CREEP AND REPEATED CREEP-RECOVERY AS RUTTING PERFORMANCE TESTS FOR AIRPORT HMA MIX DESIGN

Transcription

1 CREEP AND REPEATED CREEP-RECOVERY AS RUTTING PERFORMANCE TESTS FOR AIRPORT HMA MIX DESIGN John F. Rushing (corresponding author) U.S. Army Engineer Research and Development Center CEERD-GM-A 0 Halls Ferry Road Vicksburg, MS 0- Phone: (0) - Fax: (0) John.F.Rushing@usace.army.mil Dallas N. Little, Ph.D. Texas A&M University CE/TTI 0 TAMU College Station, TX - Phone: () - Fax: () - d-little@tamu.edu Original Submission: August, 0,0 Words, Figures (0 words), Tables (,00 words) = 0 Total Equivalent Words Paper Prepared for Consideration for Presentation and Publication at the nd Annual Meeting of the Transportation Research Board TRB 0 Annual Meeting

2 John F. Rushing and Dallas N. Little ABSTRACT A performance test to evaluate rutting susceptibility is needed to accompany current volumetric property requirements of airport hot mix asphalt (HMA) designed using a Superpave Gyratory Compactor. The new performance test will provide a level of confidence that pavement constructed using a selected HMA mixture will function according to its design. This paper presents results from a laboratory study to identify a performance test for accepting hot asphalt mixtures for constructing airport pavements designed for high tire pressure traffic. Performance tests intended to indicate rutting susceptibility were performed on twenty-six HMA mixtures. Twenty-two of these mixtures met all aggregate and volumetric property requirements for airport pavement construction; the remaining four mixtures were designed with excessive percentage of natural sand (0%) as rut-susceptible mixtures. Results from asphalt pavement analyzer, triaxial creep, and triaxial repeated creep-recovery tests are presented. Statistical analyses performed on the results indicate the rate of increase in permanent strain and the flow time value determined from triaxial creep testing provide the strongest correlation to Asphalt Pavement Analyzer (APA) simulated traffic rutting. INTRODUCTION Rutting is a primary load-related distress in airport pavements subjected to high tire pressure and aircraft gear loads. Hot mix asphalt (HMA) for airport pavements has historically been designed using materials and compaction requirements that can withstand these loading conditions. Historically, the Marshall design procedure has been used by the Federal Aviation Administration (FAA) for airport pavement (). The design procedure includes meeting aggregate and binder requirements along with laboratory mixture design volumetric requirements to produce acceptable mixtures. Marshall stability and flow test values provide an empirical, threshold metric to help insure a stable mixture under traffic, but this empirical test cannot truly assess performance. Performance can be assessed by either a damage model based on sophisticated testing of engineering and material properties or tests that mimic the traffic loads encountered in the field. A new mixture design procedure being implemented by the FAA allows the use of the Superpave Gyratory Compactor (SGC) in lieu of Marshall impact compaction to compact specimens during the mixture design process (). This new procedure includes the same aggregate, binder, and volumetric requirements as those that are currently part of the Marshall protocol, but no performance test is included in the new protocol. Studies are currently being conducted to identify a companion performance test for the new mixture design procedures, but one has not yet been adopted. NCHRP Project - recommended creep and repeated creep-recovery tests as destructive indicators of asphalt mixture performance along with the non-destructive dynamic modulus test (). Flow time and flow number parameters are commonly extracted from creep and creep-recovery tests, respectively. Both parameters have demonstrated a promising correlation with field performance (-). Test conditions for creep and repeated creep-recovery are typically 0- to 0- psi (- to -kpa) load with - to 0- psi (-to 0-kPa) confinement (). These stress levels are commensurate with highway traffic loads. Aircraft tire pressures commonly exceed 00 psi (0 kpa) for commercial airliners and can reach as high as psi (0 kpa) for military fighter aircraft. The high pressures exerted by such traffic warrant modification of testing parameters to better represent actual traffic. Ahlrich performed repeated creep-recovery tests TRB 0 Annual Meeting

