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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 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.
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