An improved mechanistic empirical design procedure for unbonded concrete overlays of existing concrete pavements (UBOLs) should account for the effect of the interlayer on the structural response of the pavement. One approach is to use the Totsky model to characterize the interlayer. The Totsky model treats the interlayer as a bed of springs between two plates and is currently incorporated into the rigid pavement finite element software ISLAB. A difficulty encountered in implementing this model is that there are currently no guidelines as to what the interlayer k-value should be for different types of interlayers. The interlayer can be constructed of new or aged asphalt (open or dense graded) or a nonwoven geotextile fabric. To establish the k-values that accurately characterize each of these materials, an ISLAB model of a laboratory test was created so the k-values could be established by matching the measured and calculated difference between the deflections in the overlay and existing pavement. To supplement the use of the laboratory data in establishing the Totsky interlayer k-value, an analysis was carried out using falling weight deflectometer (FWD) data from UBOLs at the Minnesota Road Research Facility (MnROAD). Analyses were then performed to determine if the difference between k-values for different interlayer materials are statistically significant, and if the results from the laboratory analysis match those obtained from the MnROAD field data. The Totsky k-value recommended for use when modeling the response of an UBOL with an asphalt interlayer is 3500 psi/in and 425 psi/in for a fabric interlayer.
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The authors would like to thank the Georgia, Iowa, Kansas, Michigan, Minnesota, Missouri, North Carolina, and Oklahoma Departments of Transportation. These states participated in the FHWA Pooled Fund Study TPF 5-269 under which this work was performed. The authors would also like to thank the following people for their assistance in their research effort: Andrew Bennett, Benjamin Krom, and John Staton of MDOT; Thomas Burnham, Robert Strommen and Jack Herndon at the MnROAD Research Facility; Rob Golish from MnDOT; the McCrossan Company; Elwood Balog and James Foringer of PennDOT; and Golden Triangle Construction for their assistance. The supply of the nonwoven geotextile fabrics and technical expertise provided by Eric Little, formerly with Propex, was also greatly appreciated.
© National Academy of Sciences: Transportation Research Board 2018.