3 John F. Rushing and Dallas N. Little using an axial stress of 00 psi (0 kpa) with a confining stress of 0 psi ( kpa) to assess the influence of aggregate properties on rutting performance of airfield HMA (). Cooley et al. performed similar tests using axial stress levels of 00, 00, and 0 psi (0, 0, and kpa) with 0 psi ( kpa) confinement (0). The axial stress and confinement selected for this study were 00 and 0 psi (0 and kpa), respectively. The objective of this study was to evaluate the ability of creep and repeated creeprecovery tests to serve as a performance test to assess the potential for rutting under high tire pressure aircraft in the design phase of hot asphalt mixtures. HMA mixtures selected on the basis of their ability to represent a wide range in rutting potential were included in the study. The ability of the creep and repeated creep-recovery tests to differentiate among these mixtures and their applicability as a mixture design and/or quality assurance test were investigated. The field rutting susceptibility of the mixtures tested under field conditions was not evaluated. Results from asphalt pavement analyzer tests were used in lieu of field tests for relative rutting comparisons. Mixture Designs and Specimen Properties Twenty-six asphalt concrete mixtures were included in the study. A neat PG - asphalt binder obtained from Ergon Asphalt and Emulsions, Inc., was used in each mixture. Aggregates used in this study consisted of material stockpiles collected for a previous study which evaluated the use of the SGC for airport asphalt mixture design (). These aggregates included limestone, granite, and crushed chert gravel. Coarse and fine gradations, with respect to the allowable FAA gradation, are included in the study. The mixtures designed using these aggregates are described by Rushing et al. () in a previous study investigating high-pressure APA testing. All mixtures were designed using seventy gyrations as recommended for N design for HMA mixtures designed for high tire pressure aircraft (), but this is currently being evaluated by the FAA. The design or optimum binder content was selected to produce.% air voids. Specimens produced for creep and repeated creep-recovery testing were compacted to N design using the design binder content at a target height of. in. (0 mm). Mixture mass was proportioned so that the compacted specimen height would be near the target value. Specimens for creep and repeated creep-recovery testing were cored using a -in.- (0-mm-) diameter core saw to remove the center portion of the specimen. The ends of the specimens were then cut using a circular saw so that the specimen height was in. (0 mm) and the ends were parallel. Table shows the aggregate types, maximum size, relative gradation, the percentage of uncrushed natural sand, and the design binder content for mixtures included in this study. The mixture designation used to identify these mixtures in this paper is also given. 0 TRB 0 Annual Meeting

4 John F. Rushing and Dallas N. Little TABLE Mixture Properties. Aggregate Type Maximum Aggregate Size Gradation Percentage of Mortar Sand Design Binder Content Mixture Designation Granite ½ in. Fine 0. / FGN 0. / FGN0 0. / FGN0 Coarse 0. / CGN 0. / CGN0 0. / CGN0 ¾ in. Fine 0. / FGN 0. / FGN0 0 / FGN0 Coarse 0. / CGN 0. / CGN0 0. / CGN0 Limestone ½ in. Fine 0. / FLS Chert Gravel 0. / FLS0 Coarse 0. / CLS 0 / CLS0 ¾ in. Fine 0. / FLS 0. / FLS0 Coarse 0. / CLS 0. / CLS0 ½ in. Center 0. / FGV 0. / FGV0 ¾ in. Fine 0. / FGV 0. / FGV0 Coarse 0. / CGV 0. / CGV0 LABORATORY TESTS Results from APA, creep, and repeated creep-recovery laboratory performance tests are presented in this paper. The average results from two replicates are given. In addition, one representative mix was selected for testing twelve replicates using each test procedure. These results were used to identify the coefficient of variation of each test. The following sections describe each test method used in this study. TRB 0 Annual Meeting

