Edges Loose - Decrease Front Crown
Center Loose - Add More Front
Crown
Effect of Crown on Mat Uniformity
Figure 5
add front crown by turning the nut 1/6th turn at a time until the mat has the desired appearance. Adjustment
should be made slowly, waiting each time for the effects of the new setting.
Tight mat edges and a marking or looseness at the center of the mat indicates a need for more front crown.
Add crown to the front edge of the screed 1/6-th turn of the adjusting nut at a time, waiting each time for the
effects of the new setting, until the mat has the desired appearance.
The rear crown adjustment should not be changed unless a new or different degree of crown is desired in
the finished mat. Front crown adjustment does not affect the road crown, it only helps to get proper distribution
of material under the screed. The front crown must always be adjusted after the rear crown adjustment is
correct.
The initial crown settings are 1/16 to 1/8" more in the front crown than in the rear crown. For example: The
rear crown setting is for 1/4" crown in the road, therefore the front crown would be 1/16"more or 5/16" total.
Final adjustment must be made when the paver is actually laying mat. This eliminates the possibility of
crown error and enables the operator to observe the quality of the surface. If the density and texture are not
uniform, adjustment of the lead crown differential should be made to determine whether the mat can be
improved by this simple change in screed attitude.
Matching Mats
In any paving operation where two or more mats are joined together, this procedure is called matching a
joint (Figure 6). The joint may be either parallel or transverse, depending upon the phase of operation. When
matching any joint the operator should always have sufficient thickness so when the mat is rolled it will be the
same depth as adjoining mat. Extra thickness depends upon how thick a mat is being laid. Example: a 4" black
base mat may require 5" of fresh material in order to measure 4" after final rolling. A 12" mat may require
only 13,14" of material.
(1) Parallel Joints-The "CEDARAPIDS" Bituminous Paver is designed to match one mat to another mat by
overlapping the previously laid mat. The amount of overlay will depend some upon skill of the operator. (Refer
to Figure 6.) The operator should also consider the following examples when laying mats with parallel joints.
(a) Match the mats when possible before the asphalt sets up. If it is possible to do this, the roller should
be kept away from the first mat approximately 6" to 1'.
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