- New Superpave Performance Graded Specification. Asphalt Cements

Transcription

1 - New Superpave Performance Graded Specification Asphalt Cements 1

2 PG Specifications Fundamental properties related to pavement performance Environmental factors In-service & construction temperatures Short and long term aging 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) 3

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

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

6 Permanent Deformation Courtesy of FHWA Function of warm weather and traffic 6

7 Low Temperature Behavior Low Temperature Cold climates Winter Rapid Loads Fast moving trucks Elastic Solid Hooke s Law s = t E 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 8

9 Thermal Cracking Courtesy of FHWA 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) 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 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) 12

13 Tests Used in PG Specifications Construction RV DSR BBR 13

14 Concentric Cylinder Rheometers Concentric Cylinder t Rq = M i 2 p R i 2 L g = W R R o - R i 14

15 Rotational Viscometer (Brookfield) Torque Motor Inner Cylinder Thermosel Environmental Chamber Digital Temperature Controller 15

16 Original Properties, Rutting, and Fatigue DSR RV BBR 16

17 Dynamic Shear Rheometer (DSR) Parallel Plate Shear flow varies with gap height and radius Non-homogeneous flow t R = 2 M p R 3 g R = R Q h 17

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

19 Elastic Viscous B A A Strain Time C Strain in-phase d = 0 o Strain out-of-phase d = 90 o 19

20 Complex Modulus, G* Viscous Modulus, G d Storage Modulus, G Complex Modulus is the vector sum of the storage and viscous modulus 20

21 Computer Control and Data Acquisition DSR Equipment DSR Equipment 21

22 Motor Parallel Plates with Sample Area for Liquid Bath 22

23 25 mm Plate with Sample 23

24 Rutting RV BBR DSR 24

25 Permanent Deformation Addressed by: G*/sin d on unaged binder > 1.00 kpa G*/sin d on RTFO aged binder > 2.20 kpa For the early part of the service life 25

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

27 Inside of RTFO Fan Rotating Bottle Carriage Air Line 27

28 Bottles Before and After Testing Opening in Bottle 28

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

30 Permanent Deformation Question: Why a minimum G*/sin d to address rutting Answer: We want a stiff, elastic binder to contribute to mix rutting resistance How: By increasing G* or decreasing d 30

31 Fatigue RV BBR DSR 31

32 Fatigue Cracking Function of repeated traffic loads over time (in wheel paths) 32

33 Testing Aged binder Since long term performance problem, include: Short term aging Long term aging Determine DSR parameters using 8 mm plate and intermediate test temperature 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 34

35 Pressure Aging Vessel Rack of individual pans (50g of asphalt / pan) Bottom of pressure aging vessel Vessel Lid Components 35

36 Pressure Aging Vessel Courtesy of FHWA 36

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

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

39 Thermal Cracking RV DSR BBR 39

40 Bending Beam Rheometer Computer Deflection Transducer Air Bearing Load Cell Fluid Bath 40

41 Bending Beam Rheometer Sample 41

42 Bending Beam Rheometer Equipment Fluid Bath Loading Ram Cooling System 42

43 Bending Beam Rheometer S(t) = P L 3 4 b h 3 d (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 43

44 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) 44

45 Is Stiffness Enough? No. Need to assess strain needed to break specimen. Thermal cracking occurs when strain is too great Direct tension test Currently (1998) in specification New equipment is now available 45

46 Direct Tension Test Load Stress = s = P / A D L s f D L e Strain e f 46

47 Direct Tension Test FHWA Courtesy of FHWA 47

48 Direct Tension Test Courtesy of FHWA 48

49 Summary Construction Rutting Fatigue Cracking Low Temp Cracking [DTT] [RV] [DSR] [BBR] No aging RTFO Short Term Aging PAV Long Term Aging 49

50 Superpave Binder Purchase Specification

51 Superpave Asphalt Binder Specification The grading system is based on Climate PG Performance Grade Min pavement temperature Average 7-day max pavement temperature

52 Performance Grades CEC Avg 7-day Max, o C 1-day Min, o C > 230 o C < 3 Pa. 135 o C PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG (Flash Point) FP (Rotational Viscosity) ORIGINAL RV > 1.00 kpa (Dynamic Shear Rheometer) DSR G*/sin d (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % > 2.20 kpa 20 Hours, 2.07 MPa < 5000 kpa S < 300 MPa m > Report Value > 1.00 % (Dynamic Shear Rheometer) (PRESSURE AGING VESSEL) (110) 100 (110) 110 (110) (Dynamic Shear Rheometer) (Bending Beam Rheometer) BBR Physical Hardening (Direct Tension) DSR G*/sin d PAV DSR G* sin d ( Bending Beam Rheometer) BBR S Stiffness & m - value DT

