What is the range of slump (mm) of the concrete which is used as the mass concrete?
Correct Answer: B. 20 to 50
📚 Detailed Explanation: Slump for Mass Concrete
Why B (20–50 mm) is correct: Mass concrete has three characteristics that allow and prefer low slump:
1. Large volume: vibrators can access all parts easily even with stiff mixes.
2. Light/no reinforcement: no rebar congestion to navigate.
3. Heat management: low cement content and low w/c reduce heat of hydration, preventing thermal cracking.
Options C (50–75) and D (75–110) are medium-high slumps for reinforced members. Option A (10–15 mm) is extremely dry and difficult even for mass concrete.
1. Large volume: vibrators can access all parts easily even with stiff mixes.
2. Light/no reinforcement: no rebar congestion to navigate.
3. Heat management: low cement content and low w/c reduce heat of hydration, preventing thermal cracking.
Options C (50–75) and D (75–110) are medium-high slumps for reinforced members. Option A (10–15 mm) is extremely dry and difficult even for mass concrete.
Slump by Concrete Type
| Concrete Type | Slump (mm) |
|---|---|
| Mass concrete (dams, foundations) | 20–50 |
| Pavements | 25–75 |
| Normal RCC (beams, slabs, columns) | 50–100 |
| Heavily reinforced / Pumped | 75–150 |
- Mass concrete = low slump (20–50 mm) to minimise heat of hydration and maximise strength.
- IS 456 and IS 457 (mass concrete) specify this low workability range.