In expansion joints of cement concrete pavements, loads are transferred from one slab to the next through:
Correct Answer: B. Dowel bars
📚 Detailed Explanation: Dowel Bars Transfer Load Across Expansion Joints
Why B (Dowel bars) is correct: In cement concrete pavements, expansion joints create a complete gap in the slab — no aggregate interlock, no reinforcement continuity. Yet wheel loads crossing the joint must still be transferred from one slab to the next to prevent differential vertical movement (faulting). This is achieved by dowel bars: smooth, round steel bars (typically φ25–32 mm, spaced 300 mm c/c) placed perpendicular to the joint, half-bonded in each slab, with one end coated or sleeved to allow longitudinal sliding.
Types of Load Transfer Devices in Pavements
| Device | Joint Type | Function | Bond Condition |
|---|---|---|---|
| Dowel Bars (φ25–32 mm, smooth) | Expansion & Construction joints | Vertical load transfer; allows horizontal movement | Bonded in one slab, free (sleeved/greased) in the other |
| Tie Bars (φ12–16 mm, deformed) | Longitudinal joints | Keep adjacent slabs at same level; prevent lane separation | Bonded both sides; does NOT allow relative movement |
| Aggregate Interlock | Contraction / dummy joints | Passive load transfer via interlocking rough crack faces | No steel; relies on crack face texture |
| Longitudinal bars | Continuous reinforced pavements | Control crack width; not used at expansion joints | Fully bonded; crosses contraction joints only |
Dowel Bar Specifications (IRC:15)
| Parameter | Specification |
|---|---|
| Diameter | 25 mm for slab thickness 200–250 mm; 32 mm for 300 mm slabs |
| Length | Typically 450–500 mm (half in each slab) |
| Spacing (transverse) | 300 mm centre to centre |
| Material | Mild steel (smooth surface for sliding) |
| Free end | Coated with bituminous paint or inserted in PVC sleeve; cap at end to allow slab expansion |
| Alignment | Must be exactly parallel to the road axis; misalignment causes locking and joint failure |
- Dowel bars transfer vertical loads across expansion joints while permitting horizontal (thermal) movement.
- One end is bonded (anchored); the other end is free to slide (greased/sleeved) to allow expansion/contraction.
- Tie bars are used at longitudinal joints to prevent lane separation — not for load transfer or movement accommodation.