Short Notes Bricks - Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

Introduction

Bricks are made by shaping clay into rectangular blocks of consistent size, then drying and firing these blocks. Because bricks are uniform in size, they can be arranged easily, are lightweight, and have become a popular substitute for stones in construction.Earthy Construction

Composition of Bricks

• Alumina: This is the main component of all types of clay. A good brick earth should have 20 to 30 percent alumina, which gives the earth its plasticity, making it easy to mold. However, too much alumina can cause raw bricks to shrink and warp during drying and burning.
• Silica: Ideally, brick earth should contain about 50 to 60 percent silica. Silica can be present as free sand, mixed mechanically with clay, or in a chemical composition with alumina. It prevents cracking, shrinking, and warping of raw bricks, ensuring they have a uniform shape. The durability of bricks relies on the right amount of silica; too much silica can make bricks brittle by destroying the cohesion between particles.
• Lime:. small amount of lime in a finely powdered state is beneficial as it prevents shrinkage of raw bricks. However, excess lime can cause bricks to melt and lose their shape due to splitting.
• Iron Oxide:. small quantity of iron oxide (about 5 to 6 percent) is desirable as it imparts a red color to bricks. Too much iron oxide can make bricks dark blue or blackish.
• Magnesia:. small amount of magnesia can give bricks a yellow tint and reduce shrinkage. However, too much magnesia can lead to decay of bricks.Natural Brickmaking

Harmful Ingredients

• Ingredients like lime, iron pyrites, alkalies, pebbles, and organic matter should not be present in good brick earth.

Manufacturing Process of Bricks

The process of manufacturing bricks involves various steps, which are as follows:

1. Preparation of Clay

The initial step in brick manufacturing is the preparation of clay. This involves the following sub-steps:

• Digging: The clay is dug from the ground, usually from a depth of about 1 meter to 2 meters. This depth ensures the extraction of suitable clay for brick making.
• Crushing: The dug-out clay is then crushed to break down any lumps and ensure a uniform texture. This is an essential step as it affects the quality of the bricks.
• Weathering: After crushing, the clay is spread out and left to weather. Weathering involves exposing the clay to the elements, allowing it to undergo physical and chemical changes. This process can take several weeks. Weathering improves the plasticity of the clay, making it easier to mold.
• Mixing: Once the clay has weathered, it is mixed to achieve a uniform consistency. During this stage, water may be added to adjust the moisture content, making the clay pliable and suitable for molding.

Alternative Method: Artificial Weathering : In some cases, especially in large-scale production, the weathering process is done artificially. This involves using machines to replicate the natural weathering process, speeding up the preparation time.

Importance of Preparation: Proper preparation of clay is crucial as it directly impacts the strength, durability, and overall quality of the bricks produced. Well-prepared clay leads to uniform bricks with consistent properties.

2. Moulding

Moulding is a crucial step in the brick manufacturing process where the prepared clay is shaped into bricks. This process can be done using various methods, each with its own advantages. Here are the details of different moulding techniques:Handcrafted Bricks

(a) Hand Moulding

Hand moulding is a traditional method of brick production, commonly used in small-scale and rural industries. Process: In this method, the prepared clay is manually pressed into wooden or metal moulds to form bricks. The moulds are usually coated with sand or oil to prevent the clay from sticking. Advantages: Hand moulding allows for flexibility in production and is cost-effective. It is suitable for making bricks in various shapes and sizes. Disadvantages: This method is labor-intensive and may result in slight variations in brick size and shape.

(b) Machine Moulding

Machine moulding is an advanced method that uses machines to automate the moulding process, ensuring uniformity and precision in brick production. Types of Machine Moulding: There are several types of machine moulding, including: (i) Plastic Clay Machines. These machines have a rectangular opening through which pugged clay is forced. As the clay comes out, it is cut into strips by wires, forming bricks. (ii) Dry Clay Machines. In this method, strong clay is first powdered and then mixed with water to form a stiff paste. This paste is pressed into moulds to create well-shaped bricks. Advantages of Machine Moulding: Machine moulding offers several benefits, such as: (i) Uniformity: Bricks produced are of consistent size and shape. (ii) Efficiency: The process is faster and requires less manual labor. (iii) Quality: Machine-moulded bricks have better texture and carry distinct frogs (indentations).Precision Brick Moulding

