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Dr. Haleh Azari AASHTO Advanced Pavement Research Laboratory (AAPRL) Permanent Deformation Characterization Using Incremental Repeated Load Permanent Deformation.

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Presentation on theme: "Dr. Haleh Azari AASHTO Advanced Pavement Research Laboratory (AAPRL) Permanent Deformation Characterization Using Incremental Repeated Load Permanent Deformation."— Presentation transcript:

1 Dr. Haleh Azari AASHTO Advanced Pavement Research Laboratory (AAPRL) Permanent Deformation Characterization Using Incremental Repeated Load Permanent Deformation Test (iRLPD) NEAUPG Steering Committee Meeting March

2 RLPD Test Protocol Background A flow number test protocol was developed during NCHRP 9-19, which was later, refined during NCHRP 9-29 (AASHTO TP 79) Several parameters were left undetermined and not standardized FHWA ETG has created a task force to ▫standardize the variables of the test such as test temperature, stress level, confinement ▫Establish criteria that can reliably discriminate between various mixtures

3 Selection of Promising RLPD Protocols Different agencies have offered different approaches in standardizing the flow number test Six promising approaches were selected by the ETG Flow Number Task Force for further evaluation Selected methods are proposed by AAT (NCHRP 9-33), NCAT, Van Quintus (NCHRP 9-30A), MTE, AAPRL, UNR Nine different mixtures representing a wide range of traffic and climate were provided by the state DOTs and industries for the evaluation AAPRL is testing the nine materials according to five of the proposed methods UNR is testing the materials according to UNR proposed method

4 Mix. # MixtureTrafficBinder GradeMixture NMAS, mmSupplier LTPPBind High Temperature, 50% Reliability, °C 1WI (E3)<3PG Erv Dukatz – MTE Const NCPG Todd Whittington NC DOT TXPG Dale Rand - TXDOT WI (E10)<10PG Erv Dukatz –Mathy Const INPG Huber FLPG Jim Musselman - FLDOT NJ>30PG Tom Bennert NJDOT AL (NCAT track sec. PG Randy West CAPG Adam Hand 62.5 List of Materials and Suppliers

5 Description of Test Protocols NCHRP9-30A, MTE, NCAT, NCHRP9-33 approaches are according to conventional flow no. test: ▫Test continuous until either material goes to flow, 10,000 cycles is completed, or 50,000 microstrain of total permanent deformation is reached ▫Tests are conducted on 3 replicates at one temperature and one stress level ▫MTE method is conducted on 9 replicates at 1 temperature and three stress levels (each three replicates tested at one stress level) AAPRL method (iRLPD) uses 3 replicates; each specimen is tested incrementally at different stress levels 5

6 MethodsNCHRP 9-33NCATNCHRP 9-30AMTEAAPRL (iRLPD) Confinement, kPa (psi)069 (10 ) Deviatoric Stress, kPa (psi) 600 (87)482.6 (70) 400, 600, 800 (58, 87, 116) 400, 600, 800 (58, 87, 116) Mix. #MaterialTemperature, °C* 1 WI (E3) NC TX WI (E10) IN FL NJ AL CA Stresses and Temperatures *Temperatures are selected based on 50 % reliability high pavement temperature from LTPPBind at depth of 20 mm

7 Description of Incremental RLPD (iRLPD) Test iRLPD test is conducted at one temperature (LTPPBind High Temperature, 50% Reliability) in four increments ▫1000 cycles at 100 kPa (to ensure primary stage of deformation is completed and mixture is in the secondary stage of deformation) ▫500 cycles at 400 kPa ▫500 cycles at 600 kPa ▫500 cycles at 800 kPa ▫Total of 2500 cycles takes 43 min. iRLPD method uses strain rate at the end of each increment (minimum strain rate=MSR) as the measure of resistance of a mixture to permanent deformation 7

8 RLPD Parameters Strain rate consistent Primary Secondary Tertiary Flow Number Minimum Strain rate Graphs of strain and strain rate versus number of cycles Consist of three portions : Primary, secondary, and tertiary No. of Cycles Output of Conventional Flow No. Test

