Dowels work by spanning the gap across a joint between
two panels. They ensure that the two panels remain level with each other at the
surface. With the addition of a plastic dowel sleeve, which encloses half of
the dowel in one of the panels, the dowel becomes debonded to one of the
panels, allowing the slabs to move horizontally in relation to each other.
There are two main types of dowel used today; bar dowels and
plate dowels. Plate dowels are more commonly used in new construction and bar
dowels are more commonly installed in existing slabs.
For the construction of formed free-movement joints:
sleeves are cast into the edge of the first panel to be cast.
the first panel has set, the dowel is inserted into the dowel sleeve and
second panel is cast around it.
The sleeve ensures that the dowel is debonded from the
other panel so that there is no restraint to the free-movement joint in the
horizontal direction. For the debonding
sleeve to work as designed, it must have the capacity for a minimum 10mm of
lateral movement in each direction.
In armoured joints, the dowel plate is welded to the
joint armour. A dowel sleeve is placed on the dowel on one side, and then both
panels can be cast either side of the armoured joint.
If a dowel’s load
transfer capacity is exceeded, it is possible that it could burst out of the
slab. This is more likely to happen if honeycombing has occurred below the
dowel or the dowel is placed too high or too low in the slab section. The shear
enhancement of fibre reinforcement is assumed to provide no resistance to this
mode of failure.