Asphalt 101 Materials: HMA Part 1. Rocky Mountain Asphalt Conference and Equipment Show. February 18, 2009

Transcription

1 Asphalt 101 Materials: HMA Part 1 Rocky Mountain Asphalt Conference and Equipment Show February 18,

2 SUPERPAVE Achieving Performance 2

3 Weak Behavior Hot Behavior Cold Behavior 3

4 SPECIFYING PERFORMANCE Based on Climate PG Performance Grade Rolling average 7-day max pavement temperature, C Min pavement temperature, C 4

5 To characterize (test) a PG binder individual tests - 6 major pieces of equipment - 3 conditioning steps - ~25 hours total time elapse 5

6 PG Binder Tests vs. Temperature BBR & DTT (Thermal Cracking Resistance) DSR Intermediate Temperature (Fatigue Resistance) DSR High Temperature (Rutting Resistance) Brookfield Viscosity (Workability) Cold Pavement Temperature, C Hot

7 Binder Test Sequence Binder Condition Test For Unaged Binder Flash Rot Vis DSR Safety Handling Rutting RTFO Aged PAV Aged DSR LOH DSR BBR DTT Rutting Environment / Aging Fatigue Damage Thermal Cracking Thermal Cracking

8 Aging Asphalt reacts with oxygen Becomes harder, more brittle More Elastic, Less Viscous Short term During Mixing with Aggregates (280F-330F) Long term In Pavement Air, Water, Sun 8

9 Asphalt Plant and Construction Aging Rolling Thin Film Oven (RTFO) Fan Rotating Bottle Carriage Blowing Air 9

10 Pressure Aging Vessel 50 grams of Asphalt in Each Pan Pressure Aging Vessel 10

11 Pressure Aging Vessel Courtesy of FHWA 11

12 Binder Test Sequence Binder Condition Test For Unaged Binder Flash Rot Vis DSR Safety Handling Rutting RTFO Aged PAV Aged DSR LOH DSR BBR DTT Rutting Environment / Aging Fatigue Damage Thermal Cracking Thermal Cracking

13 Is the binder safe to be heated? Construction RV 13

14 Cleveland Open Cup Flash Point Tester 14

15 Spec Requirement Binder safe to be heated... Cleveland Open Cup (COC) Flash Point must be greater than 235 o C (450 o F). 15

16 Binder Test Sequence Binder Condition Test For Unaged Binder Flash Rot Vis DSR Safety Handling Rutting RTFO Aged PAV Aged DSR LOH DSR BBR DTT Rutting Environment / Aging Fatigue Damage Thermal Cracking Thermal Cracking

17 Will it Flow for Mixing? Construction RV 17

18 Rotational Viscometer (Brookfield) Torque Motor Inner Cylinder Thermosel Environmental Chamber Digital Temperature Controller 18

19 Spec Requirement Make sure binder is not too thick to pump... Keep Viscosity Below 3 Pa-sec at 135 o C (275 o F) 19

20 Binder Test Sequence Binder Condition Test For Unaged Binder Flash Rot Vis DSR Safety Handling Rutting RTFO Aged PAV Aged DSR LOH DSR BBR DTT Rutting, Hardening Environment / Aging Fatigue Damage Thermal Cracking Thermal Cracking

21 Permanent Deformation ( ) Courtesy of FHWA Caused by Warm Weather, Traffic and Wrong Mixture 21

22 High temperature or, slow loading behavior, Rutting High Pavement Temperature Desert climates Summer temperatures 100 F Sustained loads Slow moving trucks Intersections 22

23 Dynamic Shear Rheometer (DSR) Rutting, Hardening, and Fatigue 23

24 Asphalt Glued In- Between B B A C Oscillating Upper Plate Fixed Lower Plate Now, Measure the Force Required to Rotate the Upper Plate And, Measure When Movement Occurs in the Binder A A A Time 1 cycle C 24

25 Elastic Viscous B Stress B A Strain A A Time A A A Strain Occurs With Stress δ = 0 o C C Strain Lags Stress δ = 90 o 25

