contains slightly less material than the immediately
adjacent area. After rolling, you can see that an area
shows up as a transverse ripple in the pavement. A
power lag can also interfere with the smooth and
consistent operation of the electronic screed controls.
HOPPERS, FLOW GATES, AND AUGERS.
The hopper, the slats on the feed conveyor, the flow
gates, and the augers should be checked for excessive
wear and observed to be certain they are operating
properly. Necessary adjustments should be made to
ensure that these components are functioning as
designed and are able to deliver a smooth flow of
mixture from the hopper to the roadway. This includes
adjustments to any automatic feed controls.
The speed of the conveyor and the opening of the
control gates at the back of the hopper should be
adjusted, so just enough mixture is being delivered to
Figure 16-41.-Tamping bar.
the augers to keep the augers operating about 85 percent
of the time.This allows a uniform quantity of mix to be
maintained in front of the screed.When additional mix
is required to allow an increase in the thickness being
placed, the flow control gates should be adjusted.
Augers should be kept about three-quarters full of
mixture during paver operations.
In operation, the screed is pulled along behind the
tractor unit. The long screed pull-arms are pivoted that
permits the screed to have a floating action, as it travels
along the road. As the tractor unit pulls the screed into
the mix, the screed seeks the level that allows the path
of the screed to be parallel to the direction of pull. At
this level, all of the forces, acting on the screed, are in
balance, as the paver moves down the road. The screed
plate irons the surface of the mixture, leaving the mat
thickness at a depth that conforms with job specification.
Mat thickness and crown shape are regulated by screed
Tamping bars (fig. 16-41) or vibratory
attachments then compact the mat slightly in preparation
for rolling. Figure 16-42 shows the workings of a
Attaining proper mat thickness is a matter of
balancing the forces, as shown in figure 16-42, with one
1. To maintain forward motion of the screed, force
P must be greater than force H.
2. To increase the thickness of the mat, tilt the
screed plate so that more material is crowded under the
The screed will rise until the finished
surface is again in a plane parallel to the direction of pull.
Figure 16-42.-Forces acting on the screed.