A Revised Thin and Ultra-Thin Bonded Whitetopping Design Procedure. Submitted by. (ph) ( )

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1 A Revised Thin and Ultra-Thin Bonded Whitetopping Design Procedure A Paper Submitted to the Transportation Research Board for Publication and Presentation at the 0 Transportation Research Board Annual Meeting Submitted by Julie M. Vandenbossche, Ph.D., P.E. University of Pittsburgh 0 Benedum Hall Pittsburgh, PA (ph).. ( ) jmv@engr.pitt.edu Nicole Dufalla University of Pittsburgh Benedum Hall Pittsburgh, PA (ph)..00 ( ) nid@pitt.edu and Zichang Li University of Pittsburgh Benedum Hall Pittsburgh, PA (ph)..0 ( ) zil@pitt.edu Submission date: August, 0 Number of figures: Number of tables: Word count:,+,00 =, TRB 0 Annual Meeting

2 ABSTRACT Design procedures for bonded whitetopping overlays were developed based on the assumption that failure mechanisms were a function of the overlay thickness, namely thin whitetopping (TWT) with longitudinal cracking and ultra-thin whitetopping (UTW) with corner cracking. However, field data from whitetopping sections indicated that the actual failure modes are dictated by slab size rather than overlay thickness. The revised procedure presented here for TWT and UTW includes four primary enhancements to the PCA and CDOT procedures that have been traditionally used:.) the failure mode is dictated by the joint spacing and not the overlay thickness;.) the stress adjustments factors have been more extensively calibrated;.) the equivalent gradients to be used as the design input are defined based on the pavement structure and geographical location of the project and.) the change in HMA stiffness with changes in temperature is considered. Comparisons made between the performance predicted using the revised procedure and the actual performance for four separate projects showed the predicted thicknesses to be reasonable. It was also found that the predicted thickness obtained using the revised procedure was sensitive to HMA thickness, the level of traffic and the modulus of rupture (MOR) of the PCC, as would be expected. Word count: TRB 0 Annual Meeting

3 INTRODUCTION Bonded whitetopping, a rehabilitation procedure consisting of a thin Portland cement concrete (PCC) layer placed on top of deteriorated hot-mixed asphalt (HMA) pavement, has become an increasingly popular rehabilitation technique in the United States. Bonded whitetopping has been historically divided into two separate categories; ) thin whitetopping (TWT) (overlay thickness greater than in [0. mm] but less than in [. mm]) and ) ultra-thin whitetopping (UTW) (overlay thickness between to in [0. to 0. mm]). The design procedure most commonly used for UTW in the United States is the Portland Cement Association (PCA) procedure (). The procedure is also the foundation of what is currently programmed into the American Concrete Paving Association application frequently used by pavement engineers today (). This procedure was intended for overlays between and in [0. to 0. mm] thick with smaller panel sizes ( in [. mm] or less). The PCA procedure assumes the mode of failure for UTW is corner cracks and that the critical loading condition is a corner wheel loading along with a negative temperature gradient (top of the slab is cooler than the bottom). The Colorado Department of Transportation (CDOT) procedure, which was developed in () and later revised in 00 () is most commonly used in the United States for designing TWT. This design procedure was intended for overlays ranging between to in (0. to 0. mm) and joint spacings up to ft (. m) (). The CDOT procedure assumes the mode of failure for TWT is transverse cracking. The critical load condition is assumed to be a wheel load located adjacent to the longitudinal joint at midslab in the presence of a positive temperature gradient (top of the slab warmer that the bottom). The CDOT and PCA procedures have served the pavement community well for many years but they do have several limitations, as will be described below. To address these limitations, a revised design procedure was developed that incorporates much of the framework of the PCA and CDOT procedures but also addresses some of these limitations. The primary limitations of these two procedures are discussed below. A review of the performance data from the many constructed UTW and TWT overlays near the end of their intended service-life was performed (). It was observed that the design procedures traditionally used do not reflect the actual failure mechanisms experienced by UTW and TWT. The first observation made was that the actual failure modes of these overlays are dictated by slab size rather than overlay thickness, as has been traditionally assumed. For smaller slabs (e.g. < -ft -ft [. m. m] joint spacings), the longitudinal joints lie within the wheelpath, which results in corner cracking. The wheelpath for larger slabs (e.g. -ft -ft [. m. m] slabs), falls in the central portion of the slab. Cracks then initiate at the transverse joint and propagate mainly along the wheelpath to form longitudinal cracks but may occasionally turn to adjacent slab to form the diagonal shear cracks. The performance data validates that the cracking develops in the wheelpath. The revised design procedure, which will be presented here, acknowledges these failures modes observed in the field. The PCA and CDOT design procedures also simplify the effect of temperature on the HMA stiffness by using a constant HMA elastic modulus regardless of temperature at the time of loading. However, the damage prediction for the whitetopping overlay varies significantly with the HMA stiffness. The magnitude of the critical stress for the overlay, as well as the accumulated fatigue damage, increases with decreasing HMA stiffness. It is well known that the stiffness of HMA decreases as temperature increases. Therefore, much more fatigue damage in the PCC overlay develops in the summer than the winter or in warmer climates, such as in TRB 0 Annual Meeting

