Constitutive Modeling of Asphalt Concrete: A Multiscale Perspective

Transcription

1 Constitutive Modeling of Asphalt Concrete: A Multiscale Perspective Shane Underwood Assistant Professor School of Sustainability and the Built Environment Civil, Environmental, and Sustainable Engineering Program ITE Student Chapter Seminar October 9, 2012

2 Outline 2 Objective Motivation Background Macroscale constitutive model for fatigue in asphalt concrete Bridging characteristic length scales in asphalt concrete materials Scale-up to structural performance assessment Closing

3 Objective To describe how constitutive models in combination with a multiscale approach can be of use in the asphalt concrete and asphalt pavement field. 3

4 Resource Competition Economic System Definition Motivation Sustainability and Resiliency Multipurpose Applications New Materials Operations/ Maintenance Technical Knowledge Design Paradigms 4 Unified Analysis and Modeling Methodology

5 Multiscale Modeling as a Unifying Concept Molecular Range Materials Range Engineering Range Chromotography, AFM, DSC DMA, Rheology, Viscoelasticity, Viscoplasticity, Continuum Damage Mechanics, Fracture Mechanics Loading, Environmental, Structure Binder Mastic FAM Mix Molecular Simulation Molecular Dynamics Microstructural Models Empirical Models Empirical Models Phenomenological Models Analy. Suspension Models Discrete Element Models Empirical Models Mech.-Empirical Models Finite Element Models

6 Background Performance modeling is the process of predicting how well a material or structure will perform in-service, e.g., classic performance laws 1 K N K f B N p 1 B 6

7 Constitutive Model A mathematical function that relates stress and strain. E 7

8 MACROSCALE MODELING: CONSTITUTIVE MODELING THE FATIGUE PROCESS IN ASPHALT CONCRETE

9 Peak-to-Peak Strain (m ) Constitutive Material Model Fatigue in Asphalt Concrete 1.E+03 1.E+02 9 Mix 1 Mix 2 Best Fit, Mix 1 Best Fit, Mix 2 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 Number of Cycles to Failure

10 Constitutive Material Model Continuum Damage Mechanics,, E = C C 10 Under load damage is observed as a reduction in stiffness thus the key function is the relationship between damage, S, and material stiffness, C

11 Constitutive Material Model Continuum Damage Mechanics Viscoelastic Continuum Damage (VECD) Model Elastic-Viscoelastic Correspondence Principle Continuum Damage Mechanics Time-Temperature Superposition with Growing Damage Linear viscoelastic effects Microcracking related strength/stiffness degradation Joint time/rate- Temperature effects 11

12 E* (MPa) Baseline Pavement Response , E Control CRTB SBS Terpolymer 1.E-08 1.E-05 1.E-02 1.E+01 1.E+04 Reduced Frequency (5C)

13 C Damage Characteristic Curve ,, Monotonic-Fast Monotonic-Slow CX-High CX-Low CS0-High CS0-Low 0.2 E = C E+00 1E+05 2E+05 3E+05 4E+05 S

14 Strain Amplitude Prediction of Fatigue Relationship C Measured 19C Measured 27C Measured Predicted E+01 1.E+03 1.E+05 1.E Nf (Cycle) *Hou et al. (2010). Fatigue Perf. Pred. of NC Mixtures using the S-VECD Model, AAPT, 79

15 Testing Requirement Conventional Fatigue Approach Constitutive Model Approach Temperature: 3 Load amplitude: 3 Mode of loading: 2 Replicates: 3 LVE characterization Cyclic test at 2 levels and 1 temperature Replicates: E* - 3 Cyclic tests (2 months) 7 tests (3 days) 15

16 Strain Amplitude (m ) Rank Sustainable Material Evaluation Lowered Production Temperature Mixtures Recycled Asphalt Pavement Mixtures 16 1.E+03 1.E+02 HMA Dry HMA Moisture WMA Dry WMA Moisture 1.E+01 1.E+02 1.E+04 1.E+06 1.E+08 N f 70-80% Difference in N f 0-20% Difference in N f *Experimental work completed by Mr. Jongsub Lee and Mr. Tian Hou S9.5B S9.5C S12.5C I19.0B I19.0C B25.0B Use of RAP Materials

17 Thermal Cracking Evaluation 17 *Chehab et al.. (2005). VEPCD Model Application to Thermal Cracking of AC, JMCE, 17(4)

18 Limits of Macro-Level Constitutive Models Many of these phenomena are directly related to mechanisms at the local scale, which multiscale models account for directly. Source: Rozeveld et al

19 MULTISCALE MODELING: LINKING MECHANICAL BEHAVIORS ACROSS MATERIAL LENGTH SCALES

20 Upscaling Constitutive Behaviors Molecular Range Materials Range Engineering Range Particles smaller than mm Particles smaller than mm Particles smaller than mm Binder Mastic FAM Mix Characteristic Length Scale (meters)