3. Drying

After moulding, the damp bricks need to be dried before the burning process. Drying is essential to prevent cracking and distortion during firing. Here are the methods and details of the drying process:

• Artificial Drying: In this method, bricks are dried in tunnels at a temperature of about 1200°C for a duration of 1 to 3 days. This controlled environment accelerates the drying process.
• Circulation of Air: Stacks of bricks are arranged to allow free circulation of air between them. This natural drying method relies on airflow to remove moisture from the bricks.
• Drying Yard: Specially prepared yards, slightly elevated to prevent rainwater accumulation, are used for drying bricks. This method utilizes natural sunlight and air for drying.
• Drying Period: The typical period for drying bricks ranges from 3 to 10 days, depending on the method used and environmental conditions.
• Screens: Screens may be used to avoid direct exposure of bricks to wind or sun, providing a balanced drying environment.Sunlit Drying Bricks

4. Burning

Burning is a critical operation in the manufacturing of bricks as it imparts hardness, strength, and durability to the bricks. There are two main methods of burning: Clamps and KilnsIndustrial Brick Firing

(a) Clamps: These are temporary structures used for small-scale brick production. The process involves:

• Construction:. trapezoidal-shaped clamp is built, with the shorter end slightly excavated and the wider end raised at an angle of 15° from the ground level.
• Layering: Layers of raw bricks and fuel (such as grass, cow dung, wood, or coal) are alternated. The total height of the clamp is about 3 to 4 meters.
• Plastering: The completed clamp is plastered with mud on the sides and top, and filled with earth to prevent heat escape.
• Burning Period: The burning process takes about one to two months, followed by a similar cooling period.
• Advantages of Clamps: Produces tough and strong bricks due to gradual burning and cooling. Cost-effective and requires no skilled labor for construction.
• Disadvantages of Clamps: Bricks may not be of uniform shape and quality. The process is slow, and fire regulation is not possible.

(b) Kilns: These are permanent structures used for large-scale brick production. There are two main types of kilns:

• Intermittent Kilns: These kilns are loaded, fired, cooled, and unloaded in batches. Types include:
• (i) Intermittent Up-Draught Kilns: Rectangular kilns with thick walls, where raw bricks are laid in rows and fuel is added. The kiln is fired for 48 to 60 hours. (ii) Intermittent Down-Draught Kilns: Similar to up-draught kilns, but with a different airflow design. These kilns offer better temperature control and efficiency.
• Continuous Kilns: These kilns operate continuously, with a constant supply of raw bricks and removal of finished bricks. They provide higher efficiency and uniformity in brick production.

Conclusion: The choice of burning method depends on the scale of production, available resources, and desired brick quality. Clamps are suitable for small-scale production, while kilns are preferred for large-scale manufacturing.

Burning of Bricks

The process of burning bricks involves several steps and can be carried out using different types of kilns. Below are the details of the burning process and the types of kilns used.Kiln Firing Process

Burning Process

(i) Preparation: The prepared bricks are loaded into the kiln for burning.

(ii) Firing: The kiln is fired up to initiate the burning process.

(iii) Cooling: After the burning is complete, the kiln is allowed to cool down.

(iv) Unloading: Once cooled, the burnt bricks are taken out of the kiln.

(v) Repetition: The same procedure is repeated for the next batch of bricks.

Types of Kilns

(a) Intermittent Up-draught Kilns:

• These kilns are used for burning bricks intermittently.
• The process involves loading the bricks, firing, cooling, and unloading in batches.
• Advantages: Better quality bricks compared to clamps.
• Disadvantages:
  • Non-uniform burning.
  • Discontinuous supply of bricks.
  • Wastage of fuel heat.

(b) Intermittent Down-draught Kilns:

• These kilns are rectangular or circular with permanent walls and a closed roof.
• The floor has openings connected to a common chimney stack through flues.
• Hot gases are carried through vertical flues to the roof level and then released, moving downward by chimney draught to burn the bricks.
• Advantages:
  • Even burning of bricks.
  • Better performance than up-draught kilns.
  • Suitable for burning structural clay tiles and terra cotta due to close heat control.

