Which scenario requires immediate action to prevent nonconforming concrete from being placed?

• A. A small color deviation within specification.
• B. A reported air content within limits.
• C. Concrete sample shows excessive air content or other parameters outside specification; place must stop, notify, and testing per contract.
• D. Temperature is slightly above ideal.

Answer: (C)

Nonconforming concrete is material that does not meet the specified properties, so it must be halted to prevent placing defective concrete. When a concrete sample shows excessive air content or any parameter outside the specification, the concrete is outside the allowed tolerances and must not be placed. The correct action is to stop placing, notify the supervisor, and proceed with testing per the contract to determine whether the batch can be corrected or must be rejected.

The other scenarios don’t demand immediate stopping because they either fall within allowable tolerances or are cosmetic/limited in impact on performance. A small color deviation is typically aesthetic and within spec; an air content within limits indicates acceptable quality; a temperature that's slightly above ideal may still be within the permitted range and not require stopping. The key rule is: stop placement whenever a property is outside the spec to prevent nonconforming concrete from being used.