4 Miami, FL, than colder climates, such as in Minneapolis, MN. Therefore, it is important to account for the dependency of HMA stiffness on temperature. The revised design procedure presented here accounts for both seasonal and hourly variations in the HMA resilient modulus as a function of changes in temperature. Temperature gradients also significantly contribute to the generation of stress in the PCC overlay. Slab curling magnifies the load-induced stresses and accelerates the accumulation of fatigue damage. Although whitetopping is usually constructed with small slabs (e.g. -ft -ft/ - ft -ft [. m. m/.. m]) to decrease the magnitude of environmental stresses, the contribution of these stresses in the total design stress is still significant. Despite the significance of the temperature gradient in stress predictions, values appropriate for each of the broad range of climatic conditions encountered throughout the United States were not previously available. This revised procedure includes localized effective temperature gradients for the climatic conditions found throughout the United States as a function of the design features of the pavement structure. Finally, this design procedure has been calibrated using field performance data. As additional performance data becomes available, a recalibration should be performed. This along with the three enhancements described has allowed for the development of a more generalized and versatile design procedure for UTW and TWT. The structure of the revised design procedure is described below. A sensitivity analysis was then performed and comparisons are made between the predicted design thicknesses obtained from this procedures and those using the PCA (for designing UTW) and CDOT (for designing TWT) procedures FRAMEWORK FOR THE REVISED PROCEDURE The revised design procedure is a spreadsheet based procedure, which provides the predicted overlay design thickness for bonded whitetopping based on the predefined inputs. The inputs used are the same as those used in the PCA and CDOT design procedures, with a couple of exceptions. First, the HMA stiffness is determined internally based a virtual new HMA mixture design using the geographical location of the project and is then adjusted for aging and fatigue using the same models incorporated in the MEPDG. Therefore the geographical location is also an input that must be defined for this revised procedure. The asphalt parameters used included a standard aggregate gradation and a binder selected based on the regional climate conditions of the project using LTPP Bind. The percent fatigue cracking in the HMA layer prior to the placement of the overlay must also be known or estimated. The revised procedure combines the PCA and CDOT procedures but provides the additional enhancements described below. ENHANCEMENTS Stress Prediction The stress prediction equation to be used within the revised design procedure is selected based on the spacing and not the overlay thickness because of the field observation that the failure mode is dictated by slab size rather than PCC thickness. The PCA stress prediction model () is used for predicting corner cracking based on a corner load applied in the presence of a negative gradient, while the CDOT model () is used for predicting transverse/longitudinal cracking based on an edge load in the presence of a positive gradient. The CDOT stress prediction model was developed based on the tensile stress in the longitudinal direction at the bottom of the overlay at midslab along the lane shoulder. A number of finite element runs were performed which revealed that the stress prediction obtained using the CDOT model is comparable to those TRB 0 Annual Meeting

