Reinforcement (steel bars) used in concrete work must be clean and free from contaminants State what the bars must be free from before placement to ensure proper bond and durability.

Introduction:
Clean reinforcement is essential for achieving proper bond between steel and concrete. Contaminants can reduce bond strength, increase slip, and compromise durability. This question checks basic site workmanship requirements.

Given Data / Assumptions:

• Reinforcement is carbon steel bars intended for reinforced concrete.
• Surface condition affects bond and corrosion risk.

Concept / Approach:

Standards require bars to be free from loose mill scale, loose rust, paint, oil, mud, or any deleterious coating that prevents adhesion. A thin, tight rust film is typically acceptable, but loose flaky rust is not.

Step-by-Step Solution:

Verification / Alternative check:

Pull-out tests and site inspections confirm that clean, roughened metal surfaces provide better bond.

Why Other Options Are Wrong:

Choosing only one contaminant underestimates the requirement; all listed items are harmful to bond if present.

Common Pitfalls:

Leaving oil from cutting/greasing on bars or painting bars for identification without removing paint lines in bond zones.

Final Answer:

all the above