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Paving Principles and Control Methods
How a Screed Works
9
P-32+ and P-32 Operator’s Manual P/ N: 1001547-01
The P force remains constant if the paver is kept moving at a consistent speed at all times. If the paver is
allowed to stop, the screed settles in the fresh mat and leaves a mark. The mark cannot be fully smoothed out
by the roller and a bump ends up in the mat that shows up in the profilograph readings. Changing the speed
of the paver also causes the screed to rise and fall, affecting mat thickness.
The optimum paving speed is determined by the depth and width being paved and the rate at which material
can be delivered to the job. Calculate the tons/hour into feet per minute (Figure 18). Do not start and stop the
paver.
Figure 18: Travel Speed to Reduce Tow Point Force ( “P”)
Truck Exchange, Another Tow Point Force
It is very important that truck exchanges be carried out as smoothly as possible to avoid disturbing the smooth,
uninterrupted forward motion of the paver. The following lists some steps to take to avoid disturbance of the
paving operation by trucks.
1. Stop the mix delivery truck close, but not too short of the paver. Always allow the paver to pickup trucks on
the run.
2. Never allow the truck to bump the paver. Allowing trucks to bump the paver when backing up, can drive
the screed into the mat and produces bumps and ridges which may not roll out.
3. Trucks applying and holding their brakes excessively while dumping their load may cause the paver to
slow, which in turn causes the screed to rise. The truck driver should apply only light pressure on the
brakes, sufficient to maintain contact with the paver.
4. Dumping of material in front of the paver as the truck pulls away after emptying its load into the hopper,
can cause the paver to ride over the pile of material with subsequent adverse effects on mat quality.
Avoid trucks pulling away prior to completely dumping all material. Use a dump person to monitor and
regulate truck movements in front of the paver.
Head of Material (M)
One of the primary functions of the paver tractor is to convey and distribute paving material onto the ground in
front of the entire width of the screed. This material, once deposited in front of the screed is the head of material
over which the screed passes.
One of the keys to smooth paving is to maintain this head of material as constant as is possible. The resistance
to forward motion exerted by the head of material (M) is one of the major component of resistance to forward
motion (Figure 19). Control of this force is a basic and necessary function of any paving operation.
Figure 19: Head of Material Force ( M)
The volume and consistency of the head of material determines how much paving material flows under the
screed and influences mat thickness and surface texture.
Head of
Material
(Force M)
M
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