Time window for handling OPC concrete: For mixes using Ordinary Portland Cement without set-retarding admixtures, the total time from mixing through transport, placement, and compaction should not exceed

Introduction / Context:
Ordinary Portland cement begins to lose workability as hydration proceeds. In site practice without retarders and under normal temperatures, concrete should be placed and compacted before significant stiffening to avoid honeycombing and cold joints.

Given Data / Assumptions:

• OPC used, no set-retarding admixtures.
• Normal ambient temperatures and transport distances.
• Focus is total elapsed time from water addition.

Concept / Approach:
Initial set of OPC typically occurs near 30 minutes to several tens of minutes depending on cement and temperature. To maintain full consolidation and bond between lifts, conventional guidance limits mixing-to-placing time to about 30 minutes when no admixtures are used. Longer times are acceptable only with retarders, controlled temperatures, or ready-mix specs designed for extended haul.

Step-by-Step Solution:
Identify cement type and absence of retarders → rapid loss of workability.Adopt conservative site limit for mixing-to-placement.Select 30 minutes.

Verification / Alternative check:
Hot-weather guidance further shortens the allowable time; admixtures can extend it to 60–90 minutes in ready-mix operations, but that is outside this question’s premise.

Why Other Options Are Wrong:
Longer durations assume retardation or special controls not stated.

Common Pitfalls:
Re-tempering concrete with water to regain slump; this compromises strength and durability.

Final Answer:
30 minutes.