5 John F. Rushing and Dallas N. Little 0 0 Asphalt Pavement Analyzer (APA) The APA configuration used in this study was designed specifically to simulate high tire pressures associated with aircraft. An APA tube or hose pressure of 0 psi ( kpa) under a wheel load of 0 lb ( N) was used for testing. The test temperature was o F ( o C) as was the high temperature PG grade for the binder used in all mixtures. Cylindrical asphalt concrete specimens with a target air void content of.% were prepared and tested. The air void content was selected as the midpoint of the allowable range in the FAA mixture design procedure. Two replicate specimens were tested for each mixture. The APA reports the average rut depth of the two specimens. Thirty-three mixtures were included in the study. Each mixture was comprised of one neat binder and three aggregate types. Some mixtures included natural sand. Cyclic loads were applied by the APA at a rate of one cycle per second. The terminal rut depth of the specimens was set at 0. in. ( mm) after,000 cycles; however, the test was terminated when the 0.-in.- (-mm-) rut depth was achieved if this occurred before,000 cycles. Once one of the two specimens reached terminal rut depth, the test was stopped. However, since the APA reports the average rut depth for the two specimens, some average rut depths were less than 0. in. ( mm). Creep The static creep triaxial test measures permanent deformation as a function of time when a constant load is applied to a cylindrical HMA specimen. Cumulative permanent deformation is reported as a function of time during loading. Cumulative permanent deformation has historically been categorized for a wide range of materials--such as metals, polymers and some composites--into three zones: primary, secondary, and tertiary, as indicated on the representative creep data set (Figure ). The primary zone is characterized by a decreasing rate of accumulated permanent deformation during specimen densification. In the secondary zone, permanent strain accumulates in a relatively linear fashion. The tertiary zone occurs as the specimen fails and is characterized by an increasing rate of accumulated permanent deformation. TRB 0 Annual Meeting

6 Permanent Axial Strain (%) John F. Rushing and Dallas N. Little Primary Secondary Tertiary Time (seconds) FIGURE Representative creep data. 0 0 NCHRP report provides a procedure for measuring the flow time of HMA using static creep tests (). The procedure is based on application of creep loads on unconfined or confined cylindrical specimens, which are in. (00 mm- in diameter and in. (0 mm) in height and cored from gyratory compacted mixtures. The stress conditions are determined by the engineer. The basic principles related to the creep test as stipulated in NCHRP report for flow time testing were applied in this study. Variations in stress conditions and test temperatures were considered in order to apply more directly to airport pavements. The confined test was selected in lieu of the unconfined compression test because it better simulates field conditions. Specifically a confining stress of 0 psi ( kpa) and a deviator stress of 00 psi (0 kpa) were selected. The test temperature was selected to be the mean monthly pavement temperature (MMPT) as defined by Witczak (). An MMPT of 0 o F ( o C) was used for Vicksburg, Mississippi, the selected climate. The flow time (FT) is defined as the time corresponding to the minimal rate of change of permanent axial strain during the static creep test (Figure a). The FT for each specimen was determined by fitting a second order polynomial to a narrower range of the data in Figure a and solving the regression equation for the point when the rate of change in permanent strain is a minimum (Figure b). TRB 0 Annual Meeting

7 Rate of Change in Permanent Strain Permanent Strain Slope John F. Rushing and Dallas N. Little Polynomial Curve Fitting Region Time (seconds) a) Rate of change in permanent strain FT = 0 y =.E-0x -.E-0x +.E Time (seconds) b) Determination of flow time TRB 0 Annual Meeting

8 Permanent Axial Strain (%) Permanent Axial Strain (%) John F. Rushing and Dallas N. Little Tertiary Flow Value (TF) Slope of Secondary Flow Region 0 Slope of Tertiary Flow Region Time (seconds) c) Procedure for determining tertiary flow value TF = FT = Time (seconds) d) Flow time and tertiary flow value FIGURE Determining rutting parameters for creep data. TRB 0 Annual Meeting