5 generated in the transverse direction at the bottom of the overlay in the wheelpath and adjacent to the transverse joint, which contribute towards longitudinal crack development. This can be attributed to the fact that edge support is considered in the CDOT stress prediction model and that for these thin bonded overlays most of the load is transferred across the joints through the HMA layer. Therefore, the effect of the difference in the load transferred across the transverse joint as compared with the longitudinal joint is minimal. Based on the above, the PCA stress prediction model is used when the joint spacing is <. ft(. m) and the CDOT model is used when the joint spacing >. ft (. m) in the revised procedure, as shown in Figure. The damage induced by each load application is then accumulated using the American Concrete Paving Association (ACPA) fatigue model (). Inputs Jt. Spacing<. ft Jt. Spacing>. ft PCA Model Stress for corner cracks Stress for transverse and longitudinal cracks CDOT Model Figure. Design framework. ACPA Model Fatigue model Calibration of Stress Adjustment Factors Field tests and experimental analyses have both shown that TWT and UTW are partially bonded composite pavements; that is, the slab delaminates and the intended full bond is not maintained across this interface.(). The partial bonded condition is used to better simulate field conditions because the bonded system does not act as a perfect rigid connection. Both the PCA and CDOT stress prediction models are based on fully bonded conditions and stress adjustment factors are then used to account for the partial bonding that is exhibited in the field. The original stress adjustment factors used in the PCA and CDOT procedures were established based on a limited amount of instrumented overlays. The degree of partial bonding exhibited when measuring the response of the overlay is a function of the relative flexural stiffness between the two overlays. The flexural stiffness of a layer is primarily dictated by the thickness of that layer. Therefore it is reasonable that stress adjustment factors should be established as a function of the overlay and HMA thickness. The availability of distress data that was not available at the time the original models were developed makes it possible to establish stress adjustment factors as a function the pavement structure. The stress adjustment factors are established by calibrating the predicted performance in terms of fatigue damage to field distress measurements (percentage of slabs cracked). A fatigue damage of 00% was correlated to % slabs cracked. The projects used to populate the calibration database for the development of the stress adjustment prediction equations are shown in Table. Figure presents the performance data and the predicted fatigue for Cells,, and, respectively. h PCC TRB 0 Annual Meeting

6 TABLE: Whitetopping projects included in the calibration database for determining the stress adjustment factors. State Project h PCC, in h HMA, in Slab size, ft ft F Stress Cell, MnROAD 0. Cell, MnROAD.0 Minnesota Cell 0, MnROAD. Cell, MnROAD. Cell, MnROAD 0. Missouri Intersection of SR and SR.00 Illinois Highway - Piatt County...0 Highway - Cumberland County....0 US - Section...0 US - Section... Colorado US - Section.. SH - Section... SH - Section...0 SH - Section... NOTE: in =. mm; ft = 0. m 00,000,000,000 0,000,000 0% 0% 00,000,000,000 0,000,000 0% 0% 0 Percentage of cracking % 00% % 00% 0% % 0% % 0% 0% 0% 0% 0% 0%.0E+0.0E+0.0E+0 ESALs Cell : in; ft ft Cell : in; ft ft Cell : Predicted fatigue Cell : Predicted fatigue Critical limit (a) Projects with a joint spacing <. ft. (b) Projects with a joint spacing >. ft. NOTE: in =. mm; ft = 0. m Figure. Performance data and predicted fatigue of Cells,, and. By using the database of stress adjustment factors generated, regression equations and were developed. Using the R as an indicator of goodness-of-fit, Figure shows a better fit for slabs with joints spacings >. ft(. m) (R = 0.) than for joint spacings less than <. ft (. m)(r = 0.). This relationship can be improved upon as more performance data becomes available. for a joint spacing greater than ft (. m): 0.. h. h. h + h 000 Fatigue Percentage of cracking 0% % 0% 0% % 0% 0% 0%.0E+0.0E+0.0E+0 h 0% Fatigue 0% ESALs Cell : in; ft ft Cell : in; ft ft; Cell : Predicted fatigue Cell : Predicted fitigue Critical limit () TRB 0 Annual Meeting

