COMPRESSOVE STRENGTH OF BRICKS

The compressive strength of bricks is a critical property that determines the load-bearing capacity of the brick and its suitability for construction.

It is defined as the maximum load per unit area that a brick can withstand before failure. 

This value is measured in megapascals (MPa) or Newtons per square millimeter (N/mm2)

Factors Affecting the Compressive Strength of BricksType of Brick: 

The material composition (clay, fly ash, concrete) and manufacturing process influence strength.

Firing Temperature: For clay bricks, higher firing temperatures increase strength by reducing porosity.

Water Absorption: High water absorption usually indicates a weaker brick.

Density and Porosity: Denser bricks with lower porosity typically have higher compressive strength.

Age of the Brick: The strength of bricks, especially those made from concrete or cement, can increase with curing over time.

Typical Compressive Strengths of Various Brick Types:

Common Burnt Clay Bricks:

Class A: 10.5 – 15 MPa

Class B: 7 – 10.5 MPa

Class C: 3.5 – 7 MPa

Fly Ash Bricks:

Range: 7.5 – 15 MPa

Concrete Bricks:

Range: 3.5 – 20 MPa (depending on mix design and curing conditions)

Engineering Bricks:

Typically over 50 MPa (high strength, used for load-bearing and damp-proof courses)

AAC (Autoclaved Aerated Concrete) Bricks:

Range: 3 – 7 MPa (low strength but lightweight)

Testing Procedure for Compressive Strength of Bricks:

Sample Preparation:

Take a sample of dry bricks (usually 5 specimens).

Ensure the bricks are free from defects.

Test Procedure (IS 3495 Part I, ASTM C67):

Place the brick on a compression testing machine with the flat face horizontally.

Apply load gradually at a rate of 14 N/mm² per minute until the brick fails.

Note the maximum load at failure.

Compressive Strength Formula:

Compressive Strength=Maximum Load (N)Area of Brick (mm²)Compressive Strength=Area of Brick (mm²)Maximum Load (N)​

Example: If the maximum load is 100,000 N and the area of the brick is 10,000 mm², then the compressive strength is:

100,000 N÷10,000 mm²=10 N/mm²(10MPa)100,000N÷10,000mm²=10N/mm²(10MPa)

Standards for Compressive Strength:

IS 1077 (Indian Standard): Minimum compressive strength of 3.5 MPa for common bricks.

ASTM C62 (American Standard): Minimum compressive strength for different grades of brick ranges from 8.6 MPa to 20.7 MPa.

Compressive strength is crucial for assessing brick quality and ensuring structural safety, especially in load-bearing applications.