Classification of Bricks by Field Practices
Clay bricks are categorized into four classes—first class, second class, third class, and fourth class—depending on their physical and mechanical attributes observed during field practices:
First Class Bricks
Thorough Burning: First-class bricks exhibit a deep red, cherry, or copper color, indicating thorough burning during production.
Surface Quality: Their surfaces are smooth, rectangular, with sharp, straight edges, and precise square corners.
Flawless Structure: They must be free from flaws, cracks, and stones, ensuring structural integrity.
Uniform Texture: Consistency in texture throughout the brick is essential for quality.
Indentation Resistance: No impression should remain when a fingernail scratches the brick.
Fracture Characteristics: The fractured surface should not reveal lumps of lime, indicating proper composition.
Auditory Test: When struck against each other, they produce a metallic or ringing sound, indicating density and strength.
Water Absorption: After 24 hours in cold water immersion, water absorption should range between 12–15% of the brick’s dry weight.
Crushing Strength: A minimum crushing strength of 10 N/mm2 is required. This standard might vary across different government organizations in the country.
Recommended Uses: First-class bricks find applications in pointing, exposed face work in masonry structures, flooring, and reinforced brickwork due to their superior quality and strength.
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Second Class Bricks
Second-class bricks maintain similar requirements to first-class bricks with specific allowances:
- Permitted Imperfections: Small cracks and distortions are acceptable within defined limits.
- Higher Water Absorption: An increased water absorption range of approximately 16–20% of its dry weight is allowed.
- Minimum Crushing Strength: The minimum required crushing strength is 7.0 N/mm2.
Recommended Uses: Second-class bricks are suitable for both important and unimportant hidden masonry works. They are also ideal for use in the centering of reinforced brick and reinforced cement concrete (RCC) structures.
Third Class Bricks
Third-class bricks exhibit distinct characteristics due to being underburnt:
- Underburnt Nature: These bricks are underburnt, resulting in a soft and light-colored appearance.
- Auditory Characteristics: They produce a dull sound when struck against each other.
- Higher Water Absorption: Their water absorption rate is approximately 25% of their dry weight.
- Minimum Crushing Strength: The minimum required crushing strength stands at 3.5 N/mm2.
Recommended Uses: Third-class bricks are typically utilized in the construction of temporary structures due to their underburnt nature and lower strength.
Fourth Class Bricks
Fourth-class bricks possess distinct characteristics due to overburning during their production:
- Overburnt Nature: These bricks are overburnt, resulting in severe distortion in shape and size. They tend to be brittle in nature.
- Usage: Despite their structural shortcomings, these bricks find utility as ballast for foundations, lime concrete, and road metal owing to their composition.
Classification of Bricks on the Basis of Strength
The Bureau of Indian Standards (BIS) has classified the bricks on the basis of compressive strength and is as given in Table below:
IS 1077 - Classification of Bricks Based on Compressive Strength
| Class | Minimum Average Compressive Strength (N/mm²) |
|---|---|
| Class 3.5 | 3.5 |
| Class 5 | 5 |
| Class 7.5 | 7.5 |
| Class 10 | 10 |
| Class 12.5 | 12.5 |
| Class 15 | 15 |
| Class 17.5 | 17.5 |
| Class 20 | 20 |
| Class 25 | 25 |
| Class 30 | 30 |
| Class 35 | 35 |
Each class of bricks specified above is further divided into subclass A and B based on tolerances and Shapes . Subclass A bricks should have smooth rectangular faces with sharp corners and uniform colour. Subclass B bricks may have slightly distorted and round edges.
| Subclass-A | Subclass-B | ||||
|---|---|---|---|---|---|
| Dimension(cm) | Tolerance(mm) | Dimension(cm) | Tolerance(mm) | ||
| Length | 380 | ± 12 | Length | 380 | ± 30 |
| Width | 180 | ± 6 | Width | 180 | ± 15 |
| Height (i) 9 cm | 180 | ± 6 | Height (i) 9 cm | 180 | ± 15 |
| Height (ii) 4 cm | 80 | ± 3 | Height (ii) 4 cm | 80 | ± 6 |
Classification of Bricks on the Basis of Use
Common Bricks
Common bricks serve as versatile, economically manufactured units without emphasis on appearance. They vary widely in strength and durability. Typically utilized for filling, backing, and in walls where appearance holds no significance.
