Trial mixes — identify the incorrect practice for preliminary concrete tests While conducting preliminary (trial) mix tests to establish proportions, which of the following statements is NOT correct?

Introduction / Context:
Preliminary (trial) mixes simulate field conditions to calibrate workability, strength, and durability. Correct laboratory practices ensure results are representative of site performance and meet code requirements for temperature and curing.

Given Data / Assumptions:

• Standard mortar/concrete cube preparation per IS practice.
• Ambient laboratory conditions intended to mirror site mixing and curing.
• Temperature control for specimens follows code recommendations.

Concept / Approach:

Codes typically specify 27° ± 2°C for mixing water and curing temperature ranges for specimens, not 37° ± 2°C. Keeping ingredients at excessively high temperatures accelerates setting and can distort workability and strength outcomes. Using the intended proportions/water content, maintaining uniform mixing (even by hand for small batches), and protecting fresh specimens prior to standard curing are acceptable practices (with proper moulding and covering, not sealed “air-tight storage” of unhardened concrete).

Step-by-Step Solution:

Verification / Alternative check:

IS-based procedures describe temperature control around 27° ± 2°C for water and curing tanks for standard-strength determination.

Why Other Options Are Wrong:

• Only (d) states an incorrect temperature; others align broadly with good practice for trials.

Common Pitfalls:

• Conducting trials at unrealistic temperatures leading to misleading water demand and strength results.

Final Answer:

Maintain concrete ingredients at a controlled temperature of about 37° ± 2°C during testing.