Cover blocks and their importance in reinforcement

What is Cover blocks?

Cover blocks are small, sturdy, concrete, or plastic elements. They’re used in construction to ensure the metal bars inside structures (reinforcement) stay in the right place when concrete is poured around them. 

Think of them as little spacers that help keep everything in position.

Importance of Cover Blocks in Reinforcement

Cover blocks might seem small, but they play a huge role in making buildings strong and long-lasting. 

Here’s why they are so important:

1. These help shield metal bars inside buildings, preventing rust and ensuring long-term strength.

2. They enhance overall structure durability, allowing it to endure diverse weather conditions without damage.

3. Maintaining correct distance during construction, and cover blocks are crucial for ensuring the building’s strength.

4. It prevents rust and maintains proper spacing, ensuring buildings remain strong and durable for an extended period.

5. It offers thermal insulation, protecting reinforcement bars from fire damage. This additional layer enhances safety and structural resilience.

Types of cover blocks

There are several types of cover blocks used in construction to ensure the proper spacing and protection of reinforcement bars. 

Here are common types:

1. Concrete Cover Blocks
2. Fiber-reinforced polymer (FRP) Cover Blocks
3. Plastic Cover Blocks
4. Cement Masonry Cover Block
5. Aluminum Cover Block
6. Stone Cover Block

1. Concrete Cover Blocks:

Concrete cover blocks are crucial in reinforced concrete construction, ensuring the correct spacing between reinforcement and concrete surfaces. 

These blocks, typically made of concrete, safeguard against corrosion, enhancing structural durability and strength.

2. Fiber-reinforced polymer (FRP) Cover Blocks:

FRP cover blocks, composed of fiber-reinforced polymers, provide a corrosion-resistant alternative to traditional options. 

Their high strength-to-weight ratio and durability make them well-suited for construction in harsh environments.

3. Plastic Cover Blocks:

Lightweight and corrosion-resistant, plastic cover blocks, often made from high-density polyethylene, offer ease of handling and protection for reinforcement. 

They are adaptable to various designs and construction projects.

4. Cement Masonry Cover Block:

Cement masonry cover blocks, manufactured using cement mortar, are employed in masonry structures to ensure proper spacing and protection for reinforcement. 

They contribute to the structural strength of the reinforcement.

5. Aluminum Cover Block:

Lightweight and corrosion-resistant, aluminum cover blocks, crafted from aluminum alloys, are easy to install and ideal for various construction applications. 

Their durability makes them particularly suitable for structures in coastal or industrial buildings.

6. Stone Cover Block:

Stone cover blocks, crafted from natural stones like granite or marble, serve both functional and aesthetic purposes. 

They maintain reinforcement cover while adding visual appeal to architectural designs, often chosen for their durability and resistance to weathering.

Grades of cover blocks

In construction, cover blocks come in different types, and we grade them to know how good they are. This grading is like giving them a mark based on how strong and good they are for certain jobs. 

Let’s look at one type, the Standard Concrete Cover Blocks:

Standard Concrete Cover Blocks:

The cover blocks are different grades of concrete like M15, M20, M25, M40, and M50, which tell us how strong the concrete is.

Applications:

In construction, it’s common practice to match the grade of concrete block with the grade of reinforcement being used. 

This means that if you’re using a specific grade of concrete for your building blocks, you would also use the same grade for the reinforcement. 

For example, if you have a higher-grade concrete block like M25, you would pair it with M25-grade reinforcement. 

This ensures that the block and the reinforcement have similar strength characteristics, creating a more consistent and reliable structure.

Shapes of cover blocks

Here are the different shapes of cover blocks listed in point form:

1. Cubical cover blocks
2. Circular cover blocks
3. T-shaped cover blocks
4. L-shaped cover blocks
5. Y-shaped cover blocks
6. Slab bolster cover blocks
7. Cylinder or wheel-shaped cover blocks
8. Circular spacers
9. Stool cover blocks (Chair Type Concrete Cover Block)

1. Cubical Cover Blocks:

These are designed to provide uniform spacing between the reinforcement and the concrete surface.