7 for a joint spacing less than or equal to ft (. m): h h h.0 log h + 0 h + h. 00 () 0 0 Figure shows the adjustment factors established by matching the predicted fatigue damage to the performance data. Equations and are incorporated into the revised design procedure. This allows stress adjustment factors used for equating the predicted stress representing a fully bonded overlay to that of a partially bonded overlay to be obtained as a function of the pavement structure. Calculated stress adjustment factor Stress adjustment factor (Joint spacing > ft x ft) Generated stress adjustment factor (a) slabs with joint spacings>. ft (b) slabs with joint spacings<. ft NOTE: in =. mm; ft = 0. m Calculated stress adjustment factor Figure : Stress adjustment factors Generated stress adjustment factor Effective temperature gradient Temperature gradients cause the slab to curl creating an environmental stress in addition to the stress generated as the result of traffic loads. In the available structural models for bonded whitetopping, an effective linear temperature gradient (EELTG) is required to quantify the contribution of temperature gradients on the total stress. The EELTG represents a single equivalent linear gradient that can be applied to all load applications and produce the same damage that would develop if the hourly variation in the temperature distribution was considered. In PCA and CDOT procedures, little guidance is provided on what value should be used as for this input. Appropriate values have been established in the revised procedure. The following discussion describes how this was performed. It should first be noted that since the temperature variation through the slab is nonlinear, an accurate estimate of environmental stress is not possible when quantifying the temperature distribution using a linear temperature gradient (difference between the temperature at the top and bottom of the slab normalized by the slab depth). Therefore, an equivalent linear gradient was used for this analysis. This equivalent linear gradient was established based on equivalent strain and therefore, the linear gradient providing the same deformation in the slab as the nonlinear temperature distribution was defined as the equivalent linear gradient. It should be Stress adjustment factor (Joint spacing ft x ft) TRB 0 Annual Meeting

8 0 noted that the difference between an equivalent stress and an equivalent strain approach produced comparable equivalent linear gradients. The framework used to establish the EELTG is illustrated in Figure. A database was first populated to produce virtual whitetopping projects in different locations representing the broad range of climatic conditions present across the continental United States. For each location, a number of virtual whitetopping projects were developed to represent a range of structural design features, such as PCC overlay thickness, existing asphalt thickness, etc. The nonlinear temperature gradient for each virtual whitetopping project was then established on an hourly basis using the Enhanced Integrated Climatic Model (EICM) (). The hourly nonlinear temperature gradients were then converted to hourly equivalent linear temperature gradients (ELTGs) based on strain equivalency. Finally, the EELTG was determined for each different project. It is the equivalent linear temperature gradient that, when applied throughout the design life, results in the same fatigue damage as if the hourly linear temperature gradients were considered. Using this database EELTGs, a relationship was established between the EELTG and the climatic conditions at the project location and the structural features of the PCC overlay. More details regarding establishing this input can be found in the reference Mu and Vandenbossche, (0)(). TRB 0 Annual Meeting

