I-70 Reconstruction at Stratton Interchange, CO

Project Focus
This $16.1 million reconstruction of I-70 used 412,000 sy of unbonded concrete overlay, and was, notably, the first limited 10-year warranty project bid by CDOT. Previously the state had partnered with the industry through the Colorado-Wyoming Chapter of the ACPA to develop a pilot program for 5-year Materials and Workmanship warranties. For this contract, the contractor was required to determine the thickness of pavement for the project conditions, propose a design flexural strength based on his knowledge of the materials he would use and his construction variability, and then use that strength to determine the thickness from the AASHTO equation using other inputs provided by CDOT. Of course, the acceptance target was then proposed and used in the design. The Contractor then warrants the pavement for 10 years for any warranted defect that exceeds the defined threshold as set forth in the specification. The Contractor bid a lump sum amount to provide the warranty, and the limit of warranty was $1 million by Contract

Schedule & Complexity
The project was constructed with head-to-head traffic crossovers delineated with vertical barricades. The project team completed crossovers and pipe extensions in the winter, allowing an early spring start and completion of the project in late fall, nearly 6 months earlier than specified. We constructed high-speed slip-ramps to enter and exit I-70 at the Stratton Interchange for safe merge. We also reduced the construction zone speed limit from 75 mph to 65 mph to reduce incidence of accidents. The project team distributed public notices encompassing lane changes and other public concerns to increase awareness of the project situation relative to a safe environment. We were able to reduce user costs by completing the project in a single year rather than the two permitted.

Project Details
Construction & Innovation
The concrete was placed using a CMI 550 paver with a Guntert & Zimmerman automatic dowel bar inserter at 38’ width. We achieved better traction by moving the front legs of the paver inward on the existing asphalt pavement. Concrete was mixed in a Rex Model-S plant and hauled to the paver in dump trucks. The project had four overhead bridges with columns that did not allow enough width for the mainline paving machine to pass. Project partnering realigned and transitioned the roadway at these bridges to allow the paver to pass the existing columns. This cooperation expedited the project and improved the quality of the ride for these major transitions. Innovative modifications to the slipform paver were made prior to starting the project, the most significant being the lowering of the machine profile approximately 9 inches from front to back. This "forced" the machine into a lower portion of the leg barrels where there was less room for lateral play resulting in a "snug", tight and accurate slip plane for the machine corrections. This improved the smoothness significantly. The Contractor also employed a Minnich Auto-Vibe system that permitted the operator and the inspectors to monitor the vibrator system continuously.

The Contractor QC program was integral to the internal risk management program necessary since the contractor would be required to fix warranted defects for 10 years acceptance of the pavement. This program included intensive training of all key personnel, as well as a detailed documentation of the testing and inspection regime. The innovations detailed above allowed the Contractor to achieve 87% of the smoothness incentive available for the project, a very credible effort given the nature of a thick overlay paved full-width.

Public Relations
A full-time public relations person distributed information fliers to the local community and manned a quick-response hotline.