SUPERPAVE PERFORMANCE GRADED BINDER TESTS. Superpave Performance Graded Binder Tests 1

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1 SUPERPAVE PERFORMANCE GRADED BINDER TESTS Superpave Performance Graded Binder Tests 1

2 PG Specifications Fundamental properties related to pavement performance Environmental factors In-service & construction temperatures Short and long term aging Superpave Performance Graded Binder Tests 2

3 PG Specifications Based on rheological testing Rheology: study of flow and deformation Asphalt cement is a viscoelastic material Behavior depends on: Temperature Time of loading Aging (properties change with time) Superpave Performance Graded Binder Tests 3

4 High Temperature Behavior High in-service temperature Desert climates Summer temperatures Sustained loads Slow moving trucks Intersections Viscous Liquid Superpave Performance Graded Binder Tests 4

5 Pavement Behavior (Warm Temperatures) Permanent deformation (rutting) Mixture is plastic Depends on asphalt source, additives, and aggregate properties Superpave Performance Graded Binder Tests 5

6 Permanent Deformation Courtesy of FHWA Function of warm weather and traffic Superpave Performance Graded Binder Tests 6

7 Low Temperature Behavior Low temperature Cold climates Winter Rapid loads Fast moving trucks Elastic Solid Hooke s Law σ = τ E Superpave Performance Graded Binder Tests 7

8 Pavement Behavior (Low Temperatures) Thermal cracks Stress generated by contraction due to drop in temperature Crack forms when thermal stresses exceed ability of material to relieve stress through deformation Material is brittle Depends on source of asphalt and aggregate properties Superpave Performance Graded Binder Tests 8

9 Thermal Cracking Courtesy of FHWA Superpave Performance Graded Binder Tests 9

10 Aging Asphalt reacts with oxygen oxidative or age hardening Short term Volatilization of specific components During construction process Long term Over life of pavement (in-service) Superpave Performance Graded Binder Tests 10

11 Superpave Asphalt Binder Specification The grading system is based on climate PG Performance Grade Min pavement temperature Average 7-day max pavement temperature Superpave Performance Graded Binder Tests 11

12 Pavement Temperatures are Calculated Calculated by Superpave software High temperature 20 mm below the surface of mixture Low temperature At surface of mixture Pave temp = f (air temp, depth, latitude) Superpave Performance Graded Binder Tests 12

13 Tests Used in PG Specifications Construction RV DSR BBR Superpave Performance Graded Binder Tests 13

14 Concentric Cylinder Rheometers Concentric Cylinder τ Rθ = Mi i 2 π R i2 L γ = Ω R R o -R i Superpave Performance Graded Binder Tests 14

15 Rotational Viscometer Torque Motor Thermosel Environmental Chamber Inner Cylinder Digital Temperature Controller Superpave Performance Graded Binder Tests 15

16 Original Properties, Rutting, and Fatigue DSR RV BBR Superpave Performance Graded Binder Tests 16

17 Dynamic Shear Rheometer (DSR) Parallel Plate Shear flow varies with gap height and radius Non-homogeneous flow τ R = 2 M π R 3 γ R = R Θ Superpave Performance Graded Binder Tests 17 h

18 Oscillating Plate B A C Fixed Plate A B A C Time Test operates at 10 rad/sec or 1.59 Hz 360 o = 2 π radians per circle 1 rad = 57.3 o 1 cycle Superpave Performance Graded Binder Tests 18

19 Elastic Viscous B A A Strain Time C Strain in-phase δ = 0 o Strain out-of-phase δ = 90 o Superpave Performance Graded Binder Tests 19

20 Complex Modulus, G* Viscous Modulus, G δ Storage Modulus, G Complex Modulus is the vector sum of the storage and viscous modulus Superpave Performance Graded Binder Tests 20

21 DSR Equipment DSR Equipment Computer Control and Data Acquisition Superpave Performance Graded Binder Tests 21

22 Motor Parallel Plates with Sample Area for Liquid Bath Superpave Performance Graded Binder Tests 22

23 25 mm Plate with Sample Superpave Performance Graded Binder Tests 23

24 Rutting RV BBR DSR Superpave Performance Graded Binder Tests 24

25 Permanent Deformation Addressed by: G*/sin δ on unaged binder > 1.00 kpa G*/sin δ on RTFO aged binder > 2.20 kpa For the early part of the service life Superpave Performance Graded Binder Tests 25

26 Short Term Binder Aging Rolling Thin Film Oven Simulates aging from hot mixing and construction Superpave Performance Graded Binder Tests 26

27 Inside of RTFO Fan Rotating Bottle Carriage Air Line Superpave Performance Graded Binder Tests 27

28 Bottles Before and After Testing Opening in Bottle Superpave Performance Graded Binder Tests 28

29 Testing Calculate mass loss after RTFO Mass loss, % = Original mass - Aged mass Original mass x 100 Determine G*/sin δ for RTFO aged material at same test temp. used for original asphalt cement Superpave Performance Graded Binder Tests 29

