Compressive strength test of cement mortar — identify the incorrect statement (IS practice) Which ONE of the following statements is incorrect for the standard compressive strength test of cement mortar cubes as per Indian practice?

Introduction / Context:
Standardized testing of cement strength uses specified materials, proportions, specimen sizes, and curing regimes. Small deviations can significantly alter results, so it is important to know the correct procedure and parameters used in the compressive strength test of cement mortar cubes.

Given Data / Assumptions:

• Indian Standards test method for cement mortar (standard sand) compressive strength.
• Standard consistency P determined by Vicat.
• Controlled curing temperature and initial storage conditions.

Concept / Approach:
Cement strength is evaluated using mortar cubes made with standard sand at a 1:3 ratio. The commonly used cube size for cement mortar strength testing is about 70.6 mm (not 100 mm), ensuring a standard loaded area of roughly 50 cm². Mixing water is taken as (P/4 + 3) percent of the total mass. After demoulding at about 24 hours, cubes are cured in water at 27° ± 2°C until the test age.

Step-by-Step Solution:

Verification / Alternative check:
Laboratory manuals and IS methods specify 70.6 mm mortar cubes (not 100 mm) for cement strength tests with standard sand.

Why Other Options Are Wrong:

• Options (a), (b), (d), and (e) align with standard practice; they are not incorrect.

Common Pitfalls:
Mixing up cement-mortar cube size with concrete cube size; misapplying the water formula intended for the specific mortar test.

Final Answer:
Cube mould of side 100 mm is used for the cement mortar strength test.