About the research
The Central Iowa Expo facility located in Boone, Iowa, needed to be reconstructed in 2012 to provide an improved pavement foundation for pavement with hot mix asphalt (HMA) and portland cement concrete (PCC). This rework created a unique opportunity to conduct pavement foundation research using a range of stabilization construction and testing technologies on about 4.8 miles of roadway. The Iowa Department of Transportation (DOT) initiated a research project to build the pavement foundation layer (Phase I), construction of the pavement layers (Phase II), and performance monitoring of the pavement systems (Phase III). During Phase I, 16 test sections were constructed, that used woven and non-woven geotextiles and geogrids at subgrade/subbase interfaces; 4 in. and 6 in. geocells in the subbase layer + non-woven geosynthetics at subgrade/subbase interfaces; portland cement (PC) and fly ash stabilization of subgrades; PC stabilization of recycled subbase; PC + fiber stabilization of recycled subbase with polypropylene fibers and monofilament-polypropylene fibers; mechanical stabilization (mixing subgrade with existing subbase); and high-energy impact compaction. A series of laboratory tests were conducted to characterize the soils, determine compaction characteristics, unconfined compressive strength tests on chemical stabilized samples, and freeze-thaw durability. In situ strength and stiffness-based test measurements were performed during construction (in July 2012), about three months after construction (in October 2012), seven months after construction (in January 2012) during frozen condition, and about nine to ten months after construction (in April/May 2013) during spring-thaw. During Phase II, asphalt compaction was monitored using intelligent compaction technology along with in situ point testing. Phase III monitoring involved testing on the asphalt layer, conducting ground penetrating radar testing to evaluate layer thicknesses and moisture conditions over time. This project generated significant information regarding the mechanistic properties for pavement foundation support for a range of foundation improvement/stabilization methods. The test sections at this facility are unique in terms of the range of technologies used and for the fact that the performance data particularly isolates the influence of the seasonal changes without any loading. Some significant lessons learned from this project and the limitations of the findings are identified in this report.