53 How the PG Spec Works CEC Spec Requirement Remains Constant Avg 7-day Max, o C 1-day Min, o C > 230 o C < 3 Pa. 135 o C PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG (Flash Point) FP (Rotational Viscosity) ORIGINAL RV > 1.00 kpa (Dynamic Shear Rheometer) DSR G*/sin d (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % > 2.20 kpa 20 Hours, 2.07 MPa < 5000 kpa (Dynamic Shear Rheometer) DSR G*/sin d (PRESSURE AGING VESSEL) PAV (110) 100 (110) 110 (110) Test Temperature Changes (Dynamic Shear Rheometer) DSR G* sin d S < 300 MPa m > ( Bending Beam Rheometer) BBR S Stiffness & m - value Report Value > 1.00 % (Bending Beam Rheometer) BBR Physical Hardening (Direct Tension) DT

54 Permanent Deformation CEC Avg 7-day Max, o C 1-day Min, o C > 230 o C < 3 Pa. 135 o C PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG (Flash Point) FP (Rotational Viscosity) ORIGINAL RV > 1.00 kpa > 2.20 kpa Unaged RTFO Aged 20 Hours, 2.07 MPa < 5000 kpa S < 300 MPa m > Report Value > 1.00 % (Dynamic Shear Rheometer) (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % (Dynamic Shear Rheometer) (PRESSURE AGING VESSEL) (110) 100 (110) 110 (110) (Dynamic Shear Rheometer) (Bending Beam Rheometer) BBR Physical Hardening (Direct Tension) DSR G*/sin d DSR G*/sin d PAV DSR G* sin d ( Bending Beam Rheometer) BBR S Stiffness & m - value DT

55 Permanent Deformation Addressed by high temp stiffness G*/sin d on unaged binder > 1.00 kpa G*/sin d on RTFO aged binder > 2.20 kpa Heavy Trucks > Early part of pavement service life

56 Fatigue Cracking CEC Avg 7-day Max, o C 1-day Min, o C > 230 o C < 3 Pa. 135 o C PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG (Flash Point) FP (Rotational Viscosity) ORIGINAL RV > 1.00 kpa (Dynamic Shear Rheometer) DSR G*/sin d (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % > 2.20 kpa 20 Hours, 2.07 MPa (Dynamic Shear Rheometer) DSR G*/sin d (PRESSURE AGING VESSEL) PAV (110) 100 (110) 110 (110) < 5000 kpa PAV Aged S < 300 MPa m > Report Value > 1.00 % (Dynamic Shear Rheometer) (Bending Beam Rheometer) BBR Physical Hardening (Direct Tension) DSR G* sin d ( Bending Beam Rheometer) BBR S Stiffness & m - value DT

57 Fatigue Cracking Addressed by intermediate temperature stiffness G*sin d on RTFO & PAV aged binder < 5000 kpa > Later part of pavement service life

58 Low Temperature Cracking CEC Avg 7-day Max, o C 1-day Min, o C > 230 o C < 3 Pa. 135 o C PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG (Flash Point) FP (Rotational Viscosity) ORIGINAL RV > 1.00 kpa (Dynamic Shear Rheometer) DSR G*/sin d (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % > 2.20 kpa 20 Hours, 2.07 MPa (Dynamic Shear Rheometer) DSR G*/sin d (PRESSURE AGING VESSEL) PAV (110) 100 (110) 110 (110) < 5000 kpa S < 300 MPa m > PAV Aged Report Value > 1.00 % (Dynamic Shear Rheometer) (Bending Beam Rheometer) BBR Physical Hardening (Direct Tension) DSR G* sin d ( Bending Beam Rheometer) BBR S Stiffness & m - value DT

59 Low Temperature Cracking CEC Avg 7-day Max, o C 1-day Min, o C > 230 o C < 3 Pa. 135 o C PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG (Flash Point) FP (Rotational Viscosity) ORIGINAL RV > 1.00 kpa (Dynamic Shear Rheometer) DSR G*/sin d (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % > 2.20 kpa 20 Hours, 2.07 MPa (Dynamic Shear Rheometer) DSR G*/sin d (PRESSURE AGING VESSEL) PAV (110) 100 (110) 110 (110) < 5000 kpa S < 300 MPa m > PAV Aged Report Value > 1.00 % (Dynamic Shear Rheometer) (Bending Beam Rheometer) BBR Physical Hardening (Direct Tension) DSR G* sin d ( Bending Beam Rheometer) BBR S Stiffness & m - value DT

