2010 FAA Worldwide Airport Technology Conference Atlantic City, New Jersey April 20 – April 22 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 2 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 3 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 4 Establish Mix Design Criteria for Taxiways Using the Simple Shear Test 5 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 6 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 7 Simple Shear Test (SST) Evaluate the permanent deformation characteristics of FMFC cores; 8 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); 9 RSST test results on field extracted cores 10,000,000 High Stability Mixes 1,000,000 AR 8000 Mixes Repetitions to 5 % Shear Strain 100,000 95% reliability 10,000 (5% probability of failure) 1,000 80% 50% 100 10% 10 1 0 2 4 6 8 10 12 Air-Void Content 11 Binder content selection 1.0E+06 Repetitions to 5 percent shear strain (log) 1.0E+05 N = 100,000 at 80 % Each point is the average of 3 test 1.0E+04 results Design asphalt / binder content 1.0E+03 Asphalt content (percent) 12 Notes Stiffness alone is not sufficient for mix design Repeated loading used to arrive at design binder content 13 Estimate Permanent Deformation Using Laboratory Tests and M-E Methodology 14 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; 15 NDIA project outlook Environment - Desert Avg temperature – > 40C (104F) May - Sep Avg Annual Rainfall – 70mm (2¾ in) Oct - Mar 16 NDIA Project outlook Typical aircraft loading 51,250 to 56,000 lb/tire Tire pressure 215 to 220 lb/in2 17 Rutting Susceptibility Laboratory Tests Hamburg Wheel Tracking Device Captures the combined effects of rutting and moisture damage; Mixture was both moisture and rut resistant 18 Rutting Susceptibility Laboratory Tests RSST-CH Asphalt content: optimum & optimum “+” for sensitivity analysis 122F (50C) 5000 load cycles; 19 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. 20 Performance tests results Optimum Optimum Plus Optimum Optimum Plus 10000 3.0 2 Permanent Shear Strain, % 2.5 Dynamic Modulus, k/in 1000 2.0 1.5 100 1.0 0.5 10 1.0E-06 1.0E-03 1.0E+00 1.0E+03 1.0E+06 0.0 0 1000 2000 3000 4000 5000 Reduced Frequency, Hz (20C Reference Temp) Load Cycle 21 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; gi = f(t, ge,N) 22 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; 24 Accumulation of Inelastic/Plastic Strain "Optimum" and "Optimum + 0.5% Mixes" 0.35 Inelastic/Plastic Strain 0.30 0.25 Cumulative 0.20 0.15 0.10 0.05 0.00 0 300 600 900 1200 1500 Number of days (5yrs x 244 days/yr) 25 Cumulative inelastic strain AC optimum Cumulative inelastic strain Opt + 0.5% Notes RSST-CH test helped identify the target binder content and the construction control limits (±0.25%) 26 Airfield Pavement Design Example Using Long-Life Highway Design Concepts 27 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; 28 Pavement Structural Section Design for Wide-Bodied Aircraft Use of ME procedure Multilayer elastic program Laboratory flexural fatigue and stiffness data 29 Estimate Elastic Modulus and Fatigue Life Elastic Modulus PBA-6a*: E (ln stif) = 9.1116- 0.1137*Temp PG 64-16: E (ln stif) = 14.6459- 0.1708*AV-0.8032*AC-0.0549*Temp Fatigue Life PG 64-16: E (ln nf) = -36.5184-0.6470*AV- 6.5315*lnstn 30 Analysis – Pavement Structure 4 in PBA-6a*(PG64-40), 4.7% AC, 6% AV, E = f(Temp) (TBD) PG 64-16, 4.7% AC, 6% AV E=f(AV, AC, Temp) 3 in PG 64-16 RB, 5.2% AC, 3% AV E = f(AV, AC, Temp) 12 inches AB SG 31 Data Analysis Factorial Three wide-bodied aircraft types: Boeing 747-400 Airbus 380-800 Boeing 777-800 Design to strain levels at the bottom of the HMA layer: ~100, 200, 300 ms 32 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 33 Yuma: Tensile Strain vs. Asphalt Layer Thickness 1000 Tensile strain (HMA bottom) (microstrain) 100 10 1 10 15 20 25 30 35 40 Total AC Thickness (in) Yuma Aug-B777 Yuma Aug - B747 Yuma Aug - A380 Yuma Jan - B777 Yuma Jan - B747 Yuma Jan - A380 34 Check Fatigue Resistance for 25in Asphalt Thickness 25in asphalt layer thickness: Aug: Avg et = 180 ms, Nf=5*107 Jan: Avg et = 105 ms, Nf=7*108 20 years: 5*106 operations 1.25*106 operations over 4 warmer months 3.75*106 operations over 8 cooler months 35 Check Fatigue Resistance for 25in Asphalt Thickness Apply linear summation of cycle ratio cumulative damage hypothesis – Miner criteria Shell subgrade strain criteria ev=2.8*10-2*N-0.25 36 Construction Considerations 37 Construction Considerations NDIA project RSST-CH tests suggested tighter binder content tolerances ±0.25% asphalt binder content 38 Influence of As-Constructed Asphalt Content on Rutting Performance 4.00 As- constructed Simulated ESALs to 10% rutting (15mm or more rut depth) expressed as fraction of target ESALs standard 3.50 deviation of asphalt content (%) 3.00 0.114 2.50 0.19 0.266 2.00 1.50 1.00 0.50 0.00 4.4 4.6 4.8 5 5.2 5.4 As-constructed average asphalt content (%) 39 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 40 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) 41 Concluding Notes Potential savings: More effective use of materials Ability to estimate long term performance 42 THANK YOU!
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