  2. Continuous Kilns  

•  Continuous kilns operate with simultaneous loading, firing, cooling, and unloading. 
•  There are three types of continuous kilns: Bull's Trench Kiln, Hoffman’s Kiln, and Tunnel Kiln. 

  a) Bull’s Trench Kiln  

•  Bull’s trench kiln can be rectangular, circular, or oval in shape. 
•  It is constructed in a trench, either fully underground or partially above ground. 
•  The kiln has flue holes in the outer walls, and dampers divide the kiln into sections. 
•  Bricks are arranged to form flues, and fuel is placed in these flues and ignited. 
•  Movable iron chimneys are used to create draught and warm the next section. 
•  Each section requires about one day to burn. 

  b) Hoffman’s Kiln  

•  This kiln is constructed above ground and is sometimes called a flame kiln. 
•  It has a circular shape and is divided into multiple compartments or chambers. 
•  A permanent roof is provided, allowing the kiln to function even during the rainy season. 
•  The initial cost of installing Hoffman’s kiln is high, but it offers several advantages, including: 
•  Producing good quality bricks. 
•  Regulating heat inside the chambers. 
•  Continuous and regular supply of bricks. 
•  Fuel savings due to preheating of raw bricks by flue gases. 

  c) Tunnel Kiln  

•  The tunnel kiln is shaped like a tunnel, which can be straight, circular, or oval. 
•  Raw bricks are placed in trolleys and moved through the kiln from one end to the other. 
•  As the bricks move towards the fire zone, they are dried and preheated. 
•  In the fire zone, the bricks are burnt to the required quality and then pushed forward for cooling. 
•  Once cooled, the bricks are unloaded. 
•  Tunnel kilns are economical for large-scale production and produce uniform, high-quality bricks due to controlled temperatures. 

Comparison between Clamp-Burning and Kiln-Burning

Classification of Bricks

The classification of bricks is based on various parameters such as the method of manufacturing, the type of clay used, and the intended use of the bricks. Here is a detailed explanation of the different types of bricks:

1. First Class Bricks:

• Made from good quality clay and burnt in a kiln, these bricks are well-shaped, of uniform size, and have sharp edges.
• They possess high compressive strength (greater than 140 kg/cm²) and low water absorption (less than 20%).
• First class bricks are used for load-bearing walls, arches, and other structural applications.
• They are also suitable for facing work and in situations where aesthetic appearance is important.

2. Second Class Bricks:

• These bricks are also made from good quality clay, but they may not be as uniform or well-shaped as first class bricks.
• They have a compressive strength of 70 kg/cm² to 140 kg/cm² and water absorption of 20% to 25%.
• Second class bricks are suitable for non-load-bearing walls, partition walls, and other applications where strength is not a critical factor.Clay Textures

3. Third Class Bricks:

• Made from inferior quality clay and burnt at lower temperatures, these bricks are less durable and have lower strength.
• They have a compressive strength of less than 70 kg/cm² and high water absorption (greater than 25%).
• Third class bricks are used for temporary structures, non-load-bearing walls, and other applications where strength and durability are not critical.

4. Special Bricks:

• These bricks are designed for specific applications and have unique properties.
• Examples include fire bricks (used in high-temperature applications), insulating bricks (used for thermal insulation), and engineering bricks (designed for high strength and low water absorption).

In conclusion, bricks are classified based on their strength, durability, and intended use. It is essential to choose the right type of brick for specific applications to ensure structural integrity and longevity.

Bricks for Strength

Types of Special Bricks

1. Fire Bricks: Used in high-temperature environments like kilns and furnaces due to their heat resistance.

2. Hollow Bricks: Lightweight bricks with hollow cores, used for insulation and reducing weight in construction.

3. Fly Ash Bricks: Made from fly ash, a byproduct of coal combustion, these bricks are eco-friendly and have good insulation properties.

4. Glass Bricks: Used for aesthetic purposes and allowing light while maintaining privacy, commonly in walls and partitions.