60 Miscellaneous Spec Requirements CEC Avg 7-day Max, o C 1-day Min, o C > 230 o C Flash Point < 3 Pa. 135 o C > 1.00 kpa > 2.20 kpa 20 Hours, 2.07 MPa PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG (Flash Point) FP (Rotational Viscosity) (Dynamic Shear Rheometer) RV (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % (Dynamic Shear Rheometer) (PRESSURE AGING VESSEL) ORIGINAL DSR G*/sin d DSR G*/sin d PAV Mass Loss (110) 100 (110) 110 (110) < 5000 kpa S < 300 MPa m > Report Value > 1.00 % (Dynamic Shear Rheometer) (Bending Beam Rheometer) BBR Physical Hardening (Direct Tension) DSR G* sin d ( Bending Beam Rheometer) BBR S Stiffness & m - value DT

61 PG 64-16

62 PG Binder Selection PG > Many agencies have established zones PG PG PG 64-10

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65 Developed from Air Temperatures > 20 years Superpave Weather Database 6500 stations in U.S. and Canada Annual air temperatures hottest seven-day temp (avg and std dev) coldest temp (avg and std dev) Calculated pavement temps used in PG selection

66 Reliability Percent Probability of Not Exceeding Design Temp > using Normal Distribution frequency of observed temps (Total area under curve = 100 %) Reliability is area under curve to the left of T des T avg T des

67 Observed Air Temperatures Topeka, KS 50 % reliability average summer very hot summer 98 % reliability Day Maximum Air Temperatures > this data - standard deviation of 2 C

68 Observed Air Temperatures Topeka, KS 36 very cold winter 40 average winter > standard deviation of 4 C

69 Convert to Pavement Temperature Calculated by Superpave software High Temperature 20 mm below surface of mixture Low Temperature at surface of mixture Pavt Temp = f ( Air Temp, Depth, Latitude )

70 Calculated Pavement Temperatures Topeka, KS pvt > air pvt = air

71 PG Binder Grades Topeka, KS PG (98% minimum reliability) PG (50 % minimum reliability) PG grades - six degree increments

72 Effect of Rounding to Standard Grades PG (50 % minimum reliability) PG -28 provides 90% reliability PG 58 provides 85% reliability

73 Effect of Rounding to Standard Grades needed grade for 50% reliability selected grade for 50% reliability Rounding depends on actual temps! Minimum Pavement Temperatures

74 Effect of Loading Rate on Binder Selection Dilemma specified DSR loading rate is 10 rad/sec what about longer loading times? Use binder with more stiffness at higher temps slow - - increase one high temp grade stationary - - increase two high temp grades no effect on low temp grade 90 kph

75 Effect of Loading Rate on Binder Selection Example for toll road PG for toll booth PG for weigh stations PG kph Slow Stopping

76 Effect of Traffic Amount on Binder Selection 80 kn ESALs x 10 6 ESAL Consider increasing - - one high temp grade 30 x ESAL Recommend increasing - - one high temp grade > Equivalent Single Axle Loads

77 ESAL Comparison 80 kn 18,000 lb. 100 kn 22,000 lb. 44 kn 10,000 lb. 1 ESAL 2.2 ESAL.09 ESAL

78 Little Truck 67 kn 15,000 lb 0.48 ESAL 27 kn + 6,000 lb = 0.01 ESAL 0.49 ESALs BIG TRUCK 151 kn 34,000 lb kn 54 kn + 34,000 lb + 12,000 lb = ESALs

79 How the PG Spec Works CEC Spec Requirement Remains Constant Avg 7-day Max, o C 1-day Min, o C > 230 o C < 3 Pa. 135 o C PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG (Flash Point) FP (Rotational Viscosity) ORIGINAL RV > 1.00 kpa (Dynamic Shear Rheometer) DSR G*/sin d (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % > 2.20 kpa 20 Hours, 2.07 MPa < 5000 kpa (Dynamic Shear Rheometer) DSR G*/sin d (PRESSURE AGING VESSEL) PAV (110) 100 (110) 110 (110) Test Temperature Changes (Dynamic Shear Rheometer) DSR G* sin d S < 300 MPa m > ( Bending Beam Rheometer) BBR S Stiffness & m - value Report Value > 1.00 % (Bending Beam Rheometer) BBR Physical Hardening (Direct Tension) DT

80 Summary of How to Use Determine PG Specification 7-day max pavement temperatures 1-day minimum pavement temperature Use specification tables to select test temperatures Determine asphalt cement properties and compare to specification limits

81 Questions -?

82 Questions -? 82