APPLIED CONSTRUCTION GEOLOGY TO MAXIMIZE PAVEMENT PERFORMANCE

For the past 20+ years I have worked with the carbonate sequence stratigraphy of the geology of Iowa. The state of Iowa has an almost complete Paleozoic carbonate stratigraphic sequence. This makes the Geology of Iowa quite complex. Not only are there differences within the individual rock formations that can affect suitability for construction uses; there is extreme variability in the overall quality of carbonate aggregates from Northeast Iowa to Southwest Iowa. The quality diminishes greatly in the Southwestern part of the state. This means that high-quality aggregates for state and interstate Portland Cement Concrete (PCC) paving projects must be trucked or railed a considerable distance. Iowa is also home to a thick sequence of glacial geology in the Central and Northwestern part of the state that has its own challenges and opportunities. Because of this, recommendations for quarry ledge control and production depths are paramount.

The Iowa DOT has developed an aggregate quality approval process that uses low-tech physical and high-tech chemical testing methods. Examples of the high-tech chemical testing are X-ray Fluorescence; X-ray Diffraction; Thermogravimetric Analysis and Iowa Pore Index testing. Many years of laboratory research and hundreds of pavement performance reviews have resulted in a Salt-susceptibility Quality number algorithm that uses chemical and physical test results to characterize suitability of aggregates for this purpose. The presentation will cover the details of this work and the details of the aggregate quality approval process that has been working successfully for Iowa. By using this system, we strive to maximize the longevity of the pavements in Iowa and also maximize Iowans’ tax dollars spent on infrastructure.