5. Refractory Bricks: Similar to fire bricks but specifically designed for extreme conditions like in metal smelting.

6. Engineering Bricks: High-strength bricks used in load-bearing walls and areas subjected to high stress.

7. Paving Bricks: Used for outdoor paving due to their durability and aesthetic appeal.

8. Stone Bricks: Made from natural stone, these bricks are used for their strength and natural appearance.

9. Compressed Earth Bricks: Made from compressed soil, these bricks are sustainable and have good thermal properties.

10. Acoustic Bricks: Designed to absorb sound, used in buildings where noise reduction is important.Eco-friendly Bricks

Uses of Bricks

1. Load-Bearing Walls: Bricks provide the necessary strength and stability for load-bearing walls in buildings.

2. Partition Walls: Used to create internal divisions within buildings, offering privacy and sound insulation.

3. Facades: Bricks enhance the aesthetic appeal of buildings while providing weather resistance.

4. Paving: Bricks are used in outdoor paving for their durability and resistance to weather conditions.

Structural Aesthetics

Qualities of Bricks

1. Strength: Bricks should have high compressive strength to withstand loads.

2. Durability: Resistance to weathering and environmental factors is crucial for longevity.

3. Water Absorption: Low water absorption rates indicate better quality and durability.

4. Fire Resistance: Bricks should be able to withstand high temperatures without deforming.

5. Uniformity: Consistent size, shape, and color are important for aesthetic and structural reasons.

6. Workability: Bricks should be easy to handle and lay during construction.

Use of Frog in Bricks

The frog in a brick serves several important purposes:

• Improved Bonding: The frog creates a depression on the top surface of the brick, allowing for better adhesion of mortar. This enhances the bond between bricks and mortar, ensuring a stronger and more durable wall.
• Mortar Retention: The frog helps in retaining mortar within the depression, preventing it from spilling over during the laying process. This ensures that there is enough mortar to fill the joints between bricks, further improving the bond.
• Aesthetic Appeal: The frog can also contribute to the aesthetic appearance of a wall. When bricks are laid with the frog facing up, it creates a uniform surface, enhancing the overall look of the wall.Architectural Aesthetics

Uses of Fire Bricks

1. Kilns: Fire bricks are extensively used in the construction of kilns for pottery, ceramics, and other materials that require high-temperature firing.

2. Furnaces: They are ideal for lining furnaces used in metal smelting and other industrial processes due to their ability to withstand extreme heat.

3. Pizza Ovens: Fire bricks are popular in building pizza ovens as they retain and radiate heat evenly, ensuring perfect cooking temperatures.

4. Barbecues: They are used in constructing barbecue pits and grills where high temperatures are required for cooking.Thermal Innovations

Uses of Hollow Bricks

1. Wall Construction: Hollow bricks are commonly used for building walls due to their lightweight nature and good thermal insulation properties.

2. Partition Walls: They are ideal for creating internal partition walls in residential and commercial buildings, offering sound insulation and privacy.

3. Facade Cladding: Hollow bricks can be used for cladding building facades, providing an aesthetic appeal while reducing the overall weight of the structure.

4. Pavements: These bricks are also used in pavement construction, especially in areas where weight reduction is essential, such as on rooftops or elevated structures.

Size and Weight of Standard Brick

The standard size of a brick is typically 190 mm x 90 mm x 90 mm (length x width x height). The weight of a standard brick can vary depending on the type and material, but it generally ranges from 2.5 kg to 3 kg per brick.

Blending in Bricks

Blending in the context of bricks refers to the process of mixing different types of raw materials or clay to achieve a uniform and desired composition before the manufacturing process. This is done to ensure consistency in quality, color, and other properties of the final brick product. Blending helps in optimizing the characteristics of the bricks, making them suitable for specific applications.

Tempering in Bricks

Tempering is the process of adding water to the raw clay or soil mixture during the brick manufacturing process to achieve the desired consistency and plasticity. This step is crucial as it enhances the workability of the material, making it easier to mold into the desired shape. Proper tempering ensures that the bricks have uniform density and strength after firing.