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Selecting the Correct PG Asphalt for Your Airport Project 29 th Annual FAA Airports Conference Hershey, PA March 2, 2006 Ronald Corun CITGO Asphalt Technical.

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Presentation on theme: "Selecting the Correct PG Asphalt for Your Airport Project 29 th Annual FAA Airports Conference Hershey, PA March 2, 2006 Ronald Corun CITGO Asphalt Technical."— Presentation transcript:

1 Selecting the Correct PG Asphalt for Your Airport Project 29 th Annual FAA Airports Conference Hershey, PA March 2, 2006 Ronald Corun CITGO Asphalt Technical Support Manager A Driving Force In Asphalt CITGO Petroleum Corporation

2 What is SUPERPAVE? u New Asphalt Binder specification u New Mix Design procedure using a new laboratory compaction device

3 We Have Three Asphalt Binders u Q. How do we determine which asphalt binder is best for our project? u A. The asphalt binder that gives the best performance ABC

4 Performance ? u Q. What areas of poor performance do we want to avoid ? u Or, in other words, how do our asphalt pavements fail ?

5 How do asphalt pavements fail ?

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9 How Did We Measure Asphalt Properties Before the PG Grading System? u Penetration Grading u Viscosity Grading

10 100 g penetration 0 sec 5 sec Penetration Viscosity vacuum 25° C 60° C

11 Problem with one temperature grading

12 u According to the Penetration system: u According to the Viscosity System:

13 Asphalt binders u Q. Are the properties of asphalt binders constant over a pavements performance life? u A. NO! An asphalt binders response to loading is a function of three factors... u Age u Temperature u Rate of Loading

14 Asphalt binders response to loading is a function of... 1. age

15 Aging u Asphalt binders undergo aging through the loss of volatiles (a.k.a. loss of light ends) and oxidation. u From the standpoint of determining an asphalt binder's performance there are three key ages we need to address.

16 Key Aging u New material - no aging u During construction u Aging in the plant u Aging during placement u Late in the pavement's life u 7 - 10 years of service

17 Aging - How ? u Early: To simulate the aging that occurs due to construction and initial service, we are going to employ the Rolling Thin- Film Oven (RTFO). This is a standard AASHTO test method, T 240. u Spec.: 85 minutes, 163°C, 400 ml of air per minute, 15 rpm

18 163°C controls fan bottle carriage air jet Rolling Thin Film Oven

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20 Rolling Thin Film Oven Sample Bottles Clean Bottle Before Loading After LoadingCoated Bottle After Testing

21 Aging - How ? u Long term: To simulate the aging that occurs due to oxidation over a pavement's life, we are going to subject the RTFO residue to time, temperature, and pressure. For this we are going to develop a pressure aging vessel, (PAV).

22 Aging - How ? u Long term, Spec.: AASHTO PP1. u According to PP1, our RTFO residue is subjected to: u Temperature: 90 to 110°C u Time: 20 hours u Pressure: 2.1 kPa

23 asphalt sample pan sample rack pressure vessel airpressuretemperatureprobe Pressure Aging Vessel

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25 Asphalt binders response to loading is a function of... 1. age 2. temperature

26 Pavement Temperature, C - 2020 60 135

27 Temperatures u Q. What temperatures do we need to address ? u 1. Rutting occurs at... u 2. Fatigue Cracking occurs at... u 3. Low Temperature Cracking occurs at...

28 Temperatures u 1. Rutting occurs at high pavement temperatures, T (high) u 2. Fatigue Cracking occurs at intermediate pavement temperatures, T (inter), and u 3. Low Temperature Cracking occurs at low pavement temperatures, T (low).

29 Performance Grade Increments

30 Superpave Asphalt Binder Specification u Grading System Based on Climate PG 64-22 PerformanceGrade Average 7-day max pavement design temp Min pavement design temp

31 FatigueCracking Rutting PAV - aging RTFO - aging No aging Pavement Age Construction [RV] [DSR] Low Temp Cracking [BBR] [DTT]

32 Dynamic Shear Rheometer, DSR u Apply a oscillating shear stress Measure strain Measure strain u A materials modulus is u Modulus = Stress / Strain u A measure of material stiffness

33 Dynamic Shear Rheometer, DSR

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40 DSR provides G * and DSR provides G * and u G *, Complex Shear Modulus u, Phase Angle u G * / sin u G * / sin u Correlates to rutting resistance. u G * sin u G * sin u Correlates to fatigue resistance.