Applications: Columns, Beams, footings

2. Circular Cover Blocks:

These offer a different geometric option for maintaining the required concrete cover over reinforcement.

Applications: Commonly used in columns, slabs, and areas with circular reinforcement patterns.

3. T-Shaped Cover Blocks:

These are shaped like the letter ‘T’ and are effective in providing support and stability to the reinforcement.

Applications: Suitable for beams, footings, and other structural components requiring elevation.

4. L-Shaped Cover Blocks:

These are shaped like ‘L’, and are commonly used to maintain the specified distance between the vertical and horizontal reinforcement.

Applications: Used in columns, and walls

5. Y-Shaped Cover Blocks:

These are shaped like ‘Y’, and are designed to provide support to both horizontal and vertical reinforcement in a structure.

Applications: Columns, Beams, footings

6. Slab Bolster Cover Blocks:

Specifically designed for supporting and spacing the bottom reinforcement in slabs, ensuring proper concrete cover.

Applications: Used in slabs to maintain the required spacing and elevation of reinforcement.

7. Cylinder or Wheel-Shaped Cover Blocks:

These blocks are easy to handle and provide adequate spacing for reinforcement.

Applications: Commonly used in various structural elements (Beams, Columns, etc.), especially where circular reinforcement patterns are present.

8. Circular Spacers:

Similar to circular blocks, these spacers offer additional options for maintaining the correct distance between reinforcement and concrete.

Applications: Used in columns, beams, and slabs to ensure proper alignment and support.

9. Stool Cover Blocks (Chair Type Concrete Cover Block):

These blocks, often resembling a chair, are used to support and maintain the position of the reinforcement in vertical elements such as columns.

Applications: Used in columns, footings, and areas requiring elevated support for reinforcement.

Size of cover blocks

Here are some common cover block sizes you might find in the market, and they help make sure things are strong and last a long time.

Cover Block Type	Size Range (in mm)
Cubical	20mm, 25mm, 30mm, 35mm, 40mm
Circular	Diameter: 20mm, 25mm, 30mm, 35mm, 40mm
T-shaped	20mm x 20mm, 25mm x 25mm, 30mm x 30mm
L-shaped	20mm x 20mm, 25mm x 25mm, 30mm x 30mm
Y-shaped	30mm x 30mm, 35mm x 35mm, 40mm x 40mm
Slab Bolster	Height: 20mm, 25mm, 30mm
Wheel/Cylinder Blocks	Diameter: 20mm, 25mm, 30mm, 35mm, 40mm
Circular Spacers	Diameter: 5mm, 10mm, 15mm
Stool	20mm x 20mm, 25mm x 25mm, 30mm x 30mm

Recommended Cover thickness as per IS 456:2000

Application	Recommended Cover Thickness (mm)
Slabs	20 mm
Staircase	15 mm
Water Retaining Structures	20/30 mm
Retaining Walls	20/25 mm
Flat Slab	20 mm
Beams	25 mm
Columns	40 mm
Strap Beam	35 mm
Shear Wall	25 mm
Raft Foundation (Bottom and Side)	50-80 mm

Advantages Of Concrete Cover Blocks

1. Corrosion Protection

These blocks act as a barrier, preventing direct contact between reinforcement bars and environmental factors, and reducing the risk of corrosion.

2. Durability

They contribute to the longevity of structures by providing protection to reinforcement, ensuring a robust and lasting construction.

3. Proper Spacing

It helps in maintaining the correct distance between reinforcement bars during the concrete pouring process, ensuring structural strength.

4. Easy to Handle

These are lightweight and easy to handle during construction, facilitating efficient installation.

5. Versatility

Available in various shapes and sizes, concrete cover blocks are versatile and can be adapted for use in different construction applications.

Disadvantages Of Cover Blocks

1. Labor Intensive

Installing these can be labor-intensive, especially in large construction projects, which may increase labor costs.

2. Potential Misalignment

Improper installation may lead to misalignment of cover blocks, impacting the effectiveness of reinforcement and structural strength.

3. Material Compatibility

In some cases, ensuring compatibility between the cover block material and the surrounding concrete mix is crucial to avoid issues like differential thermal expansion.

FAQs based on cover blocks