What Is Dowel Bar – Its Purpose, Use And Advantages
What Is Dowel Bar?
Dowel bar is short round, smooth steel rod used to provide a mechanical connection between slab without restricting horizontal joint movement. These bars are mainly used in jointed plain concrete pavement (JPCP) to carry the additional stress and load induced due to the moving vehicle.
Dowel bars are used
1. To transfer the load from one slab to its adjacent slab such that two consecutive slabs move together and reduce impact loading developed by the slabs by their independent movement.
2. To reduce joint faulting and corner cracking.
3. To improve the performance of pavement joints.
The size of dowel bars depends on the thickness of the pavement. Usually, these bars are 18 inches (460mm) long, 1.25 to 1.5 inch (32 to 38 mm) in diameter, and spaced 12 inches (305mm) apart. To protect the rods from corrosion they are either stainless steel or epoxy coated.
Dowel bars are placed across transverse joints of concrete pavement to allow movements. They are inserted at the mid-depth of slab and coated a bond breaking material to restrict bonding to the PCC. Thus dowels help to transfer loads allowing expansion and contraction of adjacent slabs independently.
Dowels must be placed parallel to the centerline. New channels must be cut so that at least one-half dowel can be on each side of the joint or crack.
Advantages Of Dowel Bars:
1. reduces deflection and stresses.
2. It increases the load-carrying capacity of slabs.
3. It increases the initial pavement life.
1. Dowel Baskets.
2. Dowel bar inserter (DBI).
A bond breaker (usually grease) must be applied prior to placement.
1. Bars are missing or misplaced due to poorly adjusted equipment, damaged dowel baskets, or improper basket anchoring.
2. Concrete around the bars is poorly compacted or too stiff mix is used.
Dowel bars are also used in RCC wall for slabs and columns. They are placed in two ways:
Method 1: Short length bar placed before pouring concrete in position. It is the most common and successful method in terms of bonding, cost-effective as it doesn’t require chemical for bonding purposes.
Method 2: Drilling hole in concrete, and putting Hilti chemical for strong bonding. It is expensive as Hilti chemical is used which is costly. This method is adopted when we forgot to place extension bars before concreting.