Facing Bricks
Designed primarily for aesthetic appeal, facing bricks prioritize good appearance in terms of color, texture, or both. These bricks endure severe exposure and find application in building fronts where an attractive appearance is desired.
Engineering Bricks
Characterized by strength, impermeability, smoothness, table molding, and hardness, engineering bricks adhere strictly to defined limits of absorption and strength. These bricks are specifically used in all load-bearing structures due to their robust qualities
Classification of Bricks On the basis of finish
Sand-Faced Bricks
Sand-faced bricks feature a textured surface achieved by sprinkling sand on the inner surfaces of the mold during manufacturing. This process results in a rougher texture, adding visual interest and depth to the brick surface.
Rustic Bricks
Rustic bricks exhibit a mechanically textured finish with variations in patterns. This finish is deliberately designed to offer a distinct and uneven appearance, often mimicking the ruggedness found in natural materials.
Additional Finish Varieties
Wire-Cut Bricks: These bricks are cut from clay extruded in a column and then sliced into brick sizes by wires, resulting in a smooth and precise finish.
Pressed Bricks: Manufactured from stiff plastic or semi-dry clay, these bricks are pressed into molds, ensuring uniformity and smooth surfaces.
Moulded Bricks: These bricks are machine-molded to imitate hand mixing, providing varied textures and shapes based on specific requirements.
Classification of Bricks On the basis of Manufacture
Hand-Made Bricks
Handmade bricks are crafted through traditional methods of hand molding. Skilled artisans shape these bricks manually, allowing for a unique and often irregular appearance, adding character to the final product.
Machine-Made Bricks
Machine-made bricks encompass various manufacturing techniques:
Wire-Cut Bricks: Produced by cutting clay extruded in a column into brick sizes using wires. This method yields precise and sharp-edged bricks.
Pressed Bricks: Manufactured from stiff plastic or semi-dry clay, these bricks are pressed into molds, resulting in uniform and smooth surfaces.
Moulded Bricks: Machines replicate hand mixing techniques to mold bricks, offering diverse textures and shapes. These bricks maintain consistency and can simulate handmade qualities.
Classification of Bricks On the basis of Burning
Pale Bricks
Pale bricks are underburnt bricks acquired from the outer portion of the kiln during firing. These bricks tend to have a lighter color and might exhibit characteristics of insufficient firing, resulting in lower strength and durability.
Body Bricks
Body bricks, occupying the central portion of the kiln during firing, are well burnt and adequately fired. These bricks maintain a balanced firing temperature, resulting in consistent strength and durability, making them suitable for various construction applications.
Arch Bricks (Clinker Bricks)
Arch bricks, also known as clinker bricks, are overburnt bricks obtained from the innermost section of the kiln during firing. Due to excessive heat exposure, these bricks often display a distorted shape, darker coloration, and increased brittleness, limiting their structural reliability.
Classification of Bricks On the basis of Types
Solid Bricks
Solid bricks typically feature a structure without extensive perforations or hollow sections. They may allow for small holes not surpassing 25% of the brick’s volume. Alternatively, frogs, which are indentations or recesses on the brick’s surface, should not exceed 20% of the total volume.
Perforated Bricks
Perforated bricks are characterized by their higher number of holes, allowing for small perforations that might surpass 25% of the total brick volume. This design facilitates better ventilation and reduced weight in construction applications.
Hollow Bricks
Hollow bricks feature a considerable number of holes, exceeding 25% of the brick’s volume. These larger cavities reduce the brick’s weight, making them ideal for various construction purposes where weight considerations are critical.
Cellular Bricks
Cellular bricks possess holes closed at one end, exceeding 20% of the brick’s volume. These closed-end holes offer distinct structural benefits while maintaining a certain level of permeability and reduced weight.
