2010 FAA Worldwide Airport Technology Conference Atlantic City, New Jersey April 20 – April 22

2 Analysis and Design of Airfield Pavements Using Laboratory Tests and Mechanistic – Empirical Methodology Lorina Popescu, P.E., UCPRC Rita Leahy, P.E., APACA Carl Monismith, P.E., UCPRC

3 Outline  Introduction  Establish mix design criteria for taxiways using Simple Shear Test  Estimate permanent deformation using laboratory tests and M-E methodology  Airfield pavement design example using long-life performance concepts  Construction considerations & concluding notes

4 Introduction  SHRP developed tests Simple Shear Test (AASHTO T-320, ASTM D- 7312) RSST-CH Flexural Fatigue Test (AASHTO T-321, ASTM D- 7460)  SHRP tests and new analysis methods adapted to evaluate HMA performance with large commercial aircraft loading

5 Establish Mix Design Criteria for Taxiways Using the Simple Shear Test

6 San Francisco International Airport Project outline  Distresses observed shoving and rutting in AC turn areas of taxiway - slow moving and sharp turning rutting distortions (dimpling) under static loading  Different trial mixes to mitigate rutting problem  Cores extracted from distressed areas

7 San Francisco International Airport Project outline  AC mixes in full compliance with FAA mix design  Enhancements to FAA mix design to reduce observed rutting  High Stability mix  SHRP Simple Shear Test primary tool used to evaluate mix rutting performance

8 Simple Shear Test (SST)  Evaluate the permanent deformation characteristics of FMFC cores;

9 Simple Shear Test (SST)  Sample size: D=6 in, H=2 in;  Shear stress: 10 psi (69kPa)  Loading time 0.1 sec; 0.6 sec rest period;  Test temperature 122F (50C);

10 RSST-CH Permanent Deformation Analysis  Typical permanent shear strain and load cycles relationship:  p = a*N b N = number of cycles to 5% shear strain

11 RSST test results on field extracted cores

12 Binder content selection

13 Notes  Stiffness alone is not sufficient for mix design  Repeated loading used to arrive at design binder content

14 Estimate Permanent Deformation Using Laboratory Tests and M-E Methodology

15 Estimate rutting performance - NDIA project outlook  New Doha International Airport – due to open July 2011;  All HMA TW/RW  Built partially on reclaimed land;  Two parallel runways;  40 gate terminal;

16 NDIA project outlook Environment - Desert  Avg temperature – > 40C (104F) May - Sep  Avg Annual Rainfall – 70mm (2¾ in) Oct - Mar

17 NDIA Project outlook  Typical aircraft loading 51,250 to 56,000 lb/tire  Tire pressure 215 to 220 lb/in 2

18 Rutting Susceptibility Laboratory Tests  Hamburg Wheel Tracking Device Captures the combined effects of rutting and moisture damage; Mixture was both moisture and rut resistant

19 Rutting Susceptibility Laboratory Tests  RSST-CH Asphalt content: optimum & optimum “+” for sensitivity analysis 122F (50C) 5000 load cycles;

20 Rutting Susceptibility Laboratory Tests  Shear Frequency Sweep test data Asphalt content:optimum & optimum “+” 3 temperatures (4C, 20C and 46C); 3 frequencies (0.1Hz, 1Hz and 10Hz);  Develop master curve to determine shear modulus with temperature and loading rate.

21 Performance tests results

22 Rutting Susceptibility Mechanistic Empirical Approach  Mechanistic approach to determine the accumulation of plastic strain;  Rutting in AC is assumed to be controlled by shear deformation;  Time hardening principle applied to calculate cumulative plastic strain due to shear deformation;   i = f(,  e,N)

23 Rutting Susceptibility Mechanistic Empirical Approach  Shell subgrade strain criterion to estimate contribution to deformation from base and subgrade;

24 Rutting Susceptibility Mechanistic Empirical Approach  Analysis assumptions: Aircraft operations uniformly distributed throughout the year; Plastic strain accumulated during the warmest months; Plastic strain accumulated 8 hrs/day; 50% of aircraft operations at max. weight No aircraft wander;

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26 Notes  RSST-CH test helped identify the target binder content and the construction control limits (±0.25%)

27 Airfield Pavement Design Example Using Long-Life Highway Design Concepts

28 Pavement Structural Section Design for Wide-Bodied Aircraft  Lab test data from I-710, LA County – Long Life Performance concept; Carries traffic into and out of the Port of Long Beach; ADT = 155,000 vehicles/day; 13% trucks;

29 Pavement Structural Section Design for Wide-Bodied Aircraft  Use of ME procedure Multilayer elastic program Laboratory flexural fatigue and stiffness data

30 Estimate Elastic Modulus and Fatigue Life Elastic Modulus  PBA-6a*: E (ln stif) = *Temp  PG 64-16: E (ln stif) = *AV *AC *Temp Fatigue Life  PG 64-16: E (ln nf) = *AV *lnstn

31 Analysis – Pavement Structure 4 in PBA-6a*(PG64-40), 4.7% AC, 6% AV, E = f(Temp) 12 inches AB (TBD) PG 64-16, 4.7% AC, 6% AV E=f(AV, AC, Temp) 3 in PG RB, 5.2% AC, 3% AV E = f(AV, AC, Temp) SG

32 Data Analysis Factorial  Three wide-bodied aircraft types: Boeing Airbus Boeing  Design to strain levels at the bottom of the HMA layer: ~100, 200, 300 s

33 Data Analysis Factorial  Two climate zones: Desert area – Yuma, AZ Coastal region – San Francisco, CA  Temperature: Aug (hotter month) Jan (Yuma), Feb (SF) – colder month  Temperature at 1 in depth increments – EICM to determine layer stiffness for ME analysis

34 Yuma: Tensile Strain vs. Asphalt Layer Thickness

35 Check Fatigue Resistance for 25in Asphalt Thickness  25in asphalt layer thickness: Aug: Avg  t = 180 s, Nf=5*10 7 Jan: Avg  t = 105 s, Nf=7*10 8  20 years: 5*10 6 operations 1.25*10 6 operations over 4 warmer months 3.75*10 6 operations over 8 cooler months

36 Check Fatigue Resistance for 25in Asphalt Thickness  Apply linear summation of cycle ratio cumulative damage hypothesis – Miner criteria  Shell subgrade strain criteria  v =2.8*10-2*N-0.25

37 Construction Considerations

38 Construction Considerations  NDIA project RSST-CH tests suggested tighter binder content tolerances  ±0.25% asphalt binder content

39 Influence of As-Constructed Asphalt Content on Rutting Performance

40 Construction Considerations  Long Life Performance project AV 4% - 6% rut-resistant upper and intermediate HMA layer; Desirable AV <=3% - rich bottom layer  Increased fatigue life – key for long life performance Tack coat essential between lifts

41 Concluding Notes  Shear Test was useful for : HMA design Establishing performance criteria under repeated trafficking on taxiways  Examine materials response at more than one binder content – more effective use of different quantities of binder (rich bottom concept)

42 Concluding Notes  Potential savings: More effective use of materials Ability to estimate long term performance

THANK YOU!