hydraulic system for the truck-bed hoist should be
frequently inspected to guard against hydraulic fluid
leakage. Such leakage on the roadway surface will
prevent good bonding between the roadway and the new
mat. When enough oil is spilled that the mix can absorb
it, the mix can become unstable at that spot. For this
reason, leaking trucks should not be used.
Tarpaulins should be pulled over the mixture during
hauling in cool weather or on long hauls to protect the
mixture from excessive cooling. A cool mix forms lumps
and a crust over its surface. When a tarpaulin is used, care
must be taken to be sure it is securely fastened to the top
of the truck bed so that cold air cannot funnel under it.
During delivery, the driver must direct the truck
squarely against the paver and should stop the truck a few
inches from the paver before the truck tires make contact
with the paver roller bar. Backing the truck against the
paver can force the screed back into the mat, leaving a
bump in the pavement even after the mat is rolled.
The truck bed must be raised slowly. When the mix
is dumped too rapidly, segregations occur, because the
coarser aggregates will roll down the sides of the load.
BOTTOM-DUMP TRUCKS. Bottom-dump
trucks can be used when a grader is spreading the mix
or when a pickup device is used to feed the windrow left
by the truck into the paver hopper.
Two common methods for unloading bottom-dump
trucks are in use. The first method involves the use of
a spreader box, designed to be operated under the gates
of the truck. The amount of material, placed in the
windrow, is governed by the width of the spreader box
opening. The disadvantage of this method is that the
spreader box can restrict the amount of material to less
than the required amount. The second method, which is
used more often than the first, is to use chains to control
the dump gate opening.
NOTE: Automatic devices are also available for
controlling gate openings.
Variations in the size of the windrow, deposited by
the bottom-dump truck for pickup by the paver, and
irregularities in the surface on which the material is to
be placed will cause variations in the amount of material
fed to the paver hopper. This often causes variations in
the finished surface. It is, therefore, essential that the
windrow, deposited by the truck be as uniform as
When the windrow is deficient in size,
material can be added to it to keep the paver from
starving. When the windrow contains too much mix, a
short gap in depositing with the next truck will
compensate for the excess. The windrow length must
also be controlled particularly in cool weather.
Windrowed material will cool below spreading and
compaction temperatures in cool weather, particularly
when delay occurs because of paver malfunction. The
limit of the windrow should be no more than one truck
load ahead of the pickup machine to prevent excessive
cooling of the mix in cold weather.
When the loader and paver are directly coupled,
vibration of the pickup device maybe transmitted into the
paver, causing ripples and roughness in the mat surface.
These vibrations generally result from worn and defective
parts or from improper mounting or adjustment.
The purpose of a truck hitch on the front of the paver
hopper is to keep the truck dumping hot mix into the
hopper in contact with the paver. If, during dumping,
the truck and the paver separate and hot mix spills, it
must be cleaned up before the paver passes over it.
Two types of truck hitches are in common use. One
type uses an extension that reaches under the truck and
hooks onto the rear axle of the truck. The other type of
hitch has retractable rollers that are attached to the truck
push bar and grip the outer side of the rear wheels of the
truck. The rollers revolve with the wheels while the
truck dumps its load into the hopper.
Pivoted Truck Push Rollers
The pivoted push roller is a device, mounted on the
front of the paver, that adjusts when alignment between the
truck and paver is uneven. This device reduces the uneven
force exerted on the paver by the misaligned truck,
minimizing interference in the steering of both vehicles.
ASPHALT FINISHERS (PAVERS)
Various makes and models of asphalt finishers are
used by the Naval Construction Force (NCF). Two
types are shown in figure 16-38. Even though the
finishers may operate differently, their primary jobs are
all the same: receiving asphalt and spreading it in a
predetermined, uniform length, width, thickness, and
shape. The finisher also provides initial compaction of
the mat (layer of mixture in place.)
Because asphalt finishers are different, you must
always read the operators manual for the unit you are
operating. It is also good to have a practice sand
laydown before actually using a hot mix. This is to
familiarize yourself and others with the machine and
also ensure that the machine is working properly. Figure
16-39 shows a practice laydown, using just the
aggregate mix without the asphalt.