Performance Graded (PG) Asphalts

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Randell Goodman
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1 Performance Graded (PG) Asphalts A Driving Force In Asphalt SUPERPAVE Update for NJDOT/NEAUPG Mechanistic Pavement Design Seminar Princeton, NJ - Feb. 25, 2003

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

3 Q. 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. A B C

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

5 How do asphalt pavements fail? SP

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

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

11 Problem with one temperature grading HARD PEN VISC A SOFT 25 C 60 C A B C B C

12 Problem with one temperature grading According to the Penetration system: According to the Viscosity System: B A = = C C HARD SOFT PEN 25 C VISC 60 C A B C A B C

13 Need to Correct this Problem Develop Preformance Related tests and specification Asphalt is a visco-elastic material Protocols need to be Temperature based

14 ? 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).

15 ? 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.

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

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

18 Pavement Temperature, C

19 Weather Database Performance Grade Increments Average 7-day Maximum Pavement Temperature Average 1-day Minimum Pavement Temperature

20 Superpave Asphalt Binder Specification Grading System Based on Climate PG Performance Grade Average 7-day7 max pavement design temp Min pavement design temp

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

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

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

24 Rutting Specification - Minimum T (high) G * / sin δ > 1.00 kpa on unaged binder G * / sin δ > 2.20 kpa on RTFO aged binder

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

26 Fatigue Cracking Specification - Maximum T (inter) G * sin δ < 5000 kpa on PAV aged binder

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

28 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.

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

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

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

32 Bending Beam Rheometer, BBR Test Load Time Deflection Time

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

34 BBR Data - Relaxation Log Creep Stiffness, S slope = m-value PG Spec Log Loading Time sec

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

36 Direct Tension Test, DTT L L e Load L Failure failure strain (ε f ) = change in length ( L) effective gauge length (L e )

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

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

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

40 Rotational Viscometer

Rotational Viscometer Specification Viscosity @ 135ºC < 3.

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

42 Lab Mixing & Compaction Temperatures for Unmodified Asphalt 10 Viscosity, 5 Pa s Compaction Range Mixing Range Temperature, C

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

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

45 FHWA ALF PG Binder Study

47 FHWA ALF Binder Study Rut 5000 passes of ALF 11 58ºC mm 24 mm 20 Rut Depth, mm mm AC-10 AC-20 PMA 0 PG PG PG Asphalt Binder Grade

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

49 67 kn 15,000 lb 0.48 ESAL 27 kn 6,000 lb 0.01 ESAL + = 0.49 ESALs 151 kn 34,000 lb kn 34,000 lb 54 kn 12,000 lb = ESALs

50 Effect of Traffic Amount on Binder Selection Traffic Loads on the pavement are measured in Equivalent Single Axle Loads (ESAL) 20 year ESAL measurements are required in the SUPERPAVE system to correctly determine asphalt binder PG grade

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

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

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

54 Rule # 2 PG The lower the number, the more resistant to thermal cracking.

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

56 Questions?

Asphalt 101 Materials: HMA Part 1. Rocky Mountain Asphalt Conference and Equipment Show. February 24, 2011

Asphalt 101 Materials: HMA Part 1 Rocky Mountain Asphalt Conference and Equipment Show February 24, 2011 1 SUPERPAVE 2 SUPERPAVE 2 SPECIFYING PERFORMANCE Based on Climate PG 58-28 Performance Grade Min