Complete Testing Suite for HMA Performance Prediction

Transcription

1 Complete Testing Suite for HMA Performance Prediction Presenter: Imad L. Al-Qadi, PhD, PE, Dist.M.ASCE H. Ozer, P. Singhvi, J. Rivera, A. El Khatib, M. Mueller, and J. Trepanier,

2 Loaded Flexible Pavement Direction of Travel Aggregate Base Deflection Free Water Wedge Subgrade Deflection Hydrostatic Pressure 2

3 Pavement Distresses Segregation due to paver operation Heavy traffic Aging and thermal loads Source: Nunn and Ferne (2001) 3

4 Rutting/ Cracking in HMA 4

5 Flexible Pavement System Material Characterization Asphalt concrete Granular Materials Materials Long-Lasting Pavement Recycled Material RAP, RAS, REOB Pavement Structure Rolling Resistance Roughness, Texture, Def., Heat Exchange Sustainability 5

6 Contribution of Asphalt Binder An analysis of over 1000 mixes shows increased energy with increased binder % Transportation Other Materials Binder (40-91%)

7 Contribution of Asphalt Binder An analysis of over 1000 mixes shows increased energy with increased binder % Asphalt Binder Replacement Transportation Other Materials (ABR) Recycled Asphalt Pavement Binder (40-91%) Recycled Asphalt Shingles

8 Relative Energy & GWP Illinois Center for Transportation Environmental Savings from ABR Virgin mix SMA mix SMA mix 60% ABR MIX: 20% Energy Savings Energy GHG %ABR 22% CO 2 Savings Yang et al. (2014). Environmental impacts from producing asphalt mixtures with varying degrees of recycled asphalt materials.

9 Challenges with RAP/RAS (ABR) Fatigue cracking issue: stiffer mixes with high ABR may exhibit early fatigue cracking Thermal/Block cracking issue: Stiffer mixes have reduced relaxation potential Shingle asphalt is air blown to harden asphalt (PG ) then additional aging on the roofs RAP AC can be hard or soft depends on project(s) milled Counteracting binder selection of virgin binder becomes arbitrary

10 Low Temperature Cracking Fatigue/Block/Other Forms of Cracking Permanent Deformation -40 C -20 C 20 C 40 C Superpave Volumetrics Rut Test Cracking Test

11 Pavement Cracking Traffic loading, temperature, AC material properties all play a role VERY COMPLEX We can t afford running a battery of tests to simulate these conditions SUCH TESTS DO NOT EVEN EXIST We need a simple, affordable (money AND time), and meaningful test as a best approximate to overall cracking related damage THERMAL, FATIGUE, BLOCK,

12 IL-SCB Test Modified SCB fracture test conducted at 25 C LVDT control load 50 mm/min Parameters calculated: Fracture energy (G f ) Peak load (P max ) & corresponding displacement (u o ) Critical displacement (u 1 ) Slope at inflection point (m)

13 E*, ksi Illinois Center for Transportation SCB Simulations Perform numerical simulations of SCB test with bulk characteristic from complex modulus tests CZ Element Master Curve 10 1.E-06 1.E-04 1.E-02 1.E+00 1.E+02 1.E+04 Loading Frequency, Hz Duplicate Nodes Bulk Properties from Complex Modulus Test Fracture Properties Using Cohesive Zone Model

14 Load Illinois Center for Transportation FEM Results FEM simulations of SMA with 25% ABR N80-25 T = 25 C Experimental mm/min Numerical mm/min Experimental - 50mm/min Numerical - 50mm/min Where 3 Excellence 4 and Transportation Meet CMOD (mm)

15 DIC: Full Field Measurements

16 eyy FPZ (Temperature Effect) 25 C 0%RAS (64-22) -12 C 7%RAS (64-22) 5mm

17 Fracture Energy Ambiguities

18 Development of Flexibility Index Flexibility Index (FI) = G F 1 abs(m)

19 Applicability and Seamless Implementation

20 Applicability and Implementation Can use AASHTO T-283 (TSR) equipment Two low-cost prototypes were already manufactured (9-18K)

21 Conditioning Method Water bath conditioning allows the use of AASHTO T-283 (TSR) set up

22 IL-SCB Tool A software tool was developed to process IL-SCB results

23 Provide a Significant and Meaningful Spread in Test Output

24 Case Study: High ABR Mixes Goal: Identify a difference in the performance of: Mix ABR Binder Constant Properties L4 0% AC (%): 6 L7 20% L9 30% L10 60% VMA (%): 15.3 Expected Behavior Increment in ABR Decreases Toughness

25 Probability Density Illinois Center for Transportation Low Temperature SCB (-12ºC): SCB (-12ºC, 1 mm/min, CMOD Control) ABR 0% vs 20% 0.02 L4 μ = 742 σ = 57 μ = 795 σ = 22 Overlap: 43% 0.01 L Fracture Energy (J/m2)

