Concrete Blocks – Its Types, Uses and Manufacturing Process

Concrete Masonry Unit (CMU)

Concrete Blocks are also known as Concrete Masonry Units (CMU) or Cement Blocks. These are the standard-sized rectangular blocks used in many construction works. These blocks are the advanced version of brick and stone masonry.

These blocks can be manufactured in any size and shape, they can be solid or hollow according to the requirement. Cement, aggregate and water are the main components of these concrete masonry units. The ratio of cement and aggregate in concrete blocks should be 1:6.

Also, the aggregates used should be 60% fine and 40% coarse aggregates. The minimum strength of these masonry units should be 3 N/mm². These blocks if made up of fly ash, then can be used for the outside fire pit. In India, clay bricks are mostly used for construction projects. Clay bricks are 2-3 times stronger than these concrete blocks.

Types of Concrete Blocks

On the basis of their size, shapes and manufacturing process these blocks can be classified into the following types:

1. Solid Concrete Blocks

These are the most commonly used concrete blocks. The general dimension (in cm) of these blocks are 40 (length) × 20 (width) × 20 / 15 / 10/ 8 (thickness). The minimum density of these concrete blocks is 1800 Kg/m³.

• These concrete blocks have High compressive strength.
• These blocks are good resistance to weathering.
• These blocks have the capability to be molded into any shape or size of the components.
• These blocks also have good fire-resistant properties. These blocks have the capability to handle temperatures up to 400°C.
• These blocks have good stability.
• These blocks are also used in rapid construction works.
• These concrete blocks can be used for the construction of retaining walls.

2. Hollow Concrete Blocks

These concrete blocks can be larger in size as compared to Solid concrete blocks. The general dimension (in cm) of these blocks are 40.5 × 29 × 14. The minimum density of these blocks is 1500 kg/m³.

• These blocks are lighter in weight.
• These concrete blocks are also easy to construct walls.
• The voids in these blocks can be filled up with steel and concrete.
• These cement blocks can achieve high earthquake-resistant properties when filled with steel and concrete in it.
• The air spacing between these blocks can provide better thermal insulation.
• The spacing between these blocks can be used for the electrical and plumbing insulation.
• These blocks are present in different sizes and can be made up according to the requirement.
• These blocks come in 3 grades:
  1. Grade A
  2. Grade B
  3. Grade C
• In which Grade A hollow concrete blocks have a minimum density of 1500 kg/m³ and Grade B blocks has a density of less than 1500 kg/m³ and Grade C has a density of more than 1000 kg/m³.

3. Cellular Concrete Blocks

These concrete blocks have more than one void or spacing for the insulation process. This can be of any size having a spacing of more than one and does not fully penetrate the block. Sometimes it is also known as “Cellular Light Weight Concrete“.

4. Special Concrete Blocks

These are the concrete blocks which are specially manufactured for special purposes according to the requirement. These blocks can be any size, shape and structure which varies from standard sizes and shapes.

Solid Concrete Blocks Vs Hollow Concrete Blocks

Solid Concrete Blocks	Hollow Concrete Blocks
These blocks are solid in nature.	These concrete blocks have one or more hollow spaces on them.
These blocks have a minimum density of 1800 kg/m³.	These blocks have a minimum density of 1500 kg/m³.
The general dimensions of these blocks are 40 × 20 × 20, 40 × 20 × 15, 40 × 20 × 10, and 40 × 20 × 8 (in cm).	The general dimensions of these blocks are 40.5 × 29 × 14 (in cm).
These blocks are heavy in weight.	These blocks are lighter in weight.

Also Read: What is Lightweight Concrete?

Types of Solid Concrete Blocks

Solid concrete blocks are of the following types:

1. Fly Ash Block

Fly Ash is powdery material produced from the burning of pulverized coal. Fly Ash acts as a resource material for many cement products and building products manufacturing companies.

The use of Fly Ash in the concrete helps in the reduction of the emission of CO2, and also reduces cracking problems and permeability. It can also be used to create a smooth surface of the structure. Fly Ash blocks are generally small in size because these blocks get less durable if their size is made bigger.

2. AAC Block

AAC stands for Aerated Autoclaved Blocks. AAC blocks have a density of 350 kg/m³. These blocks are used as load-bearing construction materials. These blocks are good for thermal insulation purposes.

3. Paving Block

These are the concrete blocks used in road shoulders and in walkways. These are used and painted in such a way that they are visible from a distance and make the boundary for vehicles on road. These blocks can be of any shape such as square, rectangular, etc. according to the requirements.

4. Cellular Lightweight Block

These blocks are made up of fly ash, cement and foam. These blocks are lightweight and provide good insulation against sound and heat. These blocks are light grey in colour and are of high and medium density.

