Contractor penalized tens of thousands of dollars for using toy
gun.
That’s about the gist
of it after you hear a disgruntled employee’s story. Justifiably
so, the employee wishes to remain anonymous. He and others on the
QC staff advised of the necessity of the roller operators to continuously
monitor the mat temperature to assist in mat density control. A
continuous temperature indicator system would have paid for itself
tens of times over. The gun being used is good for spot checks.
The key here is continuous checks are better than spot checks. Guns
are not continuous. QC should layout the rolling patterns, frequencies,
amplitudes, etc, and temperature ranges to the roller operator.
With an EZ-Temp, the roller operator can tell continuously when
he’s too close or too far from the paver. Nobody has to be there
to tell him, “Get on, and Get off, Faster, Slower”. No gun has to
be searched for. The operator does not have to stop and shoot. The
indicator is mounted to the dash and continuously reports. The roller
operator can do his job. Scherocman explains below the Three Temperature
Zones and asks, “How do you roll them to achieve density?”
What are the three temperature zones? A mix that has tender
properties can still be compacted to the proper density by taking
advantage of its three temperature zones. In the first, or upper,
zone, the mix is fairly stable during the compaction process when
laydown occurs within the temperature range of 285 to 320° F (140
to 160° C), down to about 240° F (115° C). In this range, the HMA
will normally not shove or check under the rollers regardless of
whether a vibratory or static steel wheel roller is used.
The middle temperature zone — the problem range — extends from approximately
240°F (115° C) down to about 195° F (90° C). In this range, the
mix will shove, move and check under the applied compactive effort.
The mix will
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crawl longitudinally,
move laterally or transversely, and widen out if the edge of the roller
is not properly positioned along the unsupported edge of the mat.
The mix normally will not move in this intermediate temperature zone,
however, when compacted with a pneumatic tire roller. The lower temperature
zone extends from the end of the tender, or intermediate temperature
zone down to approximately 160° F (70° C) or lower. Within this temperature
range, the mix is cool enough to regain the internal stability necessary
to support the weight of the compaction equipment.
How do you roll them to achieve density? To compact a tender
Superpave mix, a contractor has two choices. First, he or she can
compact the mix in the upper and/or lower temperature zones where
the mix is internally stable and does not move or shove. Second, if
he or she has to roll the mix while it is within the middle temperature
zone, then he or she can use a pneumatic tire roller as the intermediate
roller since the mix will not typically shove in front of the rubber
tires, as it will in front of the drum of a steel wheel roller.
The paving industry has adopted the temperature gun because it is
inexpensive and ready to use. The gun falls short of enabling the
user to do the job right for two reasons. 1). The roller operator
only knows the temperature when he is reading the gun or someone is
telling him the gun reading. It’s like using a picture camera to do
the job required of a movie camera. Guns take snapshot temperature
readings when a continuous reading is required. 2). Notice how the
temperature reading from the gun changes dependent on it’s distance
from the mat. Hinge your decision on $89.50 or $995.00 and you may
be spending $995.00 tens of times over instead of not spending it
at all. |