9 Example of iRLPD Test, Increasing Temperature 9

10 Example of iRLPD Test, Increasing Stress 10

11 MSR vs. Temperature and Stress For combinations of stress and temperature the same MSR values were observed It was found out that effect of temperature and stress are interchangeable Parameter TP, which is the product of temperature and stress is then used to explain MSR 11

12 Create MSR Master Curve Plot MSR as a Function of Temperature * Pressure (TP) MSR master curve MSR master curve defines the response of a mixture at any temperature and stress 12

13 MSR Threshold Values Criteria for selecting stress and temperature was based on achieving MSR values in the range of 1 to 30 microstrain/cycle:  A combination of temperature and stress that results in MSR of less than 1 microstrain/cycle indicates that the mixture has the potential to stand much higher temperature and stresses  A combination of temperature and stress that results in MSR value higher than 30 microstrain/cycle indicates that the mixture is reaching its limit in resisting flow 13

14 MSR Threshold Values ▫A combination of temperature and stress that results in MSR of less than 1 microstrain/cycle indicates that the mixture has the potential to stand much higher temperature and stresses ▫A combination of temperature and stress that results in MSR value higher than 30 microstrain/cycle indicates that the mixture is reaching its limit in resisting flow ▫Selected the stress levels to obtain MSR values greater than 1 μstrain/cycle and smaller than 30 μstrain/cycle 14

15 MSR Curves for WI (E3), WI(E10), NC, IN

16 MSR Master Curves for AL,TX, FL, CA

17 17 MSR Values from iRLPD and Flow No. Tests WI(E10), WI(E3), FL, CA

18 MSR Values from iRLPD and Flow No. IN, NC, TX,AL 18

19 Ranking of Mixtures based on MSR Master curve 19

20 Field Applications, Estimate Rut Depth 20 Use traffic and pavement temperature data to determine TP (temperature * pressure) Obtain MSR from the master curve for the determined TP Multiply MSR (strain /cycle) by traffic ESAL to obtain total strain Multiply strain by pavement thickness to estimate rut depth

21 Example, Estimate Rut depth MSR= a e b*TP Material 1Material 2Material 3Material 4Material 5 a b High Pavement Temperature Pressure (MPa)0.6 Axles, millions1033 MSR, μstrain/cycle micron/axle Axles 1st Year Rut 1st yr, mm Rut 20 years, mm Thick75 Years20 Months4 (ratio 0.33) Hours8 (ratio 0.33) Wander0.5 Aging Ratio0.5

22 Field Applications, Determine Traffic Level from MSR 22 ▫Use traffic and temperature data to determine TP (temperature * pressure) ▫Obtain MSR from the master curve for the determined TP ▫Multiply MSR (strain /cycle) by layer thickness to obtain permanent deformation/cycle ▫Divide maximum allowable rut depth by deformation/cycle to obtain the allowable no. of passes (ESALS)

23 Example, Determine Traffic Level from MSR Material 1Material 2Material 3Material 4 MSR Terminal Rut12.7 micron/axle Rut 1st yr6.35 Axles 1st Year2,4048,01324,03840,064 With Wander4,80816,02648,07780,128 Allowable Axles, 20 yrs865,3852,884,6158,653,84614,423, Thick75 Years20 Months4 (ratio 0.33) Hours8 (ratio 0.33) Wander0.5 Aging Ratio0.5

24 Field Applications, Determine Acceptable MSR Value for A Design Traffic Level 24 ▫Divide allowable rut depth by Design ESAL to calculate allowable permanent deformation per axel ▫Divide allowable permanent deformation by design thickness to obtain strain per axel or MSR

25 Determine Acceptable MSR Values for Ranges of Design Traffic Levels Axles1,000,0003,000,00010,000,00030,000,00050,000,000 Terminal Rut12.5 Rut 1st yr6.25 Axles5,55616,66755,556166,667277,778 Axles w/ wander2,7788,33327,77883,333138,889 micron/axle MSR Thick75 Years20 Months4 (ratio 0.33) Hours8 (ratio 0.33) Wander0.5 Aging Ratio0.5