9 John F. Rushing and Dallas N. Little 0 The FT for each mixture occurred near the beginning of the secondary flow region for the set of testing conditions previously defined. These data were also analyzed to determine the number of load cycles at which tertiary flow begins. A graphical procedure was used to determine this point. First, a line was drawn along the slope of the secondary flow region. Next, a line was drawn following the slope of the tertiary flow region. The intercept of these lines is defined to be the tertiary flow value (TF) for these data. Figure c illustrates the procedure for defining the TF value. Figure d shows an example of the FT (indicated by a star) and the TF (indicated by a triangle) values along a typical data curve. The secondary phase of the creep compliance curve can be graphically shown using power models in the form listed in equation. D = D(t) D o = a*t m () where D = viscoelastic compliance at any time D(t) = total compliance at any time D o = instantaneous compliance t = loading time a, m = material regression coefficients 0 Figure shows test data plotted on a log-log scale. The slope, m, and the intercept, a, are noted on the figure. The slope and intercept values for each specimen were determined by fitting repeated creep-recovery data to Equation. Typically, decreasing m and increasing a will improve resistance to permanent deformation (). TRB 0 Annual Meeting

10 log D(t) John F. Rushing and Dallas N. Little 0 Slope "m" Intercept "a" D(t) = at m Log Time (seconds) FIGURE Slope and intercept determination. 0 0 Repeated Creep-Recovery The repeated creep recovery triaxial test measures permanent deformation as a function of number of axial load cycles applied to a cylindrical HMA specimen. The repeated creep recovery test is used to determine the flow number for HMA in the asphalt mixture performance tester (AMPT) according to AASHTO TP -0. The procedure allows one to perform the test on an unconfined or confined cylindrical specimen, in. (00 mm) in diameter by in. (0 mm) in height and cored from gyratory compacted mixtures. The stress conditions are determined by the engineer. The basic principles of the NCHRP -recommended flow number test were used in this study (). A loading period of 0.s along with a dwell time of 0.s comprised the load pulse. A confining stress of 0 psi ( kpa) and deviator stress of 00 psi (0 kpa) were selected. The test temperature was 0 o F ( o C). The flow number (FN) is defined as the number of load cycles corresponding to the minimal rate of change of permanent axial strain during the repeated creep-recovery test. The FN for each specimen was determined by fitting a second order polynomial to a narrower range of the data and solving the regression equation for the point when the rate of change in permanent strain is a minimum, using the same procedure applied to creep test data. Similar to the FT, the FN for each mixture occurred near the beginning of the secondary flow region in all cases for this set of testing conditions. The data were further analyzed to determine the number of load cycles where tertiary flow begins. The previously described procedure was used to determine the tertiary flow value. TRB 0 Annual Meeting

11 John F. Rushing and Dallas N. Little 0 The rate of accumulated permanent deformation can be mathematically expressed using the classic power-law model in equation. The data from the repeated creep-recovery test were fitted to equation to determine the material regression coefficients, a and b. In general, resistance to permanent deformation increases as a increases and b decreases (). ε p = a*n b () 0 where ε p = permanent strain N = number of load cycles a, b = material regression coefficient TEST RESULTS Tables through present a summary of rutting test data. Although the APA tests were performed to,000 cycles, many specimens failed prematurely by exceeding a -mm rutting threshold. Rushing et al. () recommended preliminary criterion based on,000 cycles when testing at 0 psi ( kpa) hose pressure and 0 lb ( N) load. The APA rut depth after,000 cycles is presented in Table. Some mixtures exceeded 0. in. ( mm) rutting after,000 cycles. The approximate rut depth at,000 cycles was extrapolated from available data for these mixtures. Mixtures containing 0% natural sand failed by,00 cycles, so approximated rut depths after,000 cycles could not be accurately determined. The actual field rutting susceptibility of these mixtures is not known; however, the mixture ranking seems reasonable based on the aggregate properties and historical empirical data. The results from the APA test were used in lieu of field data for comparing the rutting susceptibility as measured by the creep and repeated creep-recovery tests. Four parameters are reported for both the creep and repeated creep-recovery test. These parameters include the values of the slope and intercept for the secondary rutting region of the data plotted on a log-log scale, as well as the values corresponding to the FT or FN and the tertiary flow value. These values are presented in Tables and. Table provides a numerical ranking of the mixture rutting performance as indicated by APA rut depth at,000 cycles as well as the creep and repeated creep recovery parameters. As indicated by the mixture ranking for the different parameters, results from creep and the repeated creep-recovery test do provide a reasonable indication of mixture rutting susceptibility. The parameter that ranks mixtures similarly to the APA test is the intercept value from the secondary flow region for both tests. Table also provides the coefficient of variation for each performance test parameter. The value presented was determined from twelve replicates of one representative mix. The coefficient of variation was 0% for the APA. This statistic for creep and creep-recovery tests varied depending on the parameter. The a and m values from the creep test had the lowest coefficients of variation at, and %, respectively. Other coefficients of variation for the test parameters ranged from % to %. The slope and intercept parameters determined using the power law model had lower coefficients of variation than the flow time/number or tertiary flow values for both the creep and repeated creep-recovery tests. TRB 0 Annual Meeting

