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Thin lifts are more sensitive to vibratory rolling. Very thin lifts (less than 1 inch) can be damaged by the screed dragging large particles. If the lift depth is less than about twice the maximum aggregate size, the HMA may tear under the paver screed. Thin lift construction produces greater screed wear. The thin lifts cool quickly, resulting in less time available to get density before the overlay reaches the temperature at which rolling must stop. Thin lifts require less HMA per foot of road length than thick lifts, resulting in faster paver speeds (in excess of 70 ft/min) which can make it difficult for rollers to keep up. Thin-lift paving, such as that seen in non-structural overlays, presents several construction concerns. NAPA has produced technical information on thin lifts. In 1995 the National Asphalt Pavement Association (NAPA) reported that thin lift overlays are employed to improve ride smoothness, correct surface defects, improve safety characteristics such as skid resistance and drainage, enhance appearance, and reduce road-tire noise. The chemistry of liquid asphalt has been enhanced by a new generation of asphalt modifiers, boosting the performance of Superpave mixes (Superpave Plus), open-graded friction courses, and thin-lift overlays.
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The technology of HMA is making thin lifts more applicable. The definition of thin-lift overlays varies, but the lift usually is from 1/2- to 1 1/2-inch in depth. Stung by the rising popularity of high-performance, polymer-modified chip seals, the asphalt industry has vigorously researched and promoted thin-lift HMA overlays.
#ASPHALT TEXTURE SMOOTH HOW TO#
Although we are not moving ahead with a method spec for cold milling at this time, we will continue to study how to get the best smoothness for our customers." There's no doubt that the milled surface with the fine textured milling drum is smoother and more uniform than the surface with the conventional milling drum. We also like the non-contact leveling systems we saw. "We like the 12-foot drum because we eliminate the two machines, the overlapping of the joint and the possibility of a mismatched cross slope. "As we vary from interstate overlays with mill, binder and surface layers to mill-and-fill with thin overlay, we are paying special attention to the quality of cold milling, or milling for smoothness," Egan says. "We are looking at use of full-lane drums, closer teeth spacing and forward speed as it relates to teeth spacing," says Brian Egan, P.E., field operations engineer, Tennessee DOT. That's what we were looking to correct."Īs the result of this job and a few others, the state of Tennessee is taking a close look at its specs for milling limited access highways. We know now that the milled surface reflects through that inch and a quarter, and the fine-textured milling drum does not. "We found that when this is done with a conventional milling head, the surface will ravel and you can feel the milled surface reflecting through the fresh surface. "The state is doing a lot of thin overlays, in which we take off an inch and a quarter and put an inch and a quarter right back," says Michael Eubank, director of field management, Eubank Asphalt Paving and Sealing, Charlotte, TN. The firm met or exceeded smoothness specs of less than 35 inches per mile using the half-car International Roughness Index (IRI) measurement, and Eubank received the bonus on every section. Utilizing a Wirtgen W 2200, Eubank Asphalt Paving fine-milled 40 lane miles of I-40 - a 10-mile interstate mill-and-fill project - to a depth of 1 1/4 inches using a full-lane, fine-texture drum with tooth spacing at 5/16 inches, approximately twice as dense a configuration as the conventional 5/8-inch spacing.
#ASPHALT TEXTURE SMOOTH FULL#
A Tennessee contractor recently won a $58,000 smoothness bonus on a thin-lift hot mix asphalt (HMA) overlay by using a fine texture drum the full width of a lane on I-40 in Cheatham and Williamson counties in central Tennessee.