41 Rutting Specification - Minimum Stiffness @ T (high) u G * / sin > 1.00 kPa on unaged binder u G * / sin > 2.20 kPa on RTFO aged binder

42 FatigueCracking Rutting PAV - aging RTFO - aging No aging Pavement Age Construction [RV] [DSR] Low Temp Cracking [BBR] [DTT]

43 Fatigue Cracking Specification - Maximum Stiffness @ T (inter) u G * sin < 5000 kPa on PAV aged binder

44 FatigueCracking Rutting PAV - aging RTFO - aging No aging Pavement Age Construction [RV] [DSR] Low Temp Cracking [BBR] [DTT]

45 Superpave Binder Specification Low Temperature Characterization u The Bending Beam Rheometer (BBR) determines the Creep Stiffness (S) of an asphalt binder at low temperatures. u If a binder is too stiff at service temperatures, you can expect low temperature cracking.

46 Bending Beam Rheometer, BBR Fluid Bath Deflection Transducer Load Cell Asphalt Beam Air Bearing Loading Frame Supports Control and Data Acquisition Thermometer

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48 Bending Beam Rheometer, BBR acetate strips rubber O-rings aluminum mold binder specimen in mold 125 mm 6.35 mm 12.7 mm

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52 Bending Beam Rheometer, BBR 980 mN (100 g) Load Asphalt Beam Deflected Position Asphalt Beam Original Position

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54 Bending Beam Rheometer, BBR Time Test Load Deflection Time

55 Bending Beam Rheometer, BBR 60 sec Time Deflection (t) simulates stiffness after 2 hours at 10 °C lower temp

56 BBR Data - Relaxation Log Creep Stiffness, S Log Loading Time slope = m-value 60 sec 81530 120 240 PG Spec

57 Low Temperature Cracking Specification u Maximum Creep Stiffness Value (S) u S < 300 MPa u Minimum m-value u m > 0.300

58 Other PG Binder Tests... u Q. What about Construct-ability ? u A. A better word might be Pump-ability. A concern raised during SHRP was the need to address modified systems. Heavily modified systems can literally burn-out pumps. To address this, we will use ASTM D 4404, "Brookfield Rotational Viscometer."

59 FatigueCracking Rutting PAV - aging RTFO - aging No aging Pavement Age Construction [RV] [DSR] Low Temp Cracking [BBR] [DTT]

60 Rotational Viscometer sample chamber spindle asphalt sample applied torque from motor

61 Rotational Viscometer digital readout temperature controller thermo - container (Thermosel TM ) spindle extension Brookfield viscometer control keys

62 Rotational Viscometer

63 Rotational Viscometer Specification u Viscosity @ 135ºC < 3.0 Pa-s u Run viscosity at both 135ºC and 165ºC to determine laboratory mixing and compaction temperatures

64 .1.2.3.5 1 10 5 100110120130140150160170180190200 Temperature, C Viscosity, Pa s Compaction Range Mixing Range Lab Mixing & Compaction Temperatures

65 Asphalt binders response to loading is a function of... 1. age 2. temperature 3. rate of loading

66 60 C 25 C 1 hour Time vs. Temperature 10 hours

67 Effect of Traffic Speed on Binder Stiffness PG Spec 2.2 kPa

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70 FHWA ALF Binder Study Rut Depth, mm 30 mm Asphalt Binder Grade 24 mm 4 mm Rut Depth @ 5000 passes of ALF 11 mph @ 58ºC 11 mph @ 58ºC

71 Effect of Loading Rate on Binder Selection u Example u for 55 mph highway PG 64-22 u for 30 mph highway PG 70-22 u for intersections PG 76-22 Standard Grade Slow - Bump one grade one grade Stopped - Bump one grade

72 SUPERPAVE Asphalt Binder Specification u Selection is based on u Climate u Traffic speed u Amount of traffic - measured in ESALs u PG grade u Asphalt content of mix - durability

73 PG 70 - 22 = 70 - - 22 = 92 Binder may be modified!! PG 76 - 22 = 76 - - 22 = 98 Binder will be modified !! Rule of 92 Is the PG Binder Modified ? (Depends on Asphalt Source!)

