What is the interval at which expansion and contraction joints are provided for a smooth foundation interface laid in winter in India?

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 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.