ULTRA-HIGH PERFORMANCE OVERLAYS (UHPO) GARNERS ATTENTION
A group of interested contractors, IDOT personnel, suppliers and other interested industry leaders met on September 24th to observe and learn about the construction of an Ultra-High Performance Overlay (UHPO) on Interstate 35 in Warren County. The group was instructed on the design, purpose, advantage and uses for this new thin lift overlay by Scott Schram of the Iowa DOT. Scott mentioned that this process has been used in the Northeast United States and in particular downtown New York, NY with good success. Joe Manatt of Manatts, Inc., explained the challenges and how they were addressed in constructing the overlay.
UHPO is an asphalt mixture utilizing PG 76-34 asphalt and 3/8” top size aggregate. While this mixture contained 50% L2 aggregate it was felt that this percentage could be reduced in future applications. The pavement was first milled and then overlaid with a 1 ½” lift for northbound lanes and a 1” lift on the southbound lanes. The highly polymerized oil was difficult to pump resulting is lower plant hourly production rates. Compaction of the final product was achieved with a single pass of a vibratory steel roller. Due to the thin depth of construction, bond with the existing pavement was very important. To insure this bond occurred a “Trackless” Tack was used.
Scott explained that this procedure was chosen with the intent of buying 5+ years of service for a problem area of the interstate. The original PC pavement lasted only 11 years and even though there have been overlays in the past, the bad PC base has required almost annual patching contracts. While the need is for complete reconstruction, the money does not exist to do so for several years. This process offers a lesser cost solution to restore the ride while helping to preserve the pavement. The Iowa DOT plans to let another project in the upcoming December letting.
The consensus of the group was that the finished product looked very good, was smooth and another “Tool” for the already extensive Asphalt Rehabilitation Toolbox.
A special Thank You to Joe Manatt, Scott Schram, the employees of Manatts, Inc. and the Iowa DOT for hosting this interesting and successful Open House.
Click here to view slide show.