12 John F. Rushing and Dallas N. Little Three statistical methods were used to identify the strength of the correlation between the APA rut depth and the eight parameters investigated from creep and repeated creep-recovery tests. All methods were performed using SigmaStat statistical software. The data for mixtures containing 0 percent natural sand were not included in the calculations because the APA rut depth values would have been inexact. The results from these methods are presented in Table. First, the R value was determined. The R value is a measure of how well the regression line approximates the real data points. R values can range from 0 to, with larger values indicating less variability between the regression line and the actual data points. Next, a Pearson s correlation coefficient was determined. The Pearson s correlation coefficient is a measure of the linear dependence between two x and y variables and has a numerical range from - to. A Pearson coefficient of means that two variables are perfectly correlated; a value of - means that two variables are perfectly inverse. A value of 0 indicates no correlation. Finally, a Spearman s rank order correlation was determined. The Spearman s rank order correlation is a non-parametric measure of dependence between two variables. The Spearman test defines its correlation coefficient between ranked variables. A numerical ranking of the order of the data set replaces the actual test values, and the analysis is performed on the assigned rank value. Similar to the Pearson test, the Spearman test assigns a correlation coefficient ranging from - to. The relationship between Spearman coefficient and correlation are the same as described for the Pearson test. The Spearman correlation is less sensitive to outliers that are in the tails of the data set. The test parameter indicating the greatest correlation to APA rut depth was the slope of the secondary flow region in the creep test. This degree of correlation for this test parameter was somewhat higher than the correlation for all other test parameters, according to all three analysis methods. The test parameter indicating the poorest correlation to APA rut depth was the intercept of the secondary flow region of the repeated creep-recovery test. The statistical analysis methods indicate almost no correlation of this parameter to APA rut depth. The intercept of the secondary flow region of the creep test also had a very low correlation to APA rut depth. The correlations of the FT or FN and the tertiary flow value for their respective tests were almost identical, indicating that either of these values is equally appropriate for determining a mixture s rutting susceptibility. The FT and the tertiary flow value from the creep test had a stronger correlation than the FN and the tertiary flow value from the repeated creep-recovery test, according to all three analysis methods. The slope of the secondary flow region of the repeated creep-recovery test had a poor R value of 0., and a relatively poor Pearson coefficient of 0.. The higher Spearman correlation of 0. indicates the parameter is better at ranking the mixtures than at actually predicting the outcomes based on numerical test values 0 TRB 0 Annual Meeting

