MCQs on Workability of Concrete — Page 2
Questions 16–30 — Tap an option to check your answer.
Q16: What is the slump of pumped concrete used in heavily reinforced section if the degree of workability is medium as per IS 456-2000?
Difficulty: Medium
Solution:
For pumped concrete in heavily reinforced sections, IS 456:2000 specifies medium workability with slump 50-100 mm. Pumped concrete generally requires higher slump than hand-placed concrete for the same application.
Q17: Compaction factor for heavily reinforced section with vibration is ………….
Difficulty: Medium
Solution:
A compaction factor of > 0.92 (high workability) is required for heavily reinforced sections even when vibration is used, because the concrete must flow readily through congested reinforcement before vibration helps consolidate it.
Q18: Higher workability of a concrete is required if the structure is
Difficulty: Easy
Solution:
Thin sections that are also heavily reinforced require the highest workability because: (1) thin cross-sections limit vibration effectiveness; (2) heavy reinforcement creates congestion; (3) the combination means concrete must flow freely into every corner without voids.
Q19: Workability of concrete mix with low water cement ratio is determined by:
Difficulty: Medium
Solution:
The compaction factor test is used for low-workability (stiff) mixes because the slump test is insensitive for such mixes — a stiff mix shows zero slump even at different workability levels. The compaction factor test can distinguish between different levels of low workability.
Q20: What is the bottom diameter (mm) of the standard mould used in slump test of the concrete?
Difficulty: Easy
Solution:
The bottom diameter of the standard slump cone (IS 1199) is 200 mm (20 cm). The full dimensions are: top diameter = 100 mm, bottom diameter = 200 mm, height = 300 mm.
Q21: The figure given below represents a:
Difficulty: Medium
Solution:
When the concrete completely collapses and spreads outward after removing the mould, it is called a collapse slump. This indicates a very wet, highly workable mix with excessive water content.
Q22: The result of Vee-Bee test is expressed in terms of ……………
Difficulty: Easy
Solution:
The Vee-Bee test result is expressed in seconds (s). It measures the time taken for the concrete to completely remould from its slumped shape to fill the cylindrical container when vibrated on a vibrating table.
Q23: Which of the following statements is true?
Difficulty: Easy
Solution:
Workability reduces with time after mixing because cement begins to hydrate, absorbing water and stiffening the paste. Additionally, aggregates may absorb some of the free water, and evaporation reduces water content. All of these progressively reduce workability.
Q24: If the slump of a concrete mix is 60 mm, its workability is:
Difficulty: Easy
Solution:
A slump of 60 mm falls in the range of 50-100 mm which corresponds to medium workability per IS classification. This is suitable for normal reinforced concrete elements like slabs, beams, and columns.
Q25: Pick up the incorrect statement from the following:
Difficulty: Medium
Solution:
The slump cone mould is a frustum of a RIGHT CIRCULAR CONE, not a hexagonal pyramid. It is circular in cross-section at both top and bottom. The other three statements are all correct descriptions of the mould.
Q26: A slump of 50-100mm can be used for:
Difficulty: Easy
Solution:
A slump of 50-100 mm (medium workability) is used for structural members like beams, columns, slabs, and walls. Mass concreting uses low slump (25-75 mm); strip footings and trench fills use low to very low slump.
Q27: Which admixture is used to improve workability of concrete?
Difficulty: Easy
Solution:
Plasticizers (also called water reducers) improve workability by dispersing cement particles and reducing inter-particle friction. They allow a reduction in water content (and hence w/c ratio) while maintaining or improving workability.
Q28: Compacting factor is defined as the ratio of –
Difficulty: Easy
Solution:
The Compacting Factor (CF) = weight of partially compacted concrete / weight of fully compacted concrete. As workability increases, partially compacted concrete approaches fully compacted concrete, so CF approaches 1.0.
Q29: Which of the following is CORRECT for the workability of the concrete having the compaction factor of 0.92?
Difficulty: Easy
Solution:
A compaction factor of 0.92 corresponds to medium workability in the IS classification. The range for medium workability is CF 0.85-0.92, so CF = 0.92 is at the upper end of medium (just below high workability).
Q30: For given workability the grade requiring the least amount of water is one that gives
Difficulty: Medium
Solution:
For a given workability (target slump), the aggregate grading that requires the least water is the one that minimizes total surface area. Less surface area means less water needed to wet and coat all particle surfaces, leaving more free water for lubrication — achieving the same workability at lower water content.