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Dubuque Asphalt Interlayer Open House:
“Build It and They Will Come”

 
Three years ago, the City of Dubuque Engineering and River City Paving (RCP) ventured forth to try a new construction method on busy Central Ave., an arterial street in downtown Dubuque, Iowa. Faced with huge costs to reconstruct hundreds of bad Portland Concrete Cement (PCC) joints, the two entities decided that the rehabilitation of Central Ave. should utilize an asphalt interlayer to reduce the reflective cracking of an asphalt overlay over an aging PCC roadway. The project and the process were both a success. It worked so well that Dubuque Civil Engineer, Jon Dienst, decided to use the same construction method on Central Ave.’s one-way counterpart, White Street. “We saw a significant decrease in both the number and severity of reflective cracks compared to our traditional asphalt overlays,” said Dienst.”

The asphalt interlayer is a fine-graded, high-asphalt content, polymerized hot-mix asphalt (HMA). It is placed in a nominal one-inch thickness over a jointed PCC pavement and then overlaid with a minimum of three inches of traditional HMA. It is placed in the same manner as traditional HMA except that the mix is only static (non-vibratory) rolled. “This particular mix design utilized a PG 64-34 asphalt cement with an optimal asphalt cement content of 8.6%.” said Erv Dukatz, Vice President of Materials and Research at Mathy Construction Co., “We developed a mix for this rehabilitation technique almost a decade ago with tremendous results each time it has been utilized. It is great to see more cities, counties and the Iowa DOT taking advantage of longer pavement performance utilizing the asphalt interlayer.”

After the initial success of the Central Ave project three years prior, Dienst was anxious to repeat the success on White St, Central Ave.’s one way parallel. “When we originally designed Central Ave., it was a straight mill and fill operation. After the initial milling, we were looking at a tremendous amount of PCC joint patching. Instead of doing the time-consuming and more expensive joint patching, we opted to “plunge” mill the joints. We literally placed the mill head over the joint, ground down until we hit something solid, and then filled these joints with HMA. We then utilized the one inch asphalt interlayer to impede the reflective cracking of the three inch asphalt overlay.” 
 
The City of Dubuque, River City Paving, and the Asphalt Paving Association of Iowa hosted an Open House on the White St. project on Sept. 24 to highlight the effectiveness of the asphalt interlayer as a PCC road rehabilitation technique. Over 30 city, county and IDOT personnel came to see how this process is done. “It’s simple to construct,” said Kevin Kueter, Senior Estimator/Project Manager at River City Paving, “and in that simplicity is the key to the success. We utilize the extreme flexibility of the asphalt interlayer to retard the PCC reflective cracks and the traditional asphalt overlay is our wearing course. With proper maintenance, this overlay will last an additional five years or more because of the asphalt interlayer.”

The IDOT has developed a developmental specification (DS-12054) and done an experimental project utilizing the asphalt interlayer on a one mile section on I-35 north of the Mason City, IA. It is performing exceptionally well. In its third summer, the control section with just an asphalt overlay was surveyed with 65 reflective cracks, while the asphalt interlayer section with an overlay only showed 11 cracks. That is an 83% performance improvement over the control section. “Because the interlayer has delayed reflective cracking, we have been able to postpone routine maintenance (crack routing and sealing) on this section of I-35. We can use our limited maintenance funds on other needs. Based on its performance, we are planning to use an interlayer on two additional projects to be let in the near future.” said Mark Callahan, Iowa DOT District 2 Design Engineer.

IDOT Bituminous Engineer, Scott Schram took it a step further, “Having already been through the “wait and see” period, the use of the interlayer is gaining momentum with our designers. This is a much needed tool for increasing our return on investment compared to traditional overlay practice.“

A special thanks is extended to the City of Dubuque Engineering staff, the management and crews of River City Paving and all our attendees for making this open house another great asphalt success story.

 

 For more information on utilizing the asphalt interlayer on your next overlay project, contact the APAI at 515-233-0015 or at apai@apai.net. 

 

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