13 John F. Rushing and Dallas N. Little TABLE APA Results (Rut Depth at,000 Cycles) Rut Depth Rut Depth MIX ID (mm) MIX ID (mm) / CGN. / CGN0. / CGN0 0. / CGN0 -- a / CGN0 -- a / CGV. b / CLS. / CGV0. / CLS0.0 / CLS. / FGN. / CLS0.0 / FGN0. b / FGN. / FGN0 -- a / FGN0. / FLS. / FGN0 -- a / FLS0. / FGV. b / GV b / FGV0. b / GV0 b / FLS. / CGN. / FLS0. a Data could not be determined due to specimen failure before,00 cycles. b Data extrapolated because specimens failed before,000 cycles 0 TRB 0 Annual Meeting

14 John F. Rushing and Dallas N. Little TABLE Measured Creep Test Parameters Mixture a m FT TF / FGN / CGN / FGN / CGN / FGN / CGN / FGN / CGN / FGN0 0.. / CGN / FGN / CGN0 0.. / GV / FGV / CGV / GV / FGV / CGV / FLS / CLS / FLS / CLS / FLS / CLS / FLS / CLS TRB 0 Annual Meeting

15 John F. Rushing and Dallas N. Little TABLE Measured Repeated Creep-Recovery Test Parameters Mixture a b FN TF / FGN / CGN / FGN / CGN / FGN / CGN / FGN / CGN / FGN / CGN / FGN / CGN / GV / FGV / CGV / GV / FGV / CGV / FLS / CLS / FLS / CLS / FLS / CLS / FLS / CLS TRB 0 Annual Meeting

16 John F. Rushing and Dallas N. Little TABLE Mixture Ranking APA Flow Time Flow Number Mixture a m FT TF a b FN TF / FLS0 0 / CLS 0 / FGN0 0 / FLS / CLS 0 / FLS / CLS / FGN 0 / FGN / CGN0 0 / FLS0 0 / CGN / CLS0 0 0 / CGN / CGV0 / CGN0 / FGV0 0 / CGV 0 0 / FGN0 / FGV 0 0 / GV 0 / GV0 / CGN0 / FGN0 / CGN0 / FGN0 Coefficient of Variation (%) 0 0 TABLE Statistical Groupings Pearson Correlation Coefficient Performance Test Parameters R Creep a m FT TF Repeated Creep- Recovery a b FN TF Does not include 0% sand mixtures Spearman Rank Order Correlation TRB 0 Annual Meeting

17 John F. Rushing and Dallas N. Little CONCLUSIONS There is a pressing need for a performance test to accompany HMA mixture design for airport pavements. Although the Marshall design method uses an empirical index test, a new design method using the SGC relies only on volumetric properties of the compacted mixture for acceptance. This study investigated the suitability of creep and repeated creep-recovery tests as a mixture design performance test for accepting HMA mixtures for use on airport pavements subjected to high tire pressure aircraft. From this study the following are concluded: 0 0 The most significant factor influencing permanent deformation is excessive natural sand (0%). Mixtures containing excessive natural sand achieved tertiary flow in fewer than 0 seconds during the creep test and in fewer than 0 cycles of the repeated creeprecovery test. Although mixtures met all aggregate property and volumetric requirements, the performance test results indicate large differences in rutting susceptibility. All parameters investigated, except for the intercept values of the creep and the repeated creep-recovery tests, ranked mixtures containing excessive natural sand as the poorest performers. The slope of the secondary flow region in the creep test correlated most strongly with APA results according to the coefficient of determination, R, the Pearson correlation coefficient, and the Spearman rank order correlation. The two methods used to define tertiary flow (flow time/number and tertiary flow value) produced the same correlation with APA rut depth. The two methods resulted in very similar mixture performance rankings. The correlation between APA rut depth and FT was better than the correlation between APA rut depth and FN. 0 0 RECOMMENDATIONS Based on the results of this study, the m and FT parameters determined from creep tests using a 00 psi (0 kpa) axial stress with 0 psi ( kpa) confinement produce a reasonable indication of asphalt mixture rut resistance. The creep test should be further investigated as a mixture performance test for accepting HMA for high tire pressure aircraft during mixture design. This recommendation is limited to the materials used in this study. Further testing should include additional binder types, specifically modified binders. Further, mixtures with proven successful field performance should be evaluated, along with mixtures that have shown to rut easily. A criterion based on the relationship between laboratory and field performance should be developed for accepting a mixture. ACKNOWLEDGEMENTS The study described in this paper was supported by the FAA Airport Technology Research and Development Branch under the FAA-ERDC Interagency Agreement. The authors would like to thank Mr. Tim McCaffrey, Mr. Kevin Taylor and Mr. Lance Warnock of the U.S. Army Engineer Research and Development Center for their efforts with the specimen preparation and laboratory testing. The contents of the paper reflect the views of the authors, who are responsible for the facts and accuracy of the data presented within. The contents do not necessarily reflect the official views and policies of the FAA. The paper does not constitute a TRB 0 Annual Meeting

