How to determine the Compressive Strength of a Brick?

Compressive strength of a brick is determined by testing the brick under standard conditions using a Compression testing machine. The procedure as mentioned in IS 3495 (Part-2) shall be used to determine the compressive strength of brick work.

The following apparatus is required for testing the brick:

  1. Measure scale
  2. Compression Testing Machine

The minimum compressive strength required for a Burnt Clay Brick as per IS code is 3.5 N/mm2.

Compression Testing Machine

Compression Testing Machine

Number of Brick Specimens to be collected

Five (5) number of burnt clay bricks are to be tested and the average compressive strength value has to be reported.

Refer IS-5454 for sampling of bricks for compressive strength test

Preconditioning of Bricks Before Testing Procedure

The following steps are to be done on all the specimens before they are

  1. Measure the dimensions of the top surface (frog side) of the brick to the nearest 1 mm.
  2. Remove any unevenness observed on the bed faces (i.e., frog side and on the opposite side) by grinding.
  3. Immerse the brick in water for a period of 24 hours. The specimen should be then removed and excess water is drained out at room temperature.
  4. The frog portion and voids on the top surface if any has to be filled with cement mortar (1 cement,1 clean coarse sand of grade 3mm and down).
  5. Store the brick under a damp jute bag for 24 hours. Following this immerse the brick in clean water for a period of 3 days. Remove and wipe out any traces of moisture in the brick

Procedure for Testing Compressive Strength of Bricks

  • Place the specimen prepared with flat faces horizontal and mortar filled faces (i.e., frog face) upwards between two 3mm plywood sheets and carefully centred between plates of testing machine. The plywood sheets will ensure that the load is transferred uniformly.
  • Now apply axial load at a uniform rate of 14 N/mm2 (or 140 kgf/cm2) per minute till failure occurs.
  • Note the maximum load at failure and repeat the procedure for other specimens
Compressive Strength test for Brick

Compression test of a Brick specimen

Compressive Strength Calculation

Compressive strength of the brick is calculated in the following way.

Brick Compressive Strength Formula

The average of the 5 specimens have to be reported as the compressive strength of the bricks in the lot.