Mechanised paving allows a higher quality concrete finish to be attained. The
spreading, compacting and finishing of the pavement involves use of a fixed-
form or slip-form paving train.
Fixed-form paving uses steel forms or a preconstructed concrete edge-beam
to retain the concrete, using machine rails to support and guide the individual
items of plant utilised in the pavement construction process. A train of machines,
each individually operated, run along the rails, executing the basic tasks of:
Spreading the concrete
Compacting it by vibration
Finishing the surface.
Machines for dowel and joint forming that leave the surface of the concrete with
the required texture and the addition of curing compounds may also be included
within the process. The machines themselves may be manually propelled, self-
powered or towed along the rail.
Typical types of machinery used in a fixed-form paving train are:
(1) Feeder – receives concrete as it arrives at the required location
(2) Spreader – distributes the concrete across the full width of the pour in ques-
tion, discharging it at a controlled rate
(3) Rotary strike-off paddles and compaction beams – regulate the concrete
by trimming any irregularities in the concrete and vibrate its surface
(4) Dowel/tie-bar placers – place these elements in the appropriate joints either
manually or by vibration
(5) Joint groove formers and finishers – grooves formed by a knife travelling
within the plastic concrete (wet-formed). Otherwise, a vibrating blade can
be used to form them when the concrete has hardened sufficiently
(6) Final finishing equipment – additional compaction and regulation of the
concrete after the dowel and tie-bars have been put in place. (Machine uses
two oblique finishing beams oscillating in opposite directions to achieve a
uniform finish to the surface of the concrete)
(7) Curing compound sprayer
(8) Protective tentage.
The sequence of operations for two-layer placement with a fixed-form paver is
illustrated in Fig. 7.19.
The previous method is analogous to manually placing the concrete. The
process can also be completed without using fixed-forms. This process is called
slip-form paving. It works on the basis that the sides of the pavement slab will
support themselves before an initial set has been developed within the concrete.
It produces a fully compacted slab. It cannot therefore be subsequently disturbed
in order to place dowel or tie-bars, as the surrounding concrete could not then
be properly made good. The slip-form paver spreads, compacts and finishes the
concrete with only the forming and finishing of the joint grooves, texturing and
curing done using other pieces of equipment.
Highway Pavement Materials and Design 225