Asphalt 101: An Introduction to Hot Mix Asphalt Materials. -Part I- Asphalt and Modified Asphalts. Scott Shuler CSU

Transcription

1 Asphalt 101: An Introduction to Hot Mix Asphalt Materials -Part I- Asphalt and Modified Asphalts Scott Shuler CSU 1

2 Glue: Scott Shuler Sticky Glue: Marshall Shackelford 2

3 Why Study Asphalt? 2,200,000 of all the ROADS IN THE U. S. A. (miles) 1,300, , ,000 Concrete Earth Gravel Asphalt 5% 95% 3

4 Why Study Asphalt? Highway Expenditures in 2008 $140 Billion Hot Mix Asphalt Placed Annually 500 Million Tons $10.5 Billion Employment 300,000 directly 600,000 additionally Asphalt is Largely Empirical Old Timers Retiring 4

5 What Are Asphalt Pavements? Rocks Glued Together With Asphalt Rocks Volume About 86% Asphalt About 10% Air 4% 5

6 Let s s Consider the Glue Among the Oldest Engineering Materials Waterproofing of Ships Sumeria-6000 BC Waterproofing of Baths and Tanks Earth Butter Mohenjo-Daro Indus Valley-3000 BC Mummies Egypt-2600 BC Bible References Noah s Arc Waterproofed with Pitch Genesis 6:14.20 Moses Basket Coated with Bitumen and Pitch Exodus 2:3.24 Roman Buildings Waterproofed and Cemented Romans called the source Lacus Asphaltites 6

7 So It Will Work! 7

8 Reed Boat, aka Gufa 8

9 Bitumen Asphalts Tars Natural Petroleum Coal 9

10 Asphalts Natural Petroleum Trinidad La Brea Lake Cements Liquids KY TX AB Rock Asphaltites Emulsions Cutbacks UT-Gilsonite 10

11 Crude Oil Variations Venezuelan Gasoline 3% Kerosene 6% Gas Oil 33% Residuum 58% Nigerian Light Gasoline 33% Kerosene 20% Gas Oil 46% Residuum 1% 11

12 Refining Methods Distillation Atmospheric Vacuum Solvent Deasphalting Propane and Butane Extraction of Lube Oils Result is Very Hard Precipitate AC Solvent Extraction (ROSE) Separates AC into Asphaltenes/Resins/Oils Result is Blended to Produce Spec AC 12

13 Petroleum Asphalts Oil Well Crude Storage F F Gasoline Kerosene F Gas Oil Atmos Still F Condenser F Vacuum Still Air Roofing Asphalts Asphalt Cements H 2 O Gas/ Kero Emulsions Cutbacks 13

14 Asphalt Types Asphalt Cement Liquid Asphalts Emulsified Asphalts Cutback Asphalts 14

15 Behavior of Asphalt Cements Asphalt is Viscoelastic Viscous (Flows) at High Temperatures Elastic at Low Temperatures Silly Putty is Viscoelastic Pull it Slowly- It stretches same as high temperature Pull it Rapidly It breaks same as low temperature 15

16 Asphalt Performance depends on Environment and Traffic 16

17 Weak Behavior Hot Behavior Cold Behavior 17

18 Temperature Effects 1 Hour 100 F 10 Hours 30 F 18

19 Material Effects 1 Hour 30 F Hard Asphalt Softer Asphalt 19

20 SUPERPAVE Achieving Performance To The Rescue! 20

21 SPECIFYING PERFORMANCE Based on Climate PG Performance Grade Average 7-day max pavement temperature, C Min pavement temperature, C 21

22 Tests in PG Specifications Dynamic Shear Rheometer Bending Beam Rheometer Rotational Viscometer 22

23 Permanent Deformation ( ) Courtesy of FHWA Caused by Warm Weather, Traffic and Wrong Mixture 23

24 High Temperature or, Slow Loading Behavior, aka Rutting High Pavement Temperature Desert climates Summer temperatures Sustained loads Slow moving trucks Intersections 100 F 1 Hour 24

25 Thermal Cracking Courtesy of FHWA Caused by Low Temperatures, Rapid Loads, Hard Binder 25

26 Low Temperature, or Fast Loading Behavior-aka Cracking Low Temperature Cold climates Winter Rapid Loads Fast moving trucks σ Cracking Failure ε 26

27 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 27

28 Asphalt Plant and Construction Aging Rolling Thin Film Oven (RTFO) Fan Rotating Bottle Carriage Blowing Air 28

29 Pressure Aging Vessel 50 grams of Asphalt in Each Pan Pressure Aging Vessel 29

30 Pressure Aging Vessel Courtesy of FHWA 30

31 Rutting, Hardening and Fatigue DSR BBR RV 31

32 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 32

33 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 33

34 Complex Modulus, G* δ Viscous, G Elastic, G Complex Modulus is the vector sum of Elastic and Viscous Components 34

35 Controlling Rutting Addressed by: G*/sin δ on Unaged binder > 1.00 kpa G*/sin δ on Lab Aged binder > 2.20 kpa Heavy Trucks > Early part of pavement life 35

36 Caused by repeated traffic loads in wheel paths Fatigue Cracking 36

37 Fatigue Cracking Addressed by intermediate temperature stiffness G*sin δ on RTFO & PAV aged binder < 5000 kpa > Later part of pavement service life 37

38 Thermal Cracking RV DSR BBR 38

39 Bending Beam Rheometer Computer Deflection Transducer Load Cell Fluid Bath 39

40 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 40

41 Bending Beam Rheometer Creep Stiffness Stiffness v. Time Slope Log Creep Stiffness, S(t) m Log Loading Time, t (sec) 41

42 Thermal Cracking Question: How Much Should the Asphalt Be Able to Stretch before Breaking? Answer: at least 1% How: Find the Temperature Where the Asphalt Can Stretch 1% or More 42

43 Direct Tension Test Load Stress = σ = P / A Δ L σ f Δ L e Strain ε f 43

44 But Will it Flow for Mixing? Construction Rotational Viscometer RV Dynamic Shear Rheometer Bending Beam Rheometer 44

45 Rotational Viscometer (Brookfield) Torque Motor Inner Cylinder Thermosel Environmental Chamber Digital Temperature Controller 45

46 Spec Requirements Make Sure It s Not Too Thick Keep Viscosity Below 3 Pa-sec at 275F (135C) 46

47 Questions... 47