26 Table 1-Ranges of MSR values for various Traffic levels 26 Axels MSR, strain/cycle <3,000,000 >10 & <30 3,000,000 to 10,000,000>3 & <10 10,000,000 to 30,000,000 >1 & < 3 >50,000,000<1

27 Laboratory Application: Ranking of Mixtures 27 Two ways of ranking/ grading mixtures in laboratory (for a fixed stress and pavement temperature and no consideration of design ESALS): ▫For a particular TP value, e.g., 36 (0.6 MPa * 60 ° C), the lower the MSR, the more resistance to rutting ▫For a particular MSR value, e.g., 25, the higher the TP, the more resistance to rutting

28 Laboratory Application: Mixture Selection 28 If for a determined TP, MSR value of a mixture is less than the values provided in Table 1, the mixture meets the criteria for high temperature performance Determine TP using: ▫50 % reliability high pavement temperature from LTPPBind at depth of 20 mm ▫Average tire pressure of 600 kPa (90 psi)

29 Selection of Mixtures, Example 29 High pavement temperature for Region 1 from LTPPBind= 62.7C Use stress of 600 kPa (0.6 Mpa) TP= 62.7 * 0.6= 37.6 MPa ° C MSR from master curve= 12.5 (> 10 & <30) Mixture is acceptable for design traffic of less 3 million (see Table 1)

30 Summary, Comparison of iRLPD with Conventional Flow Test 30 MSR values from conventional flow number test coincided with the MSR master curve produced from iRLPD test iRLPD test using 3 replicates provides the same MSR values as conventional flow number test using 9 replicates While conventional flow number test produces one MSR value, iRLPD test produces a sweep of MSR values for creating MSR master curve

31 31 Using incremental RLPD, testing time is reduced by a factor of 4 Test takes less than 45 min for each replicate Complete high temperature characterization of a mixture in 2 hr. and 15 min (3 replicates) Minimum strain rate values have much smaller variability than flow no. or total permanent strain (average CV of 7 % vs. 13%) MSR values from MSR master curve are directly applied to the field without use of transfer functions Summary, Comparison Cont.

32 Summary of Differences between Conventional Flow No. and iRLPD Tests 32 Test Parameters Incremental RLPDConventional Flow No. Test Test propertyMinimum Strain Rate (MSR) Number of Cycles to Flow, minimum strain rate (MSR), total permanent strain No. of cycles1000, 500, 500, 500variable Test temperature 50 % reliability high pavement temperature from LTPPBind at depth of 20 mm Not defined Stress levelFour stress levels: 100, 400, 600, 800 kPa (15, 58, 87, 116 psi)Not defined Test durationLess than 45 minutes Variable- few minutes to 3 hrs depending on temperature, stress level, and resistance of the material Test output produces a sweep of MSR values for creating MSR master curveproduces one MSR, one flow number, one total permanent strain Test VariabilityMSR has small variability Both flow no and total permanent strain are highly variable Field application Test results can be directly applied to the field without transfer function Flow number has not been directly applied to the field Laboratory application Test results are applied for mixture selection and mixture gradingNo mixture selection/mixture ranking methodology exists based on flow no. test results

33 Summary, Laboratory Application of MSR Master Curve Mixture selection: ▫For a particular TP (pavement temperature * average pressure) and design traffic level, a mixture with MSR values within the ranges provided in Table 1 is acceptable in terms of high temperature performance Ranking/grading of various mixtures: ▫For a fixed TP, a mixture with lower MSR is more resistant to permanent deformation ▫For a fixed MSR, a mixture with higher TP is more resistant to permanent deformation 33

34 Summary, Field Application of MSR Master Curve MSR (strain per cycle) from MSR master curve can be used to estimate : ▫Allowable traffic ESALs ▫Total rut depth The design traffic ESAL can be used to calculate acceptable MSR (Table 1) 34

35 Recommendations:  Evaluate the applicability of Incremental RLPD for WMA, and high percentage RAP, and combination of both  Investigate Incremental RLPD test method for different confinement stresses 35

36 Thank you. Questions?


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