When estimating reinforced cement concrete (RCC) works, what cover assumptions are adopted: (i) at the end of a reinforcing bar, (ii) for thin slabs, and (iii) for longitudinal bars in a beam?

Introduction / Context:
Concrete cover is the thickness of concrete between the surface and the nearest reinforcement. Correct cover is vital for durability (corrosion, fire) and for ensuring that reinforcement develops the required bond. Estimation uses assumed covers to derive net dimensions, bar schedules, and quantities.

Given Data / Assumptions:

• Ordinary RCC members: slabs and beams.
• Typical minimum covers for ends, thin slabs, and beam longitudinal bars.
• Cover criteria are expressed as minimums or as functions of bar diameter.

Concept / Approach:
At bar ends and in aggressive exposures, larger cover may be required; however, estimation adopts standard minimums unless specifications dictate otherwise. For thin slabs, the practical lower bound is 12 mm or one bar diameter, whichever is more, to ensure bond and to account for tolerances. For beam longitudinal bars, 25 mm or the largest bar diameter (whichever is greater) is a common baseline before exposure-based adjustments.

Step-by-Step Solution:
1) State end-cover rule: 25 mm or 2d (d = bar diameter) whichever is greater.2) State thin slab rule: 12 mm minimum or d, whichever is greater.3) State beam longitudinal rule: 25 mm minimum or largest bar diameter, whichever is greater.4) Apply these values consistently while preparing bar bending schedules and net formwork dimensions.

Verification / Alternative check:
Design codes allow modifications based on exposure class or fire rating, but the above serve as standard estimation assumptions for general conditions.

Why Other Options Are Wrong:

• Each individual statement is correct; the comprehensive answer requires acknowledging the full set.

Common Pitfalls:

• Confusing nominal cover with clear cover (to links/stirrups vs main bars).
• Ignoring tolerance and exposure adjustments leading to under-cover in practice.

Final Answer:
All the above.