What Are Dowel Bars?
Dowel bars are short steel bars that are installed in concrete slabs to provide a mechanical connection that doesn’t restrict horizontal joint movement. They are designed to reduce joint deflection and stress in the approach and leave slab by increasing load transfer efficiency. Typically, dowel bars are used in concrete pavements.
Dowel Bar Placement
Dowel bars are placed at the traverse joints of concrete pavement and must always be parallel to the centerline. Half of the bar is embedded in one of the concrete slabs and the remaining half is bonded in the adjacent slab. Dowel bars are usually inserted at mid-slab depth and coated with a bond-breaking substance to prevent bonding to the PCC.
Dowel Bars And Tie Bars
On the face of it dowel bars and tie bars can appear very similar but they play different roles in concrete reinforcement. They both significantly improve performance of pavement joints and reduce life cycle cost. Tie bars, however, are deformed rebars that are designed to hold faces of rigid slabs in contact to maintain aggregate interlock. Significantly, tie bars are not used as load transferring devices.
Dowel bars are placed across traverse joints, whereas tie bars are installed across longitudinal joints. Dowel bars transfer load from one slab to another and tie bars prevent lanes from separation and differential deflection. Dowel bars are commonly round, smooth, epoxy-coated steel bars and tie bars are deformed epoxy-coated steel. Dowel bars reduce joint faults and corner cracking and tie bars reduce traverse cracking.
Dowel Bar Concrete Accessories
There are a number of concrete accessories specifically designed for use with dowel bars. For instance, expansion dowel bar caps are rigid PVC tubes with a compressible plug one end, designed as a tight fit over the dowel bars in expansion joints. Dowel bar cradles are used to support dowel bars in expansion and contraction joints of road and floor slab construction. To prevent concrete bonding on the dowel bar a dowel bar sleeve is installed.
Dowel bars Specification
Dowel bars are usually 32 to 38mm (1.25 to 1.5 inches) in diameter, 460mm (18 inches) in length and spaced 305mm (12 inches) apart. Dowel bars can be supplied in strength grades 200, 500 and 600 as specified in BS 6744:2016. This European standard specifies the requirements and test methods for solid stainless steel bars used for reinforcing concrete.
The Alternatives To Dowel Bars
Ancon’s DSD range of connectors are a two-part assembly that offers some advantages over plain dowel bars. No drilling of formwork or concrete is required which means installation is fast and accurate. No additional protection is required as they are manufactured from corrosion resistant stainless steel.
With low frictional resistance and good abrasion resistance the Schöck Dorn type SLD (heavy duty dowel) ensures joint permanency and maintenance-free movement, thus sustaining load bearing capacity. The dowel transmits the loads from one structural component through bending in the sleeve and thus into the other structural component. Schöck dorn shear dowels are cost effective with the highest level of reliability.
The Advantages Of Dowel Bars
The main advantage of dowel bars is to transfer load without restricting horizontal joint movements that arise from temperature, as well as moisture expansion and contraction in the concrete slabs. Dowel bars also help regulate the vertical and horizontal alignment of the slabs.
Author Lydia Swallow. Category Concrete Reinforcement. First published Fri, 11 Jun 2021 12:00:00 +0100