Paving Principles and Control Methods
How a Screed Works
P-32+ and P-32 Operator’s Manual P/ N: 1001547-01
“Center Streak” segregation is also caused by feeder gates being set to tow. Adjust as necessary to provide
sufficient uniform material at the center of the paver.
Mix Temperature Characteristics
A common paving problem is inconsistent temperatures in the asphalt mix. As the material cools it loses its
viscosity making it more difficult to compact. If the resistance to compaction increases, the screed naturally
increases its angle of attack and begin to float up. This changes the mat depth, resulting in bumps in the surface.
If the mix and or screed temperature are too low, the screed may no longer slide smoothly over the material
and a tearing of the mat occurs.
Simple steps to take to control temperature variations:
1. Ensure that haul trucks take the shortest, most practical route to the paver. Make certain that all trucks
take the same route to the paver.
2. Make sure that the trucks arrive at the same order in which they were loaded at the asphalt plant.
3. Ensure that no bunching of trucks occurs at the paver, with several trucks waiting to dump their loads.
4. Match lay-down rate to material delivery rate.
Weight of Screed (W)
For the weight of screed force (W) to remain constant, the weight of the screed, or the downward pressure
exerted by the screed on the paving material, should not change (Figure 22). The weight of the screed is
measured in pounds per square inch.
Figure 22: Weight of Screed
Mem bers of t he paving crew clim bing on and off t he screed also have som e af f ect on the w eight of screed f orce.
“Center Streak” segregation can be limited and even eliminated by slowing paving speed.
Temperature problems may occur before the time the material is loaded into the trucks, or during the
trip to the paver. They can be the result of temperature variations at the plant. If this is not
addressed prior to delivery of material to the paver, waviness in the mat results.
Weight of Screed (W)