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

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

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

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

How do asphalt pavements fail ?

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

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

Problem with one temperature grading

Problem with one temperature grading According to the Penetration system: According to the Viscosity System:

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

Asphalt binder’s response to loading is a function of. . . 1. age

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

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

Aging - How ? 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. Spec.: 85 minutes, 163°C, 400 ml of air per minute, 15 rpm

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

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

Aging - How ? 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).

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

Pressure Aging Vessel asphalt sample pan sample rack pressure vessel air pressure temperature probe

Asphalt binder’s response to loading is a function of. . . 1. age 2. temperature

Pavement Temperature, C - 20 20 60 135 Pavement Temperature, C

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

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

Performance Grade Increments

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

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

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

Dynamic Shear Rheometer, DSR

Dynamic Shear Rheometer, DSR

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

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

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

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

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

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

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

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

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

Bending Beam Rheometer, BBR Time Test Load Deflection Time

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

BBR Data - Relaxation slope = m-value 60 sec Log Creep Stiffness, S PG Spec slope = m-value Log Loading Time 60 sec 8 15 30 120 240

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

Other PG Binder Tests . . . Q. What about Construct-ability ? 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."

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

Rotational Viscometer applied torque from motor spindle asphalt sample sample chamber

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

Rotational Viscometer

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

Lab Mixing & Compaction Temperatures Viscosity, Pa s 10 5 1 .5 .3 Compaction Range .2 Mixing Range .1 100 110 120 130 140 150 160 170 180 190 200 Temperature, C

Asphalt binder’s response to loading is a function of. . . 1. age 2. temperature 3. rate of loading

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

Effect of Traffic Speed on Binder Stiffness PG Spec 2.2 kPa

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

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

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

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

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

Modification Concept Viscosity Temperature “Hard” asphalt “Ideal” Asphalt Semi-solid Viscosity “Soft” asphalt Fluid Service Comp Mix Temperature

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

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

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

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

What is SBS? Styrene-Butadiene-Styrene Styrene provides stiffness at high temperatures Butadiene gives flexibility at low temperatures Complete dispersion of SBS in asphalt provides best performance

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

SBS in Asphalt - Beginning

SBS Intermediate Curing

Finished SBS Modified Asphalt

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

Elastic Recovery 2 1 Neat doesn’t recover Modified recovers 3 4

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

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

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

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

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

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

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

Questions?