74 Asphalt Modifiers u Change effects of temperature on physical properties u Reduce effects of aging/oxidation u Improve adhesion to aggregates

75 Viscosity Temperature Hard asphalt Soft asphalt Comp MixService Fluid Semi-solid Modification Concept Ideal Asphalt

76 Modifiers that affect consistency: u Natural Asphalts (TLA) u Chemicals u Oxidants u Fibers u Polymers Asphalt Modifiers

77 Polymers u From Greek: many parts u High molecular weight molecules formed from combining simpler molecules/chemical compounds u Styrene- Butadiene-Styrene (SBS) is most widely used polymer in asphalt

78 S SS S S B B B POLY-BUTADIENE POLY-STYRENE Rubber band Disposable fork What is SBS?

79 LINEAR SBS S S B RADIAL SBS S S B S B What is SBS?

80 u Styrene-Butadiene- Styrene u Styrene provides stiffness at high temperatures u Butadiene gives flexibility at low temperatures u Complete dispersion of SBS in asphalt provides best performance

81 How is PMA Produced? u Start with PG 64-22 u Dissolve and Cross-link SBS Molecules u Reaction Time u Constant Agitation u Constant Heat u Test Asphalt Properties u Performance Properties u Homogenous Material u Consistency

82 SBS in Asphalt - Beginning

83 SBS Intermediate Curing

84 Finished SBS Modified Asphalt

85 Superpave Plus Binder Specifications u Used to ensure polymer-modification u Example: PG 76-22 Plus Maximum phase angle of 75 degrees u Test methods u DSR Phase Angle (Engineering value) u Amount of Stretch and/or Recovery (Empirical)

86 Elastic Recovery Neat doesnt recover Modified recovers 1 2 34

87 PG Binder Selection for Airports u How do we get from ESALs to Airplanes? u Airfield Asphalt Pavement Technology Program (AAPTP) u Research funded by AIR-21 u Managed by Auburn University u Primarily will research adapting Superpave to airfields u Until research is complete – common sense guidelines developed by FAA and DOD

88 FAA and DoD General Guidelines for Binder Grade Selection on Airfields Consult with local DOT Consult with local DOT u Determine grades that are typically being used and are available for the particular area u Determine the Standard Grade u Typically used for highways with less than 10 million ESALs u Sufficient on most GA airports u Consider Bumping for top 5 inches if concerned u Past performance? u High tire pressures? u Standing or slow traffic (stacking on TWs)? u Channelized traffic (alleyways)?

89 u For Aircraft < 12,500 lbs PG 64-22 u For Aircraft < 100,000 lbs PG 70-22 or PG 76-22 u For Aircraft > 100,000 lbs PG 76-22 or PG 82-22 u Need to Consider Traffic Flow Grade Bumping Example - Airfields

90 The higher the Grade, the stiffer the binder. The more rut resistance. PG 82 PG 76 PG 70 PG 64 PG 58 Rule # 1

91 The lower the number, the more resistant to thermal cracking. PG- 22 - 28 -34 Rule # 2

92 Rule # 3 PG 82 O 22 O PG 76 O 22 O PG 70 O 22 O PG 64 O 28 O PG 64 O 22 O PG 58 O 28 O 104 O 98 O 92 O 86 O The greater the difference the higher the cost. Mix Cost + 3 - 5% Mix Cost + 15-20%

93 CONCLUSIONS u Training needed for everyone if SUPERPAVE is to be used successfully u PG Grade System provides the right asphalt for varying climate and traffic conditions u SUPERPAVE places more tools in the Pavement Designers Tool Box u Designers can solve pavement problems they were unable to in the past using SUPERPAVE SUPERPAVE

94 Questions?

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