18 John F. Rushing and Dallas N. Little standard, specification, or regulation. Permission to publish was granted by Director, Geotechnical and Structures Laboratory REFERENCES. Standards for Specifying Construction of Airports. Advisory Circular 0/0 0 E, U.S. Department of Transportation, Federal Aviation Administration, 00.. Item P-0 Plant Mix Bituminous Pavements (Superpave). Engineering Brief No. A, U.S. Department of Transportation, Federal Aviation Administration, 00.. Witczak, M. W., K. Kaloush, T. Peillinen, M.E. Basyouny, and H. Von Quintus. NCHRP Report : Simple Performance Test for Superpave Mix Design. Transportation Research Board, National Research Council, Washington, D.C., 00.. Brown, E.R., P.S. Kandhal, and J. Zhang. Performance Testing for Hot Mix Asphalt. NCAT report -0, November 00.. Roberts, F.L., P.S. Kandhal, E.R. Brown, D.-Y. Lee, and T.W. Kennedy. Hot Mix Asphalt Materials, Mixture Design and Construction. nd ed. NAPA Education Foundation, Lanham, MD,.. Bhasin, A., J.W. Button, and A. Chowdhury Evaluation of Simple Performance Tests on Hot- Mix Asphalt Mixtures from South Central United States. In Transportation Research Record: Journal of the Transportation Research Board, No., Transportation Research Board of the National Academies, Washington, D.C., 00, pp. -.. Kaloush, K. E., M. W. Witczak, R. Roque, S. Brown, J. D Angelo, M. Marasteanu, and E. Masad. Tertiary Flow Characteristics of Asphalt Mixtures. Journal of Association of Asphalt Paving Technologists, Vol., 00, pp Zhang, J., E.R. Brown, P.S. Kandhal, and R. West, An Overview of Fundamental and Simulative Performance Tests for Hot Mix Asphalt. Journal of ASTM International, Vol., No., 00, pp. -.. Ahlrich, R.C. Influence of Aggregate Gradation and Particle Shape/Texture on Permanent Deformation of Hot Mix Asphalt Pavements. Technical Report GL--. U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS,. 0. Cooley, L.A. Jr., R.C. Ahlrich, R.S. James, B.D. Prowell, and E.R. Brown. Implementation of Superpave Mix Design for Airfield Pavements. AAPTP 0-0. Auburn, AL, 00.. Rushing, J.F., Development of Criteria for Using the Superpave Gyratory Compactor to Design Airport Pavement Mixtures. Master s Thesis. Mississippi State University, Mississippi State, MS, 00.. Rushing, J. F., D. N. Little, and N. Garg. Using the Asphalt Pavement Analyzer to Assess Rutting Susceptibility of HMA Designed for High Tire Pressure Aircraft. Transportation Research Record XXXX, Transportation Research Board of the National Academies, Washington, D.C., 0, pp. XX-XX (In press).. Witczak, M. W. Simplified Approach to Determine the Annual Pavement Temperature Distribution. Work Element Environmental Effects Mode, Tech Memo. University of Maryland, College Park,.. Leahy, R. B. Permanent Deformation Characteristics of Asphalt Concrete. Ph.D. Dissertation, University of Maryland,. TRB 0 Annual Meeting