What is the interval at which expansion and contraction joints are provided for a smooth foundation interface laid in winter in India?
Correct Answer: B. 50 to 60 metres
📚 Detailed Explanation: Expansion/Contraction Joints at 50–60 m in Winter, Smooth Interface
Why B (50 to 60 metres) is correct: IRC (Indian Roads Congress) specifications for cement concrete pavements prescribe joint intervals based on season of construction and slab thickness. When concrete is laid in winter (October to March) over a smooth foundation interface (lower friction), the contraction/expansion joint spacing is 50 m for 15 cm and 20 cm slabs, and 60 m for 25 cm slabs. Hence the range is 50 to 60 metres.
Joint Spacing for CC Pavements (IRC Specifications)
| Season of Laying | Foundation Interface | Slab Thickness (cm) | Joint Interval (m) |
|---|---|---|---|
| Winter (Oct–Mar) | Smooth | 15 | 50 |
| 20 | 50 | ||
| 25 | 60 | ||
| Winter (Oct–Mar) | Rough | 15 | 40 |
| 20 | 40 | ||
| 25 | 50 | ||
| Summer (Apr–Sep) | Smooth | 15 | 90 |
| 20 | 90 | ||
| 25 | 120 | ||
| Summer (Apr–Sep) | Rough | 15 | 75 |
| 20 | 75 | ||
| 25 | 90 |
Why Season and Interface Type Affect Joint Spacing
| Factor | Effect on Spacing |
|---|---|
| Winter laying | Concrete placed at low temperature; will expand significantly in summer; joints closer to handle larger expansion range → smaller spacing |
| Summer laying | Concrete placed near maximum temperature; will contract in winter; less expansion expected → larger spacing |
| Smooth interface (polythene sheet) | Lower friction; slab can slide more freely; joints can be slightly further apart |
| Rough interface (granular sub-base) | Higher friction; slab is more restrained; joints needed closer together |
Thermal Expansion Estimate:
ΔL = α × L × ΔT
Where: α = 10 × 10&sup-;&sup6; /°C (concrete), L = slab length, ΔT = temperature rise
ΔL = α × L × ΔT
Where: α = 10 × 10&sup-;&sup6; /°C (concrete), L = slab length, ΔT = temperature rise
For L = 50 m, ΔT = 30°C:
ΔL = 10 × 10&sup-;&sup6; × 50 × 30 = 0.015 m = 15 mm
Expansion joints must accommodate this 15 mm movement.
- Smooth interface + winter laying = 50 m (15 & 20 cm slab) and 60 m (25 cm slab) → range 50–60 m.
- Summer + smooth = 90–120 m; summer + rough = 75–90 m; winter + rough = 40–50 m.
- Joint spacing accounts for concrete placed cold in winter expanding greatly in summer heat.