Center for Earthworks Engineering Research A Comparison of Pavement Foundation Stabilization Technologies Peter J. Becker, M.S. Graduate Research Assistant Center for Earthworks Engineering Research (CEER) 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

Center for Earthworks Engineering Research 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 2

Center for Earthworks Engineering Research The testing area encompasses 24 test sections distributed over 12 north-south roads 3

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

Center for Earthworks Engineering Research 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) 5

Center for Earthworks Engineering Research Performance was measured using the following in situ testing equipment 6 Falling Weight Deflectometer (FWD) Dynamic Cone Penetrometer (DCP)

Center for Earthworks Engineering Research Mechanical stabilization of subgrade is the mixture of good quality geomaterial with poor quality subgrade 7

Center for Earthworks Engineering Research Geocells use confinement to strengthen geomaterials 8

Center for Earthworks Engineering Research Geotextile fabrics provide separation and filtration for pavement layers 9 Woven Geotextile Fabric Non-woven Geotextile Fabric

Center for Earthworks Engineering Research Polymer grids provide planar reinforcement to pavement layers 10

Center for Earthworks Engineering Research Cement stabilization (of subbase) increases strength and stiffness. Fiber stabilization increases toughness, shear strength. 11 FP FibersMP Fibers

Center for Earthworks Engineering Research Recycled subbase test section included 6 in. nominal subbase below modified subbase layer 12

Center for Earthworks Engineering Research Cement stabilization (of subgrade) increases strength and stiffness 13

Center for Earthworks Engineering Research Fly ash stabilization (of subgrade) increases strength and stiffness 14

Center for Earthworks Engineering Research Cement stabilized sections yielded comparatively higher modulus values overall from FWD testing 15

Center for Earthworks Engineering Research Cement stabilized sections yielded comparatively higher modulus values overall from DCP testing 16 Modified Subbase Layer Subgrade or Recycled Subbase Layer

Center for Earthworks Engineering Research Investments in foundation stabilization will increase modulus and can potentially lead to better pavement performance 17

Center for Earthworks Engineering Research Correlations were made between FWD modulus and DCP penetration index 18 Modified Subbase Layer Subgrade or Recycled Subbase Layer

Center for Earthworks Engineering Research Multivariate statistical analyses showed that the surface subbase elastic modulus layer becomes statistically insignificant during the spring thaw 19 TermEstimate Standard Error t RatioProb. > t Statistically Significant R 2 Adj. October 2012 Testing log(E FWD ) = b 0 + b 1 ∙log(PI CLS ) + b 2 ∙log(PI SG or RSB ) bobo <0.0001Yes b1b Yes b2b Yes April 2013 (Spring Thaw) Testing log(E FWD ) = b 0 + b 1 ∙log(PI CLS ) + b 2 ∙log(PI SG or RSB ) bobo <0.0001Yes 0.69 b1b No b2b <0.0001Yes

Center for Earthworks Engineering Research 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 20

Center for Earthworks Engineering Research 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) 21

Center for Earthworks Engineering Research 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 22 Thank You for your attention!