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  1. A Comparison of Pavement Foundation Stabilization Technologies Peter J. Becker, M.S. Graduate Research Assistant Center for Earthworks Engineering Research (CEER) pbecker@iastate.edu David J. White, Ph.D., P.E. Associate Professor and holder of Richard L. Handy Professorship Director, Center for Earthworks Engineering Research (CEER) Department of Civil, Construction and Environmental Engineering Iowa State University djwhite@iastate.edu

  2. This presentation will compare the performance of different pavement foundation stabilization techniques used at the Central Iowa Expo (CIE) roadway reconstruction • Project overview • Performance (as constructed, freeze-thaw, & recovering) • Cost analysis

  3. The testing area encompasses 24 test sections distributed over 12 north-south roads

  4. Prior to reconstruction, each test section comprised the following cross section Existing Profile GRANULAR BASE A-1-a (SM) 8” CHIPSEAL COATING SUBGRADE A-6(5) (CL) BIAXIAL GEOGRID

  5. Roadways were reconstructed with different pavement foundation stabilization techniques • Control • Mechanical stabilization of subgrade (Mix A-1-a with A-6(5)) • Geocell-reinforced subbase (4 in. and 6 in.) • Geotextile fabric (non-woven and woven) • Polymer grid (biaxial and triaxial) • 5% cement stabilized subbase • 5% cement and 0.4% fiber stabilized subbase • Fibrilated polypropylene (FP) and monofilament polypropylene (MP) fibers • Recycled subbase • 10% cement (PC) stabilized subgrade • 10%, 15%, and 20% fly ash (FA) stabilized subgrade • High Energy Impact Compaction (Converted to control section)

  6. Performance was measured using the following in situ testing equipment Dynamic Cone Penetrometer (DCP) Falling Weight Deflectometer (FWD)

  7. Mechanical stabilization of subgrade is the mixture of good quality geomaterial with poor quality subgrade

  8. Geocells use confinement to strengthen geomaterials

  9. Geotextile fabrics provide separation and filtration for pavement layers Woven Geotextile Fabric Non-woven Geotextile Fabric

  10. Polymer grids provide planar reinforcement to pavement layers

  11. Cement stabilization (of subbase) increases strength and stiffness. Fiber stabilization increases toughness, shear strength. FP Fibers MP Fibers

  12. Recycled subbase test section included 6 in. nominal subbase below modified subbase layer

  13. Cement stabilization (of subgrade) increases strength and stiffness

  14. Fly ash stabilization (of subgrade) increases strength and stiffness

  15. Cement stabilized sections yielded comparatively higher modulus values overall from FWD testing

  16. Cement stabilized sections yielded comparatively higher modulus values overall from DCP testing Modified Subbase Layer Subgrade or Recycled Subbase Layer

  17. Investments in foundation stabilization will increase modulus and can potentially lead to better pavement performance

  18. Correlations were made between FWD modulus and DCP penetration index Subgrade or Recycled Subbase Layer Modified Subbase Layer

  19. Multivariate statistical analyses showed that the surface subbase elastic modulus layer becomes statistically insignificant during the spring thaw

  20. A summary of key findings are as follows: • During spring thawing, each test section experienced approximately 2 to 9 times reduction in FWD modulus or CBR • Cement stabilized sections perform comparatively better than all other test sections, according to FWD and CBR measurements • Investments in pavement foundation stabilization techniques can potentially result in better pavement performance, even during spring thawing • Elastic modulus of surface granular layers become statistically insignificant to overall modulus during spring thaw

  21. Performance of the stabilized foundations will be monitored in the near and distant future • Sections were paved with, PCC, HMA, and WMA this summer • Long term performance study • Laboratory studies(In progress)

  22. Acknowledgments • The presenters would like to thank… • The Iowa Department of Transportation • Mark Dunn, P.E. • Jesus Rodriguez • Center for Earthworks Engineering Research (CEER) students • Lance Keltner • Nick Buse • Jinhui Hu • Yang Zhang Thank You for your attention!