1. A
ACLAND.BIZ
MAPPING CRACK SUSCEPTIBILITY OF BITUMINOUS MATERIALS WITH BINDER DURABILITY
Daru Widyatmoko & Ric Elliott
(Scott Wilson Pavement Engineering Ltd, UK)
Martin Heslop
(Acland Investment Ltd, UK)

2. Bitumen Hardening Loss of volatiles & oxidative hardening
Heat –production
Heat – delivery/transportation
Heat – paving operation
Age – in service

3. When Bitumen Hardened….
Moderate age - hardening
Increased stiffness
Improved load spreading
Improved rut resistance
Excessive age - hardening
Reduced flexibility
Leading to embrittlement
Reduced capacity to healing

4. Rolling Thin Film Oven Test (RTFOT)
Simulation of short-term ageing
Hardening occurs during the batching process (mixing of aggregate and bitumen at high temperatures)
35 g of bitumen
Test temperature : 163C
Air (O2) flow rate : 4000 ml/min
Test duration : 75 minutes

5. High Pressure Ageing Test (HiPAT)
Simulation of long-term ageing
Modification of Pressure Ageing Vessel procedure
Residue from RTFOT ageing
50 g of bitumen
Test temperature : 85C
Air pressure : 2.1 MPa
Test duration : 65 hours

6. Viscoelasticity of Bitumen
Bitumen is viscoelastic material
Elastic response (fast recovery) at short loading time and/or low temperature -- brittle failure
Viscous response (partial/slow recovery) at long loading time and/or high temperature -- ductile failure

7. Dynamic Shear Rheometer
Controlled Stress Rheometer
Parallel plate: 8 or 25 mm diameter size

8. DSR Oscillatory Loading
time
Position of Oscillating Plate
Oscillating Plate
Applied Stress or Strain A C B
1 cycle
Bitumen C B A
Fixed Plate

9. DSR Oscillatory Loading
t max
Peak Stress
g max
Peak Strain d
time
G * =
Peak Strain
Peak Stress
Complex Modulus
Phase Angle d

10. Stiffer
10/20 Pen
Softer

11. More viscous
More elastic
Straight run
Semi blown
U : Unaged bitumen

12. Viscoelastic response of bitumen
Significant reduction in phase angle (more elastic, less viscous), in particular at low temperature, may lead to increased embrittlement (PIARC 1998)
May contribute to a lower capacity for healing

13. Control
(after RTFOT)
Cracked site
Non-cracked site

14. Straight run Semi blown
Note: The suffix U, R, and H denote binders at unaged, after RTFOT aged and after HiPAT aged conditions.
Straight run
Semi blown

15. Non-cracked
Cracked
More elastic
More viscous

16. VET Temperatures
The Viscous-Elastic Transition (VET) temperature is the temperature at a phase angle value of 45 degrees
The elastic component of the complex shear (stiffness) modulus of a bituminous material equates to the viscous component.
Higher VET was well correlated with the observed surface cracking on several sites in France after 7 years in service (Migliori et al 1999)

17. Viscous-Elastic Transition (VET) Temperature
Non-cracked site
Cracked site 45
VETB8
VETD6

18. VETD6 > VETB8 Viscous-Elastic Transition (VET) Temperature
Non-cracked site
Cracked site 45
VETD6 > VETB8
VETB8
VETD6

19. G* at VET Temperatures
Independent of the viscous or elastic response of a bitumen
Progressive decrease in G*VET with increased age-hardening

20. Straight run Semi blown
Note: The description of the temperature shift U→R→H show the shift from the left to the right axis for the three interconnected data markers for each binder type. The suffix U, R, and H denote binders at unaged, after RTFOT aged and after HiPAT aged conditions.

21. CASE STUDIES
A unique relationship was found by “mapping” G*VET and the presence of cracks observed on some major trunk roads in the United Kingdom

23. Binder Recovered From SMA50
Note: The suffix U, R, and H denote binders at unaged, after RTFOT aged and after HiPAT aged conditions.
Note: The description of the temperature shift U→R→H show the shift from the left to the right axis for the three interconnected data markers for each binder type. The suffix U, R, and H denote binders at unaged, after RTFOT aged and after HiPAT aged conditions.

24. Binder Recovered from HMB15
Straight run
Note: The description of the temperature shift U→R→H only applies for binders B15, C15 and D15 data; showing the shift from the left to the right axis for the three interconnected data markers for each binder type.
Semi blown
Note: The description of the temperature shift U→R→H show the shift from the left to the right axis for the three interconnected data markers for each binder type. The suffix U, R, and H denote binders at unaged, after RTFOT aged and after HiPAT aged conditions.

25. The effect of age-hardening
Progressively change the rheological properties of the penetration grade binders towards stiffer, more elastic, materials.
Binders tested after a laboratory long-term ageing procedure, HiPAT, appeared to be indicative of in situ binder durability for UK conditions.

26. VET Temperatures
As the level of distress increases (e.g. cracked areas), the VET temperature increases but the complex modulus (at the VET temperature) decreases, and vice versa.
As the level of age hardening increases, the VET temperature increases but the complex modulus (at the VET temperature) decreases, and vice versa.

27. However….
Prediction of mixture performance based on binder behaviour is not straightforward,

28. Mixture design, with volumetrics and buildability in mind, are the key elements for satisfactory performance,
and to minimise age-hardening, minimum binder contents may need to be controlled for example by adopting the “richness factor” concept
and by understanding more about the issue of aggregate-binder interaction.

29. Nevertheless..
Selecting good quality, more durable, bitumen in the first place will help to ensure a sustainable and durable asphalt mixture can be produced
Rheological testing is a very useful tool for preliminary assessment of bitumen quality

30. The Mapping Method
Revealed a distinctive distribution and localisation of materials with different performance
A useful preliminary screening tool for identifying the potential crack susceptibility of bituminous binders
Also potentially good for “forensic” analysis

31. THANK YOU