Making Concrete Test Specimens – essential preparation steps When preparing concrete specimens for strength testing, which of the following steps are necessary before and during casting?

Introduction / Context:
Standard preparation of test specimens is critical for obtaining reliable and comparable strength results. Poor mixing sequence, un-oiled moulds, or non-uniform water addition can introduce variability unrelated to the mix itself, undermining quality control decisions.

Given Data / Assumptions:

• Cubes or cylinders are to be cast according to established standards.
• Materials are proportioned by a qualified mix design and measured accurately.
• Compaction will be carried out by tamping or vibration as specified.

Concept / Approach:

The usual sequence is: dry-mix cement and sand for uniform distribution of fines; add coarse aggregate and mix again to achieve a consistent dry blend; then add measured water (and admixtures if used) and mix until uniform. Moulds must be clean and lightly oiled to prevent bonding to the sides and to obtain smooth faces without defects. Proper stepwise preparation minimizes segregation and ensures consistent specimen integrity.

Step-by-Step Solution:

Verification / Alternative check:

Laboratory SOPs and codes specify this sequence and require clean, lightly oiled moulds; deviations increase scatter in test results.

Why Other Options Are Wrong:

Each individual step is necessary; choosing fewer than all omits essential parts of the standard procedure.

Common Pitfalls:

Adding water first, which causes cement balling; failing to oil moulds; inconsistent mixing times; neglecting aggregate moisture corrections.

Final Answer:

All of the above