9 0 0 Figure : Methodology used in establishing the effective equivalent linear temperature gradient. Temperature dependency of HMA stiffness The HMA modulus changes with seasonal and daily temperature variations. However, in all available design procedures, a constant HMA modulus is used with little guidance on how this should be established. Assuming a constant HMA modulus results in uniform fatigue consumption throughout the year when in fact there is an increase in the fatigue damage during the summer months and a decrease during the winter months. In this design procedure, HMA modulus adjustment factors are used to account for both monthly and hourly temperature fluctuations. These adjustment factors are established as a function of the thickness of the concrete and HMA layers and the monthly ambient temperature for the project location. The additional details on how these adjustment factors were established can be found in the reference by Barman et al. (0)(). PROCEDURE VALIDATION Design Examples In order to validate this revised procedure, predicted overlay thicknesses obtained from the revised procedure were compared with actual performance data. They were also compared with the overlay thicknesses obtained from the PCA () and CDOT () procedures, which have been traditionally used. The projects selected for evaluation represent a large range of climates and overlay designs. A complete set of design information was not available for all projects so, when necessary, these values were estimated based on the information that was available. The project information used is summarized in Table with the estimated values provided in italics. TRB 0 Annual Meeting

10 0 0 TABLE : Summary of design input and output data for whitetopping design examples Project Number Road Segment Highway- NY-0 and Cell, US 0 SH- MnROAD Location Cumberland Rochester, Minneapolis, Neosho, MO County, IL NY MN Design Life, years Traffic One-way ADT,00,0,000,00 Estimated Design ESALs 00,000 0,000,00,000,000 HMA Layer Condition Adequate Marginal Adequate Marginal Post Milling HMA.. 0. Existing Thickness, in Structure HMA Poisson s Ratio Properties Modulus of Subgrade Reaction, psi/in Average -day flexural 0 0 strength, psi Average -day,000,000 PCC Overlay compressive strength, psi Properties Estimated PCC Elastic,0,000,00,000,0,000,00,000 Modulus, psi Coefficient of Thermal..0.. Expansion, 0- in/ F/in Joint Spacing, ft Revised Procedure, in...0 Predicted PCA Procedure, in.0. Thickness CDOT Procedure, in.0.0 Constructed Thickness, in Performance 0.% cracks Few corner 0% cracks.% cracks after years cracks after years after 0 years NOTE: in =. in; psi/in = 0. kpa/mm; psi =. kpa; 0 - in/ F/in =. - m/ C/m; ft = 0. m; Maximum or minimum allowed by the design procedure indicating that the actual predicted thickness is greater than (max.) or less than (min.) the thickness reported. Prediction accounts for the use of structural fibers Adequate represents existing HMA pavements exhibiting <% fatigue cracking and Marginal represents 0% fatigue cracking. Comparisons can made between the predictions provided by the revised procedure and those obtained using the design procedure that has been traditionally used (the PCA procedure for designing UTW and the CDOT procedure for TWT) with the results provided in Table. The revised procedure appears to have provided reasonable overlay thicknesses for each of the four projects. It can also be seen that the traditional procedures tend to over predict the performance when the milled HMA layer is thick, as is observed with projects and. These traditional procedures also tend to under predict the performance when the milled HMA layer is too thin, as is observed with projects and. The actual design thickness predicted for project using the CDOT procedure was 0. in (. mm) but a minimum value of in (0. mm) was used since the procedure is not valid for overlays less than in (0. mm). The calibration of the stress adjustment factors keeps the predicted thicknesses provide by the revised procedure more stable at these extreme ranges of the HMA thicknesses. The predicted overlay thicknesses from the traditional and revised procedure are more similar when the HMA thickness is moderate (around in [. mm]). It is interesting to note that the average milled HMA thickness for the instrumented sections used to establish the stress 0 TRB 0 Annual Meeting