26 Complex Modulus, G* δ Viscous, G Elastic, G Complex Modulus is the vector sum of Elastic and Viscous Components 26

27 Spec Requirement Mitigate rutting by... G*/sin δ on Unaged binder > 1.00 kpa G*/sin δ on RTFO Aged binder > 2.20 kpa Early part of pavement life 27

28 Binder Test Sequence Binder Condition Test For Unaged Binder Flash Rot Vis DSR Safety Handling Rutting RTFO Aged PAV Aged DSR LOH DSR BBR DTT Rutting Environment / Aging Fatigue Damage Thermal Cracking Thermal Cracking

29 Caused by repeated traffic loads in wheel paths Fatigue Cracking 29

30 Spec Requirement Reduce Fatique Cracking by... G*sin δ on RTFO & PAV aged binder < 5000 kpa Later part of pavement service life 30

31 Binder Test Sequence Binder Condition Test For Unaged Binder Flash Rot Vis DSR Safety Handling Rutting RTFO Aged PAV Aged DSR LOH DSR BBR DTT Rutting Environment / Aging Fatigue Damage Thermal Cracking Thermal Cracking

32 Thermal Cracking Courtesy of FHWA Caused by Low Temperatures, Rapid Loads, Hard Binder 32

33 Low Temperature, or Fast Loading Behavior-aka Cracking Low Temperature Cold climates Winter Rapid Loads Fast moving trucks σ Cracking Failure ε 33

34 Bending Beam Rheometer Thermal Cracking RV BBR 34

35 Bending Beam Rheometer Computer Deflection Transducer Load Cell Fluid Bath 35

36 BBR Measures Stiffness at Low Temperatures using Beam Theory Creep stiffness at t = 60 secs 100 grams Clear Span of Beam, 102 mm S(t) = PL 3 4 bh 3 δ (t) Deflection at t = 60 secs Beam Width, 12.5 mm Beam Thickness, 6.25 mm 36

37 Bending Beam Rheometer Creep Stiffness Stiffness v. Time Slope Log Creep Stiffness, S(t) m Log Loading Time, t (sec) 37

38 Spec Requirement Protect against cracking... BBR m value > BBR S value < 300 MPa 38

39 Binder Test Sequence Binder Condition Test For Unaged Binder Flash Rot Vis DSR Safety Handling Rutting RTFO Aged PAV Aged DSR LOH DSR BBR DTT Rutting Environment / Aging Fatigue Damage Thermal Cracking Thermal Cracking

40 Thermal Cracking Question: How Much Should the Asphalt Be Able to Stretch before Breaking? Answer: at least 1% (in Colorado possibly even more) How: Find the Temperature Where the Asphalt Can Stretch 1% or More 40

41 Direct Tension Test Load Stress = σ = P / A Δ L σ f Δ L e Strain ε f 41

42 Conventional AC Grades vs. SHRP Performance Grades (typical comparisons) AC-5 AC-10 AC-20 AC-40 PG PG PG PG Typical (not absolute) for unmodified asphalts only

43 Benefits of polymer modification Increases temperature spread. Wider field application Stiffer at high temperatures Resists Rutting Less stiff (brittle) at low temperature Resists Cracking More elastic More durable, longer pavement service life Improved adhesion and moisture resistance Resists stripping, raveling and loss of aggregate

44 Binder Performance properties vary with... Concentration of polymer Molecular weight of polymer Chemical composition of polymer Crude source Chemical composition of asphalt Refining process Grade of base asphalt

45 Modified Asphalt Specifications How do you know you re getting a PMAC? Rule of 90 o C temperature spread pg > 86 o C spread (typically non-modified) 58 o C - (-28 o C) = 86 o C pg > 92 o C spread (typically modified) 64 o C - (-28 o C) = 92 o C Modification will expand the temperature spread 45

46 SHRP+ : Physical Properties Insuring that a specific family of modifiers is used for a designated high-performance PG grade Tests which define elastomers: Elastic Recovery Toughness & Tenacity Ductility Maximum Phase Angle MSCR (Multiple Stress Creep Recovery)

47 Questions... 47