Iowa Department of Transportation : A Design for Growth, 1971

This report has been prepared to provide a succinct documentation of the results of an intensive "finding" as to the requirement for an Iowa Department of Transportation, the recommended general organizational characteristics, and the implementation process requisite to instituting an Iowa Department of Transportation. This report specifies, in summary, the systematic procedure employed in the analysis, followed by a presentation of the fundamental concepts associated with a department of transportation and documentation of the "need" for a state department of transportation. The majority of the report is devoted to presentation of a best judgment as to how an Iowa Department of Transportation should be organized and implemented. The report concludes with a discussion of a recommended approach to the implementation of the department, and issues and recommendations for review.

Validation of Gyratory Mix Design in Iowa, TR-667, 2016

The design number of gyrations (Ndesign) introduced by the Strategic Highway Research Program (SHRP) and used in the Superior Performing Asphalt Pavement (Superpave) mix design method has been commonly used in flexible pavement design throughout the US since 1996. Ndesign, also known as the compaction effort, is used to simulate field compaction during construction and has been reported to produce air voids that are unable to reach ultimate pavement density within the initial 2 to 3 years post-construction, potentially having an adverse impact on long-term performance. Other state transportation agencies have conducted studies validating the Ndesign for their specific regions, which resulted in modifications of the gyration effort for the various traffic levels. Validating this relationship for Iowa asphalt mix designs will lead to better correlations between mix design target voids, field voids, and performance. A comprehensive analysis of current Ndesign levels investigated the current levels with existing mixes and pavements and developed initial asphalt mix design recommendations that identify an optimum Ndesign through the use of performance data tests.