Concrete Mix Design MCQ with answer and solution

Concept

Slump test selection for reinforced columns

Formula

NONE

Step-by-step solution

1. Structural columns in modern high rise buildings feature dense longitudinal rebar cages and tight confinement ties. 2. The concrete mix requires medium to high workability (slump 100 to 150 mm) to flow through congested rebar without segregating. 3. The slump test is the most direct, practical, and universally standardized field test to measure medium to high workability of flowing concrete. 4. Hence, the slump test is the most suitable method for testing column concrete mixes. Answer: A

Explanation

Columns in multi-story high rise structures have densely packed vertical rebars and tight lateral ties, requiring concrete that flows freely around reinforcement without segregation. The standard slump cone test is the most appropriate field method to verify that the mix achieves the required medium to high workability (typically 100 to 150 mm slump) for pumpability and self-consolidation.

Why the other options are wrong

B) Vee-Bee consistometer is designed for very dry, zero-slump mixes and fails for medium-to-high workability column concrete. C) Compaction factor test is sensitive for low to medium workability but less convenient on site than the standard slump cone. D) Flow table test is primarily used for high-fluidity mortar or self-consolidating concrete rather than normal structural column mixes.

Shortcut

Medium to high workability (congested rebar/columns) = Slump test; Stiff/dry mixes = Vee-Bee test.

Common mistake

Recommending Vee-Bee consistometer for a high-workability column mix, which is only suitable for dry stiff mixes.