What is the standard rate of load application?

Load must be applied uniformly at a rate of 14 N/mm²/min until failure.

How is the brick frog prepared before testing?

The brick is soaked for 24 hours, the frog is filled flush with 1:3 cement-sand mortar, kept under damp jute bags for 24 hours, and then soaked in water for 3 days.

Which face of the brick should point upwards during the CTM test?

The face with the filled frog should point upwards.

How is the area calculated for compressive strength?

Measure the overall dimensions (length and width) of the two bed faces and take the average of the two areas.

IS 3495 Part 1

: 1992

Methods of Tests of Burnt Clay Building Bricks: Part 1 Determination of compressive strength

CurrentEssentialTesting MethodMaterials Science · Masonry and Bricks

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This standard outlines the laboratory method for determining the compressive strength of burnt clay building bricks. It provides specific instructions for specimen preparation, including the proper filling and curing of the frog, and details the uniform load application process.

Specifies the procedure for determining the compressive strength of burnt clay building bricks.

Quick Reference Values

Initial immersion time before frog filling24 hours

Mortar mix for frog filling1:3 (cement:clean coarse sand)

Curing time under damp jute bags24 hours

Immersion time in water after initial curing3 days

Plywood sheet thickness between brick and platens3 mm

Rate of loading14 N/mm²/min (140 kgf/cm²/min)

Key Formulas

Compressive Strength (N/mm²) = Maximum Load at Failure (N) / Average Area of Bed Faces (mm²)

Practical Notes

Bricks must be tested flat-wise with the frog facing upward.

The mortar filling the frog must be perfectly level and flush with the surface to prevent eccentric or point loading during the test.

Always use 3mm plywood sheets between the brick bed faces and the machine platens to absorb minor surface irregularities.

Wipe off surplus surface moisture before placing the brick in the testing machine.