11 0 0 0 adjustment factors was in (. mm) for the CDOT procedure ()and ranged between and in [. to. mm] for the PCA procedure(). Sensitivity Analysis An additional evaluation of the revised design procedure is performed by analyzing the sensitivity of the design inputs on the predicted overlay thickness. To do this, standard values were established for each input and these values are summarized in Table. TABLE. Summary of standard input values used in the sensitivity analysis. Standard Input Sensitivity Range Station Minneapolis, MN Latitude (degree). Climate Longitude (degree) -. Elevation (ft) AMDAT Region ID Sunshine Zone Traffic Design ESALs,000,000 0,000 0,000,000 Existing HMA Condition Adequate Marginal Existing Post Milling HMA Thickness (in).0.0. Structure HMA Poisson s Ratio (default 0.) 0. Properties Modulus of Subgrade Reaction (psi/in) 0 0, 0 PCC Overlay Properties Average -day flexural strength (psi) 0 0, 00 Estimated PCC Elastic Modulus (psi),000,000 Coefficient of Thermal Expansion (0- in/ F/in)..0,.0 Joint Spacing, ft, NOTE: in =. in; psi/in = 0. kpa/mm; psi =. kpa; 0 - in/ F/in =. - m/ C/m; ft = 0. m; Traffic Figure shows the required overlay thickness as a function of level of traffic for each of the design procedures. The first observation that can be made is that the revised procedure predicts a lower overlay thickness when the joint spacing is increased from ft to ft (. to. m). This reflects the field performance observed (). Increasing the joint spacing to ft substantially decreases the number of edge and corner loadings that occur since joint spacings less than ft will always result in a longitudinal joint in the wheel path. Increasing the joint spacing also increases the curling stresses but this effect is minimal since curling stresses are still quite low when the joint spacing is only ft (. m). Therefore, the net effect is an increase in service life when the joint spacing is increased from ft to ft (. m to. m). This is not reflected in the PCA and CDOT design procedures since the mode of failure is not dictated by the panel size but the overlay thickness. While the increase in service life for larger slab sizes is counterintuitive to expected performance, calibration of the model with field performance data ultimately led to the improved performance for larger slabs. HMA thickness The revised procedure tends to predict higher overlay thicknesses for the -ft (. m) joint spacing but lower overlay thicknesses for the -ft (. m) joint spacings. This trend is also reflected in Figure, which depicts the predicted thickness as a function of the HMA thickness. The sensitivity of the CDOT and PCA procedures is quite apparent. As previously mentioned, the calibrated stress adjustment factors incorporated into the revised procedure helps eliminate TRB 0 Annual Meeting

12 this response in the revised procedure. Additionally, to ensure that the structural capacity of the HMA layer is not overestimated, the effective HMA thickness is limited to inches. PCC thickness, in PCA- ft x ft CDOT- ft x ft Revised Procedure- ft x ft Revised Procedure- ft x ft 0 0,000 00,000,000,000 0,000,000 ESALs NOTE: in =. mm; ft = 0. m Figure. PCC design thickness with respect to design ESALs. PCC thickness, in Revised Procedure- ft x ft Revised Procedure- ft x ft CDOT- ft x ft PCA- ft x ft HMA Thickness, in NOTE: in =. mm; ft = 0. m Figure. PCC design thickness with respect to HMA layer thickness. PCC Modulus of Rupture The effect of concrete strength on the predicted overlay thickness is shown in Figure a and b. As would be expected, all of the procedures are a quite sensitive to the PCC strength. Figure b TRB 0 Annual Meeting

13 shows that the revised procedure is a bit more sensitive to changes in the strength of the PCC, when compared to the CDOT procedure. Revised Procedure, MOR = 0 psi Revised Procedure, MOR = 00 psi PCA, MOR = 0 psi PCA, MOR = 00 psi PCC thickness, in 0 0,000 00,000,000,000 0,000,000 ESALs a.) -ft (. m) joint spacing PCC thickness, in Revised Procedure, MOR = 0 psi Revised Procedure, MOR = 00 psi CDOT, MOR = 0 psi CDOT, MOR = 00 psi 0 0 0,000 00,000,000,000 0,000,000 ESALs b.) -ft (. m) joint spacing. NOTE: in =. mm; ft = 0. m; psi =. kpa Figure. PCC design thickness with respect to PCC MOR. Modulus of subgrade reaction None of the design procedures are very sensitive to the modulus of subgrade reaction. This would be as expected since the load is carried through the HMA layer for these thin overlays. The interface bonding between the HMA layer and the PCC layer creates a composite system. TRB 0 Annual Meeting

