Asphalt Specifications and Testing Tri-Party Transportation Conference Brett Lambden March 23-24, 2015

Transcription

1 Asphalt Specifications and Testing Tri-Party Transportation Conference Brett Lambden March 23-24, 2015

2 Overview Asphalt Cement Production Composition Pavement Distresses Previous asphalt specifications PG Specifications PG+ Specifications

3 Asphalt Cement - Production

4 Asphalt Cement - Production Boscan Venezualan Arabian Heavy Nigerian Light API Gravity = Asphalt Heavy crudes are sour ( Sulfur) Light crudes are sweet ( Sulfur)

5 Asphalt Cement - Composition Separating Asphalt Cement Into Broad Chemical Components SARA Analysis

6 Asphalt Cement - Composition

7 Asphalt Cement - Composition

8 Asphalt Cement - Composition Aging Index represents the stiffening of asphalt cement at a given time in service

9 Asphalt Cement Pavement Distresses How do pavements fail and how does it relate to specifications?

10 Asphalt Cement Previous Specifications Culine Cutline

11 Based on rheological testing Rheology: study of flow and deformation Asphalt cement is a viscoelastic material Testing at pavement conditions Behaviour depends on: Temperature Time of loading Aging (properties change with time)

12 Superpave specification attempts to measure properties directly related to pavement field performance. TEST EQUIPMENT PERFORMANCE PROPERTY Rotational Viscometer Dynamic Shear Rheometer Handling Pump Permanent Deformation Fatigue Cracking Flow Rutting Structural Cracking Bending Beam Rheometer Direct Tension Tester Thermal Cracking Low Temp Cracking

13 Performance Grades M (Table 1) CEC Avg 7-day Max, o C 1-day Min, o C > 230 o C < 3 Pa. 135 o C PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG (Flash Point) FP (Rotational Viscosity) ORIGINAL RV > 1.00 kpa (Dynamic Shear Rheometer) DSR G*/sin (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % > 2.20 kpa 20 Hours, 2.07 MPa < 5000 kpa S < 300 MPa m > Report Value > 1.00 % (Dynamic Shear Rheometer) (PRESSURE AGING VESSEL) (110) 100 (110) 110 (110) (Dynamic Shear Rheometer) (Bending Beam Rheometer) BBR Physical Hardening (Direct Tension) DSR G*/sin PAV DSR G* sin ( Bending Beam Rheometer) BBR S Stiffness & m - value DT

14 The grading system is based on climate PG Performance Grade Minimum pavement temperature Average 7-day maximum pavement temperature

15 Pavement Design Temperature Determination LTTPBIND software is most common for this Alternative calculations applicable to Canadian climate (TAC Model) Alberta Transportation did the math and developed a guideline for determining Performance Grade, broken out into zones Bulletin13_ACP.pdf

16 Original Binder Tests Safety Asphalt Cement Flash Point

17 Original Binder Tests Asphalt Binder Viscosity Specification

18 Original, RTFO and PAV Binding Tests Dynamic Shear Rheometer (DSR)

19 The Challenge Explain the rutting and fatigue cracking specifications measured by the Dynamic Shear Rheometer without saying the following: Complex Modulus Phase Angle G* Sinδ Loss Modulus Storage Modulus G G

20 With each traffic cycle, a force is applied to the pavement. Part of this applied force is recovered by the elastic rebound of the pavement surface, while part is dissipated in the form of permanent deformation, heat, cracking and crack propagation. Therefore, in order to minimize rutting, the amount of work dissipated per loading cycle should be minimized. The work dissipated per loading cycle at a constant stress can be expressed as: Where: W c = work dissipated per load cycle σ = stress applied during load cycle G* = complex modulus δ = phase angle In order to minimize the work dissipated per loading cycle, the parameter G*/sinδ should be maximized. Therefore, minimum values for G*/sinδ for the DSR tests conducted on un-aged asphalt binder and RTFO aged asphalt binder are specified.

21 Rutting Parameter G* /sinδ s i n δ sinδ

22 Fatigue Cracking Prevention with Dynamic Shear Rheometer Fatigue cracking can be considered a stress-controlled phenomenon in thick HMA pavements and a strain-controlled phenomenon in thin HMA pavements. Since fatigue cracking is more prevalent in thin pavements, the parameter of most concern for fatigue resistance can be considered a strain-controlled one. The lower the amount of energy dissipated per loading cycle the less likely fatigue cracking is. Therefore, in order to minimize fatigue cracking the amount of work dissipated per loading cycle should be minimized. The work dissipated per loading cycle at a constant strain can be expressed as: = π Where: W c = work dissipated per load cycle ε = strain during load cycle G* = complex modulus δ = phase angle In order to minimize the work dissipated per loading cycle, the parameter G*sinδ should be minimized. Therefore, maximum values for G*sinδ for the DSR tests conducted on PAV aged asphalt binder are specified.

23 Fatigue Cracking Specification

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25 Rolling Thin Film Oven (RTFO) Test

26 Long Term Aging- Pressure Aging Vessel (PAV) Simulates aging binder 7 10 service years 20 hrs at 305 psi PAV temperature depends on grade specified ( C) Original binder RTFO Residue PAV residue

27 Bending Beam Rheometer (BBR)

28 BBR Low Temperature Cracking Specification

29 Time-Temperature Superposition

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31 Direct Tension Test (DDT)

32 Direct Tension Test (DDT) Reproducibility Issues Simple concept but sophisticated measurement device Measures very small strains at low temperatures which requires high degree of precision and accuracy Failure tests in which asphalt binder breaks are an inherent degree of variation in test results In practice test was found to be very irreproducible despite significant research efforts to reduce testing variation Direct Tension Test has not been widely adopted because the inherent variation in test results make it difficult to implement as part of a specification

33 How well does G*/sinδ correlate to rutting in the field?

34 Rutting: Non-Linear Viscoelastic Deformation

35 Multiple Stress Creep Recovery Test (MSCR)

36 MSCR Creep Strain Response

37 Calculating % Recovery In MSCR Test

38 Calculating Jnr in MSCR Test

39 MSCR % Recovery

40 MSCR Specification

41 MSCR Test Identifies Differences in Polymer Network

42 Low Temperature Performance Grade Crude Oil & Modification Requirements for PGAC Binders High Temperature Performance Grade