End cover for reinforcing bars (bar termination): The minimum thickness of cover at the end (terminating face) of a reinforcing bar should be at least twice the bar diameter, subject to a lower bound not less than which absolute value?

Introduction / Context:
Concrete cover protects reinforcement from corrosion and fire and provides adequate anchorage. At the bar termination (ends), cover must be sufficient to prevent splitting and spalling and to allow effective transfer of bond stresses.

Given Data / Assumptions:

• Cover at the end face where a reinforcing bar terminates.
• Rule: cover ≥ 2 × bar diameter with a minimum absolute value.
• Typical building exposure conditions assumed.

Concept / Approach:
Many detailing guides prescribe that end cover should not be less than twice the bar diameter and, additionally, should not be less than an absolute minimum such as 25 mm. This ensures that the concrete cone around the bar end is robust and bond transfer is reliable.

Step-by-Step Reasoning:
Compute 2d for the bar in question.Compare with the absolute minimum (25 mm) and adopt the larger value.Provide proper compaction and avoid cutting bars too close to the end face.

Verification / Alternative check:
Project specifications may increase cover for harsh exposures; however, the 25 mm absolute minimum is a widely cited baseline in many exam contexts for normal exposures.

Why Other Options Are Wrong:
10, 15, 20 mm: Too small as an absolute minimum for bar ends in typical structural members.30 mm: May be specified for severe exposure, but the baseline minimum used in such questions is 25 mm.

Common Pitfalls:

• Confusing side cover, top/bottom cover, and end cover requirements.
• Not accounting for concrete tolerance when detailing end cover.

Final Answer:
25 mm