26 Probability Density Illinois Center for Transportation Low Temperature SCB (-12ºC): 0.02 SCB (-12ºC, 1 mm/min, CMOD Control) ABR 20% vs 30% Overlap: 11% 0.01 L7 L9 μ = 677 σ = 55 μ = 795 σ = Fracture Energy (J/m2)

27 Probability Density Illinois Center for Transportation Low Temperature SCB (-12ºC): 0.02 SCB (-12ºC, 1 mm/min, CMOD Control) ABR L4 30% vs 60% 0.01 L7 L9 μ = 677 σ = 55 Overlap: 58% L10 μ = 635 σ = Fracture Energy (J/m2)

28 Low Temperature SCB: High Repeatability: ~ 9% COV Normal Distribution Overlap: Low Discrimination: 40% Overlap 30 % 40%

29 Probability Density Illinois Center for Transportation Intermediate Temperature SCB (25 ºC): ABR 0% vs 20% L4 SCB (25ºC, 50 mm/min) μ = 1622 σ = 51 μ = 1895 σ = 73 Overlap: 3% L Fracture Energy (J/m 2 )

30 Probability Density Illinois Center for Transportation Intermediate Temperature SCB (25 ºC): ABR 20% vs 30% Overlap: 37% L7 L9 SCB (25ºC, 50 mm/min) μ = 1622 σ = 51 μ = 1703 σ = Fracture Energy (J/m 2 )

31 Probability Density Illinois Center for Transportation Intermediate Temperature SCB (25 ºC): ABR 30% vs 60% Overlap: 21% L4 L7 L9 L10 SCB (25ºC, 50 mm/min) μ = 1280 σ = 164 μ = 1703 σ = Fracture Energy (J/m 2 )

32 Intermediate Temperature SCB: Intermediate Repeatability: ~ 10% COV Normal Distribution Overlap: Intermediate Discrimination: ~ 25% Overlap 30 % 40%

33 Probability Distribution Illinois Center for Transportation Flexibility Index SCB (25 ºC): Overlaps: < 3% SCB (25ºC, 50 mm/min) Increase in ABR = Reduction in FI 60% 30% 20% 0% L4 L7 L9 L Flexibility Index

34 Flexibility Index SCB (25 ºC): Reduced Repeatability: ~ 15% COV Normal Distribution Overlap: High Discrimination: ~ 3% Overlap 30 % 40%

35 Correlation to Field Performance

36 Accelerated Loading Facility Simulates truck traffic with controlled loading and pavement temperatures. Up to 35,000 cycles can be applied per week. Wheel load can be varied from 33 kn (7,500 lb) representing a light truck to 84 kn (19,000 lb) simulating a heavy axle.

37 Lane Properties ABR Group Lane WMA Binder Grade Control 1 - PG % (w/ RAP) 40% (RAP) 20% (w/ RAS) 9 Water PG Chemical PG PG Chemical PG PG PG PG64-22

38 IL-SCB vs. Fatigue Cracking

39 Field Cores Field cores were obtained from nine IDOT districts Flexibility index values were compared to field performance data obtained from districts

40 Field Correlation (D1) District 1 Section # Field Perf. FI Thickness (mm) 5 Bad Bad Bad Good Bad Bad Good Bad Good Good Good Bad Good Increasing FI

41 Effect of Construction Year

42 Flexibility Index Illinois Center for Transportation Balanced Mix Stiff & FLEXIBLE SOFT & FLEXIBLE Stiff & Brittle Unstable Rut Depth Maximum Allowable Passes

43 Flexibility Index Illinois Center for Transportation Balanced Mix High Performance Stiff & FLEXIBLE SOFT & FLEXIBLE Stiff & Brittle Unstable Rut Depth Maximum Allowable Passes

44 Final Remarks Asphalt mixture brittleness can result from mixture volumetrics as well as adding recycled materials (RAP and RAS) Low temperature fracture tests could not distinguish between AC mixes IL-SCB test is a practical, affordable, and reliable test to distinguish between mixes cracking resistance The method is supported by extensive lab and field testing, theoretical, and numerical methods, and DIC technique

45 Findings and Remarks IL-SCB test method and the proposed Flexibility Index have successfully screened hundreds of AC mixes for changes in brittleness Implementation of a balanced mix design and field performance validation is underway Simple interaction plots combining Hamburg and IL- SCB tests A life-cycle approach is needed to assess sustainability impact of recycled materials Pavement performance and traffic volumes are critical

46 Acknowledgements ICT R Project Technical Review Panel Undergrad and graduate students involved ICT research engineers ICT.illinois.edu

47 HMA Testing Book Ends HARD SOFT HMA Courtesy of David Lippert