mally stopped approximately 125 mm from the edge of a slab, 100 mm from a
longitudinal joint and 300 mm from any transverse joint.
Tr ansverse lapping of reinforcement within a pavement slab will normally be
in the order of 300 mm.7.7.4 Construction of concrete road surfacings
There are a number of key issues that must be addressed in order to properly
construct a concrete pavement. These include the positioning of the reinforce-
ment in the concrete, the correct forming of both joints and slabs and the chosen
method of construction, be it mechanised or manual.
Concrete paving is a dynamic and vigorous process, so it is imperative that
the steel reinforcement is kept firmly in place throughout. In particular, chairs
made from bent reinforcing bars permit the mesh or fabric reinforcement at the
top of the slab to be secured throughout the concreting process. These chairs
should be strong enough to take the weight of workers required to walk over
them during the concreting process. Crack inducers must also be firmly con-
nected to the subbase.
Dowel bars used in expansion and contraction joints are usually positioned
on metal cradles so that they will not move from their required position while
the concrete is being placed and compacted. These cradles, however, should not
extend across the line of the joint. Tie-bars in warping joints are also normally
part of a rigid construction that allows them to be firmly secured to the sup-
porting subbase, while those in construction joints can be inserted into the side
of the pavement slab and recompacted. Alternatively, both dowels and tie-bars
can be vibrated into position.
Where the top of the pavement foundation consists of unbound material, it
is possible that grout from the concreting process may leak into it. To prevent
this occurring, and to minimise frictional forces, a heavy-duty polythene sepa-
ration membrane is positioned between the foundation and the jointed concrete
pavement.
The pavement slab can be constructed in one or two layers. Two layers could
be employed where an air-entrained upper layer is being installed or for ease in
the placement of reinforcement, where the reinforcement could be placed on the
lower layer after it has been compacted, thereby obviating the need for sup-
porting chairs.
On large pavement construction projects, continuous concreting is the most
economic method of placement. Within it, the paver moves past joint positions,
requiring that crack inducers, dowels and tie-bars be kept in position by methods
referred to above. Purpose-built highway formwork is typically made of steel,
held in position by road pins driven through flanges in the form and into the
pavement foundation immediately below. Once the steel reinforcement and the
formwork are in place, the concreting can commence.224 Highway Engineering