(2) When resurfacing, specifications may call for a mat too thin to cover the high spots, thus the screed will
drag. The operator should watch for such high spots and have them bladed down be- fore paving. Extreme
trouble will be experienced if large stone has been used in the material. This is an important reason why the
mat should be at least 1 1/2 times the largest stone size.
(3) When laying a binder course on a base with holes, best results will be obtained by filling these holes
with binder ahead of the paver.
(4) Screed should be adjusted to follow the contour of intersections when laying city pavements. More
material may be required to obtain this contour.
(5) Never cover catch basins. Always decrease mat thickness if basins are lower at intersections, to give
proper slope for collecting water. When paver travels care should be taken not to hook the screed on any rigid
object which could damage the strike-off plate or other parts of the assembly.
(6) When changing to faster speeds the screed operator should make any adjustments necessary to
maintain proper mat thickness.
(7) When resurfacing city streets, the operator should watch for manholes.
(a) Mark the pavement at one side of the manhole so it can be uncovered after paver passes.
(b) When necessary, the screed thickness control should be changed to allow more material to cover
manhole.
(c) If crawler is in line with manhole, adjust thickness control to correct the rising of paver.
(d) If manhole is more than an inch high, a few shovels full of material will enable the crawler to climb
over it.
(e) When material covers manhole, it should be cleaned off before roller passes over it.
Mat Conditions
There are various conditions that will affect the finished mat or surface. These conditions are usually an
indication of improper adjustment, operation, temperature, crown or material. When these conditions are
evident, they can be eliminated by proper corrections made by the operator.
(1) Proper Crown Adjustment - The leading edge or front of the screed should be set with a crown of at
least 1/16" more than the trailing edge or rear of the screed. When making final adjustment on mat, do not turn
the hex nut more than of a turn at a time. Observe results and make further correction if needed.
(a) If the mat is loose or coarse in the center and the edges are firm, there is not enough crown on the
leading edge of the screed.
(b) If a sandy line is present in the center of the mat and the edges are loose, this indicates too much
crown on the leading edge of the screed. It can also be due to an incorrect strike-off plate adjustment.
(2) Voids in Mat - When any form of holes show up across the mat surface, these may be due to any of the
following:
(a) Material in the form of lumps that are rich in asphalt will not break up and pass under the screed.
This starves the mat.
(b) Any foreign object in the material that will not pass under the screed also starves the mat.
(c)Material partially set up due to long hauls is the most common cause of tearing. A mix that is short of
solvents also acts the same as a cold load.
NOTE: To correct this type of tearing to the
mat surface, first try to remove the cause.
When it is impossible to hold the heat in the
material due to long hauls, a higher plant
mixing temperature should be used. Also,
covering loads and insulating truck bodies will
help hold the heat. Adding heat to the screed
helps to smooth out the mat, because material
will not stick to a hot screed.
(3) Tearing of Mat Surface - This tear looks like some object has been dragging or scuffing the surface.
This is caused by material sticking to the screed and building up. Heat to the screed will generally take care of
this condition. If this condition is not cleared up by heating the screed, the screed should be raised and cleaned.
Asphalt containing excess moisture will not lay properly.
(a) If tears appear along the edges of the mat, there is too much material being forced out against the
end plate. Adjust gates and automatic feed control to cut down the amount of material in front of the screed.
(b) If the screed surface is rough, or rusty, this condition will also cause tearing. to the mat surface.
Also swab or spray screed plate at end of each day's operation.
(c) When mix gradation is low in small sizes of aggregates, the mix will cause an open- type surface
texture. When this is not desirable in the mix, a sufficient amount of smaller aggregate sizes should be added.
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