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Paving Principles and Control Methods
How a Screed Works
13
P-32+ and P-32 Operator’s Manual P/ N: 1001547-01
The primary factor affecting this force is changing the width of the screed (Figure 23). Extendible screeds weigh
the same whether they are fully retracted or fully extended. The difference is the wider the extension of the
screed the greater the surface area of paving material to support. An extended screed has fewer psi, which
means less compaction, causing the screed to raise.
Figure 23: Width of Screed Affects Weight of Screed
Quality of Paving Base
There are factors other than the four main forces that can have an effect on the quality of the mat. An important
one is the quality of the base to be paved. It makes more sense to build smoothness from the base up, than to
try to smooth a road in the last lift of paving. However, on overlay paving jobs, we have to work with what we
have.
Remember that a mat which appears smooth immediately behind the paver, may actually contain areas of
considerably varying thickness of material as a result of undulations in the base being paved. Due to the
principle of “Differential Compaction” high spots do not compact as much as the low, therefore allowing some
of the irregularities to be rolled back onto the mat (Figure 24). To minimize this problem, lay a leveling course
in the low spots or pave multiple lifts to average out the irregularities.
Figure 24: Differential Compaction
Rolling Techniques
A well laid mat can end up with a poor ride quality if proper rolling methods are not followed. Consult your
compaction equipment manufacturer's manuals and handbooks on compaction techniques.
Controlling Mat Quality
The primary purpose of the asphalt paver is to place a smooth mat of material. The primary function of your
Topcon P-32+ or P-32 System is to control the vertical position of the screed in relation to the surface being
paved. Automatic grade and slope control systems can help tremendously in controlling mat smoothness but
mat quality is also dependent on the following factors:
Mat Before Rolling
Mat Before Rolling
Mat After Rolling
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