14 When the pavement structure behaves as a composite system, the PCC layer is structurally most sensitive to the HMA layer and, as a composite system, is less sensitive to the k-value. This is why the predicted thicknesses were found to be very sensitive to the thickness of the HMA layer. Sensitivity studies for both the ACPA and CDOT procedures also recognized this lack of sensitivity to the modulus of subgrade reaction. CONCLUSIONS The revised procedure for bonded whitetopping includes four primary revisions to the PCA and CDOT procedures that have been traditionally used:.) the failure mode is dictated by the joint spacing and not the overlay thickness;.) the stress adjustments factors have been more extensively calibrated;.) equivalent gradients to be used as the design input are defined based on the pavement structure and geographical location of the project and.) the change in HMA stiffness with changes in temperature is considered. The revised procedure provides reasonable overlay thicknesses. This is based on comparisons made between the predicted performance and the actual performance for four separate projects. It was also found that the predicted thickness obtained using the revised procedure was sensitive to HMA thickness, the level of traffic and the MOR of the PCC as would be expected. The PCA and CDOT procedures have served well for many years. These revisions help to improve the capabilities of these procedures and provide a more user-friendly interface. Further calibration of the stress adjustment factors should be performed as additional performance data becomes. Until then, this revised procedure is a second generation design procedure that can be used for the design of bonded whitetopping overlays in lieu of the original PCA and CDOT design procedures. ACKNOWLEDGMENTS The authors would like to thank the Minnesota, Missouri, Mississippi, New York, Pennsylvania, and Texas Departments of Transportation. These states are all participating in the FHWA Pooled Fund Study TPF - under which this work was performed. REFERENCES () Wu, C.L., S.M. Tarr, T.M. Refai, M.A. Nagai, and M.J. Sheehan. Development of Ultra- Thin Whitetopping Design Procedure. Report RD. Portland Cement Association, Skokie, IL,. () Concrete Overlay on Asphalt (BCOA) Thickness Designer. American Concrete Pavements Association. Rosemont, IL. Accessed August, 0. () Tarr, S.M., M.J. Sheehan, and P. A. Okamoto. Guidelines for the Thickness Design of Bonded Whitetopping Pavement in the State of Colorado. Report No. CDOTDTD- R-- 0. Colorado. Department of Transportation, Denver, CO, December. () Sheehan, M.J., S.M. Tarr, and S. Tayabji. Instrumentation and Field Testing of Thin Whitetopping Pavement in Colorado and Revision of the Existing Colorado Thin Whitetopping Procedure. Report No. CDOT DTD-R-00-. Colorado Department of Transportation, Denver, CO, August 00. () Barman, M., J. M. Vandenbossche, F. Mu and K. Gatti. Task report: Development of a Rational Mechanistic-Empirical Based Design Guide for Thin and Ultra-Thin Whitetopping. University of Pittsburgh. 00. TRB 0 Annual Meeting

15 0 () Larson, G. and B. Dempsey. EICM Software. Enhanced Integrated Climatic Model Version.0 (EICM). University of Illinois, Urbana, IL. 00. () Mu, F. and J.M. Vandenbossche, Establishing Effective Linear Temperature Gradients for Bonded Concrete Overlays on Asphalt Pavements. Transportation Research Record: Journal of the Transportation Research Board, Transportation Research Board of the National Academies, Washington, D.C., 0. (In press). () Barman, M., F. Mu and J.M. Vandenbossche. Development of a Rational Mechanistic- Empirical Based Design Guide for Thin and Ultrathin Whitetopping, Task : Climatic Considerations. Federal Highway Administration (FHWA) Pooled Fund study, TPF -, 0, p -. () Vandenbossche, J.M. Performance Analysis of Ultra-thin Whitetopping Intersections on US-, Elk River, Minnesota. Transportation Research Record: Journal of the Transportation Research Board, No., Transportation Research Board of the National Academics, Washington, D.C., 00, pp. -. TRB 0 Annual Meeting