30 Permanent Deformation Question: Why a minimum G*/sin δ to address rutting? Answer: We want a stiff, elastic binder to contribute to mix rutting resistance How: By increasing G* or decreasing δ Superpave Performance Graded Binder Tests 30

31 Fatigue RV DSR BBR Superpave Performance Graded Binder Tests 31

32 Fatigue Cracking Function of repeated traffic loads over time (in wheel paths) Superpave Performance Graded Binder Tests 32

33 Testing Aged binder Since fatigue is a long term performance problem, include: Short term aging Long term aging Determine DSR parameters using 8 mm plate and intermediate test temperature Superpave Performance Graded Binder Tests 33

34 Pressure Aging Vessel (Long Term Aging) Simulates aging of an asphalt binder for 7 to 10 years 50 gram sample is aged for 20 hours Pressure of 2,070 kpa (300 psi) At 90, 100 or 110 C Superpave Performance Graded Binder Tests 34

35 Pressure Aging Vessel Superpave Performance Graded Binder Tests 35

36 Pressure Aging Vessel Courtesy of FHWA Superpave Performance Graded Binder Tests 36

37 Fatigue Cracking G* (sin δ) on RTFO and PAV aged binder The parameter addresses the later part of the fatigue life Value must be < 5000 kpa Superpave Performance Graded Binder Tests 37

38 Fatigue Cracking Question: Why a maximum G* sin δ to address fatigue? Answer: We want a soft elastic binder (to sustain many loads without cracking) How: By decreasing G* or decreasing δ Superpave Performance Graded Binder Tests 38

39 Thermal Cracking RV DSR BBR Superpave Performance Graded Binder Tests 39

40 Bending Beam Rheometer Computer Deflection Transducer Air Bearing Load Cell Fluid Bath Superpave Performance Graded Binder Tests 40

41 Bending Beam Rheometer Sample Superpave Performance Graded Binder Tests 41

42 Bending Beam Rheometer Equipment Fluid Bath Loading Ram Cooling System Superpave Performance Graded Binder Tests 42

43 Superpave Performance Graded Binder Tests 43

44 Bending Beam Rheometer S(t) = P L 3 4 b h 3 δ (t) Where: S(t) = creep stiffness (M Pa) at time, t P = applied constant load, N L = distance between beam supports (102 mm) b = beam width, 12.5 mm h = beam thickness, 6.25 mm d(t) = deflection (mm) at time, t Superpave Performance Graded Binder Tests 44

45 Bending Beam Rheometer Evaluates low temperature stiffness properties Creep stiffness Slope of response (called m-value) Log Creep Stiffness, S(t) Log Loading Time, t (sec) Superpave Performance Graded Binder Tests 45

46 Is Stiffness Enough? Need to assess strength at low temperatures Thermal cracking occurs when thermal stress exceeds pavement strength Direct tension test Combined with BBR results to calculate critical cracking temperature (t crit ) States choice to use AASHTO M320 or MP-1a DTT is no longer an option in AASHTO M320 Superpave Performance Graded Binder Tests 46

47 Direct Tension Test Courtesy of Instron Superpave Performance Graded Binder Tests 47

48 Direct Tension Test Courtesy of FHWA Superpave Performance Graded Binder Tests 48

49 Superpave Performance Graded Binder Tests 49

50 Top View ball joint pins specimen inserts Side View Superpave Performance Graded Binder Tests 50

51 L L e Load Failure L L+ Δ L Failure load failure stress (σ f ) = Original cross-section area Superpave Performance Graded Binder Tests 51

52 DTT Data stress σ f Constant Strain Rate ε f strain Superpave Performance Graded Binder Tests 52

53 Different Binders or Temps stress brittle brittle-ductile ductile Different types of behavior strain Superpave Performance Graded Binder Tests 53

54 Failure Strain, % = 1 brittle brittle-ductile ductile Temperature Superpave Performance Graded Binder Tests 54

55 stress modified unmodified strain Superpave Performance Graded Binder Tests 55

56 What Do You Need to Calculate T crit? BBR Data for at least 2 Temperatures 8, 15, 30, 60, 120, and 240 seconds Stiffness, MPa DTT Data for at least 1 Temperature Failure Stress, MPa TSAR software Superpave Performance Graded Binder Tests 56

57 Superpave Performance Graded Binder Tests 57

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59 Tcrit = the temperature at which the thermal stress in the material (BBR) exceeds its strength (DTT) Superpave Performance Graded Binder Tests 59

60 Summary Construction Rutting Fatigue Cracking Low Temp Cracking [DTT] [RV] [DSR] [BBR] No aging RTFO Short Term Aging PAV Long Term Aging Superpave Performance Graded Binder Tests 60

61 Questions does it all make sense? Superpave Performance Graded Binder Tests 61