walls, partition walls, retaining walls, and foundations.
They are also available in different densities, which can affect their strength and insulation properties. Here is the list of different sizes of hollow bricks along with their uses.
| S. No | Size in mm | Use |
| 1 | 400 x 200 x 200 | This is a larger size of hollow brick that is commonly used for the construction of load-bearing walls and other structural elements. |
| 2 | 400 x 150 x 250 | This is another larger size of a hollow brick that is sometimes used for the construction of load-bearing walls and other structural elements. |
| 3 | 400 x 100 x 200 | This is a smaller size of a hollow brick that may be used for non-load-bearing walls or partitions. |
| 4 | 400 x 200 x 300 | This is a larger size of a hollow brick that is sometimes used for the construction of load-bearing walls and other structural elements, particularly in regions with seismic activity. |
Price of hollow bricks
In the United States, the price of hollow bricks can range from around $0.50 to $3 per piece, depending on the size, quality, and manufacturer.
In India, the price of hollow bricks can range from around Rs 20 to Rs 50 per piece, depending on the size, quality, and location.
In England, the price of these bricks can range from around £0.80 to £3 per piece, depending on the size, quality, and manufacturer.
Benefits of hollow bricks
- Lightweight and easy to handle, reducing transportation and construction costs.
- Better insulation properties due to the air pockets inside the bricks.
- Faster construction times due to larger brick sizes and ease of handling.
- Lower water absorption rates, reducing the risk of mold growth and efflorescence.
- Cost-effective and environmentally friendly due to lower material usage and energy consumption.
- Better sound insulation properties compared to solid bricks.
- Aesthetic appeal due to a variety of colors, textures, and sizes available
Disadvantages of hollow bricks
1. Lower durability
Due to the presence of air pockets, hollow bricks are less dense compared to solid bricks, which can make them less durable over time.
2. Moisture absorption
The air pockets in hollow bricks can make them more susceptible to moisture absorption, which can lead to issues like mold growth and efflorescence.
3. Limited load-bearing capacity
While these bricks do provide better load-bearing capacity compared to solid bricks, they may not be suitable for certain heavy load-bearing applications.
4. Limited availability
These bricks are not as widely available as solid bricks in certain regions, which can make them more expensive or difficult to source.
5. Specialized installation
Due to their lightweight nature, these bricks require specialized installation techniques and materials, which can increase construction costs.
Uses of hollow bricks
- Load-bearing walls in residential and commercial buildings.
- Partition walls in interior spaces.
- Facades and cladding for exterior walls.
- Retaining walls and garden walls
- Landscaping and garden projects such as planters and raised garden beds
- Archways and decorative features.
- Insulation for HVAC and plumbing systems
