ing edge of the screed is not in contact with the mat
being laid.
Vibrators connected to the screed bottom support
will not be operating efficiently as the full screed plate
width is not being utilized. Mat appearance and
texture will change with only slight movement of the
screed adjusting hand wheels.
f. Loose or worn screed.
7. Correct pull point settings become a matter of
experience. Locating center line of pull points 14 1/4"
from the ground has proven satisfactory for most
paving jobs. Settings listed will normally cover the
necessary adjustments when laying both stable and
unstable mixes. The softer and more unstable the
material, the more important it becomes to have the
screed flat with the mat.
NOTE: Unstable mixes can be caused
by too much asphalt in the mix, poor
poor
quality
asphalt,
excessive temperature, moisture in the
material and insufficient dust.
IMPORTANT: Both pull points must be
located equal distance from the ground.
Effect of Pull-point Height on Screed Wear
Figure 21
erational difficulties will be encountered.
a. Premature wear on the trailing edge of the the
screed.
b. A tendency for the screed to climb each time the
paver starts with normal hand wheel setting. Poor
control of mat thickness will exist and good transverse
joints will be difficult' to make.
c. Possible tearing of the mat because of excessive
ironing effect of the screed.
d. Loose or worn screed.
6. When the pull points are too high and the front of
the screed is tilted down, in order to maintain the
correct mat thickness, the following wear and
operational difficulties will be encountered.
a. Premature wear on the leading edge of screed and
Flat Strike-off Installed on Screed
possibly deformation of the strike-offs because of the
Figure 22
excessive pressures exerted against it when operating
in this manner.
STRIKE-OFF
b. Bumpy, wavy road caused by the screed riding on
The strike-off located ahead of the screed plate, is
its leading edge.
a metering, pre-compactor, and pre-screeding device,
c. Tendency for screed to dip each time the paver
that when properly positioned provides the exact
starts with normal hand wheel setting.
amount of material to the screed. It also absorbs wear
d. Tearing the mat, caused by the "digging in" action
which would otherwise take place on the leading edge
of screed.
of the screed bottom. If this strike-off is not properly
e. Loss of compaction will result as the trail-
adjusted and maintained, it can cause operational
difficulties.
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