What is the standard size of the cube used in the compressive strength test of cement mortar as per IS code?
- A50 mm × 50 mm × 50 mm
- B70.6 mm × 70.6 mm × 70.6 mmCorrect
- C100 mm × 100 mm × 100 mm
- D150 mm × 150 mm × 150 mm
Solution
Concept
Standard mortar cube dimensions for cement testing as per Indian Standards.
Step-by-step solution
1. Identify the standard code for compressive strength of hydraulic cement: IS 4031 (Part 6). 2. Refer to the specifications for the preparation of mortar cubes using standard sand. 3. Note the dimensions of the cube mould: 70.6 mm size, corresponding to an effective cross-sectional area of 50 sq.cm. 4. Match with the given options to select option (B).
Explanation
As per IS 4031 (Part 6) / IS 650, the standard size of the cube mould used for testing the compressive strength of cement mortar is 70.6 mm × 70.6 mm × 70.6 mm. This provides a face area of exactly 50 cm², which simplifies calculation of compressive stress when tested in a compression testing machine.
Why the other options are wrong
A: 50 mm × 50 mm × 50 mm is not the standard size as per IS codes for cement mortar strength. C: 100 mm × 100 mm × 100 mm is sometimes used for specific concrete tests or lightweight concrete, not standard cement mortar. D: 150 mm × 150 mm × 150 mm is the standard size for concrete cube compressive strength tests.
Shortcut
Remember that cement mortar cubes are 70.6 mm (giving 50 cm² area), whereas concrete cubes are larger at 150 mm.
Common mistake
Confusing cement mortar cube size (70.6 mm) with standard concrete cube size (150 mm) or standard permeability/mortar briquette sizes.
Correct answer: B) 70.6 mm × 70.6 mm × 70.6 mm