5. Expanded Clay Aggregate Block

These blocks are made up of lightweight aggregate, fly ash and cement. These are fire-resistant and waterproof in nature. These blocks also provide good insulation against heat and sound. These are prepared in a kiln at high temperatures. It can be molded into different shapes and sizes.

Types of Hollow Concrete Blocks

1. Stretcher Block

These hollow blocks are mainly used in corner construction. These blocks can be of any size according to the need of construction. Also, these blocks are very light in weight.

2. Pillar Block

These blocks are also known as Double Corner Blocks. These blocks are mainly used for the construction of pillars or piers. These blocks are made up in such a way that they can be left visible from both of its ends. These are also available in various varieties.

3. Lintel Block

These blocks are also known as Channeled Blocks or Beam Blocks. These blocks are of U – shape. These blocks are mostly used on the top of the doors and windows. Mostly used in the construction of lintel beams.

4. Jamb Block

These are the types of hollow concrete blocks that provide the space for the casing of the windows.

5. Column Block

These are the blocks which are present in the shape of a square with a single hole and stacked with the help of reinforcement inside.

6. Corner Block

As the name indicates, these blocks are used only at corners, at the ends of the windows and at door openings. The plain side of the block is exposed to the outer part of the structure.

7. Split Face Block

These blocks are almost similar to pillar blocks but one side of these blocks is very rough. These blocks are very porous in nature and because of this nature, these blocks are vulnerable to water damage. The size of these blocks is 6×8×16 and 8×4×16  inches.

8. Bullnose Block

These blocks are almost similar to the corner blocks. The only difference is that these blocks have rounded edges. And because of the round edges of these blocks, they are known as Bullnose blocks. The size of these blocks is 8×8×16 inches.

9. Partition Block

As the name indicates, these blocks are used in the work of partition. These blocks are similar to concrete pillar blocks but these blocks are taller in size.

Also Read: Hollow Bricks

Manufacturing Process of Concrete Blocks

Manufacturing of concrete blocks involves the following steps:

#1 Mixing

The required amount of sand, aggregates and cement are mixed properly in the mechanical tool. When the dry mixture is prepared properly small amount of water is added to it.

Also the admixtures, coloring substances, etc. according to the requirements are added at this time to the mixer.  It is thoroughly mixed for 6 – 8 minutes.

#2 Molding

After mixing properly the mixture is poured into the molds of the required shapes and sizes. Also before filling up mold with the mixture make sure that the mold was properly cleaned if not then first clean the mold and after that fill it with the concrete mixture. A required amount of pressure is applied to the molds or compacted boxes.

#3. Curing

• When the molds are conveyed out from loading the next process is the curing process.
• For curing, molds are transferred to the curing kiln. Where the molds are left at room temperature for 2 – 3 hours for slight hardening of concrete.
• After a few hours, the steam is released into the kiln for curing the concrete.
• The standard temperature of the steam is 16°C.
• For standard-weight blocks, the temperature of the steam is 66°C to 74°C.
• For lightweight concrete blocks, the temperature of the steam is 77°C to 85°C.
• When the curing temperature is reached the steam is shut off and the molds are left under hot moist air for 12 – 18 hours.
• The total process of curing takes almost 24 hours.

#4. Cubing

Now the blocks are unstacked from the molds and sent to the cuber in which blocks are aligned in such a way that they are shaped to the proper cube or required shape.

What are Cinder Blocks?

These are hollow rectangular blocks made up of coal cinders along with a mixture of concrete. These blocks are also very light in weight. Also when compared with concrete blocks, these blocks have less tensile strength and less load-bearing capacity.

These blocks are most suitable for structures like a garden walls, etc. These blocks are almost old-fashioned blocks. The size of these blocks is 8×8×16 inches.

Difference between Cinder Blocks and Concrete Blocks

Cinder Blocks	Concrete Blocks
These blocks are made up of cement, coal cinders or fly ash.	These blocks are made up of cement, sand and gravel or aggregate.
These blocks are very light in weight.	These blocks are heavier than cinder blocks.
These blocks have low tensile strength.	These blocks have high tensile strength.
These are used in small and light construction such as garden walls, partition walls, etc.	These blocks are used in major construction such as buildings or any other project.
These blocks need more repairing.	These blocks are affordable compared to cinder blocks.
These blocks have only hollow structures.	These blocks can be of any shape or size.
These blocks are very old-fashioned blocks.	Nowadays, these blocks are more likely to be used in construction projects.
These blocks are very inflexible.	These blocks are very strong compared to cinder blocks.

Also Read: Fly Ash Bricks vs Red Bricks