21 Primary Research Questions How do the different material phases exist within the mixture? What are the constitutive behaviors of individual material phases? Sieved Ignition Digital Microscopy Scanning Electron Microscopy (SEM) Meso-Gravimetric and SEM How do the individual phases interact to yield the observed behaviors of the complete composite? High Concentration Mastic 21 Rheological Liquid Very Low Concentration Mastic Low Concentration Mastic FAM Mix

22 Macro Assembly Post Mixing Post Ignition (no disturbance) 22 22

23 Macro Assembly #200 Sized #100 Sized #100 Sized #200 Sized Filler #50 Sized Large Filler #200 Sized Agglomerations of Filler

24 Micro Assembly Scanning Electron Microscope Mix Failure Surface V filler = 20% V filler = 30% V filler = 40%

25 Passing (%) Meso-Sampling for Microstructural Study FAM Coarse Particle Image Analysis and 2-D to 3-D Distribution Algorithm Known Gradation SEM Calibration SEM Verification 1 SEM Verification Sieve Size.45 (mm)

26 Microstructural Study S9.5B I19.0C Vfiller in Mastic (%) Coarse Avg. FAM Avg. Vol. Avg. Vfiller in Mastic (%) FAM Avg. Vol Avg. 0 0 Coarse Samples FAM Samples FAM Samples 26

27 G* (Pa) Multiscale Characteristics 1.E+09 1.E+07 1.E+05 Mix FAM 27 Mastic Binder 1.E+03 1.E-06 1.E-04 1.E-02 1.E+00 1.E+02 1.E+04 Reduced Angular Frequency (rad/s) *Underwood and Kim (2011). Experimental Investigation into the Multiscale Behavior of Asphalt Concrete, IJPE, Special Multiscale Modeling Issue, 12(4).

28 C Multiscale Characteristics Binder Mastic Mix S

29 G* (Pa) C Upscaling Constitutive Behaviors Mastic to Mixture Experiments characterize aggregate and mastic. Constitutive behaviors of mixture are then predicted from analytical model. 1.E Predicted Measured E C 40C 54C 1.E+06 1.E-01 1.E+00 1.E+01 1.E+02 1.E Frequency (rad/s) S

30 Performance Based Mix Design Macroscale Constitutive Model Approach Multiscale Approach Effect of AC Content: x4 AV Contents at single AC: x3 Gradation: x2 Binder LVE Mastic LVE: x5 FAM or Mix LVE: x2 Void Content Tests 24 mixes (3 months) 18 mechanical tests 2-6 void content tests (7 days) 30

31 Multiple Replicates C.... Multiple Replicates Multiple Replicates.. % Passing Scale n Scale n-1 Scale 1 Upscaling with Computational Methods 2D Gradation. Sieve Size Scale (n) Scale (n-1) Scale (1) Prony Series n E n E i n i Output From Scale (n) Component i m n n n n i E () t E E i e i 1 t Input to Scale (n-1) Output from Scale (n-1). Input to Scale (1) S x 10 7 ZHANG P, (2003). Microstructure generation of asphalt concrete and lattice modeling of its cracking behavior under low temperature 31 Theses and Dissertations, NCSU. Thanks to Arash Banadaki for the slide contents

32 MULTISCALE MODELING: STRUCTURAL ANALYSIS

33 Mechanistic-Empirical Paradigm Inputs Structure Materials Traffic Climate Layered Analysis (,, d) Performance Assessment D ijk N N ijk f K 1 N ijk 1 K 2 M J K Damage D Accumulation i 1 j 1 k 1 D i jk Distress Accumulation Crack C log 1 C2 D e 33

34 Mechanistic Paradigm Inputs Structure Materials Traffic Climate Pavement Analysis Engine (,, d) Pavement Response E R Damage Accumulation C R Distress Accumulation Crack fcn S 34

35 Multiscale Mechanistic Paradigm Binder Mastic FAM Mix Characteristic Length Scale (meters) 35

36 Pavement Evaluation Response Modeling Winter Summer 36

37 Pavement Fatigue Life Prediction log Predicted Nf SBS Control CRTB Terpolymer y = x R 2 = log Field N f

38 Damage Area (%) Damage Area (%) Damage Area (%) Damage Area (%) Assessment of Design Alternatives BB3 BB1 Aggregate cm 40 cm cm 18 cm 28 cm 0 8 cm 18 cm 28 cm Base Layer Thickness Base Layer Thickness Subgrade Antifrost ASTM PMA cm 18 cm 28 cm Base Layer Thickness 0 A2 A5 A8 A10 A11 A12 A13 A14 A15 Test Section

39 Molecular Range How do molecular components form and interact to yield behaviors of asphalt? What properties should I specify for asphalt binder materials? Materials Range How do engineering materials assemble and interact to yield behaviors of asphalt concrete? How should the available materials be assembled (designed)? Engineering Range How does asphalt concrete interact within a structure and environmental condition to prescribed loading? What materials should I specify for an asphalt concrete pavement? 39 Multiscale Analysis and Modeling

40 Thank You