ASPHALT ANSWERS
paction opportunity. In addition, there
is a tender zone. Depending on the kind
of aggregate and mix properties, this
zone ranges from 240° to 190°. This is
what I call the “no go” zone, meaning
stay off the mat. During this time the
mat shoves, checks and can create that
bulge in front of the roller that we all
have seen. Once the temperature drops
below 190° you have another opportu-
nity and the mix can support again the
weight of a roller. But take note, this last
opportunity to achieve desired compac-
tion is difficult and the operator needs
to watch for stress cracks in the mat.
Mat Thickness
A pneumatic roller is key to higher density numbers
have a short window of opportunity be-
fore the temperature drops below 240°.
During this time, the mix should not
shove or check and should remain stable
for compaction process. As it cools and
firms up, the compaction becomes in-
creasingly difficult. Also, you must keep
in mind to consider the ambient air
temperature and surface temperature, all
factors that affect your window of com-
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The thickness of the lift will deter-
mine how your roller operators proceed.
During vibration, the weight with cen-
trifugal force lifts and drops the heavy
steel drum as it moves. Generally, the
operator can control the settings of am-
plitude or “beats” allowing for fine tun-
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