This document discusses the goals and methodology of a PhD project investigating the healing of asphalt mortar using an American healing model approach. The project aims to formulate a fundamental healing model based on healing mechanisms and material parameters that can rank the healing performance of asphalt mortars using experimental results. It provides background on previous research on asphalt healing and reviews the Texas A&M healing model. The convolution approach of this model will be adopted to separately analyze the contact surface and strength development processes. Next steps include creating cracks in samples, measuring strength and stiffness over time under varying pressures, and using tomography to measure the development of contact area during healing.

1. 1Challenge the future
Healing of asphalt mortar
An investigation into the possibilities of the American
healing approach
Infradagen 2014
Greet Leegwater, Tom Scarpas and Sandra Erkens

2. 2Challenge the future
Content
• Aim of the PhD project
• Literature review:
• the Texas A&M healing model
• Fit of the model / approach to literature
• Next steps

3. 3Challenge the future
Research motivation
• Bazin and Saunier first systematically studied healing of
asphalt.
• Asphalt heals, to what extend depends on the material, the
damage, time, temperature, and pressure.
• In most design guidelines healing is incorporated based on
own experience and assumptions.
• For innovative mixtures healing parameters are expected to
be different, however there is no method to determine a
healing parameter based on material performance.

4. 4Challenge the future
Goal
• Formulate a fundamental healing model, based on healing
mechanisms and driving material parameters, that can rank
healing performance of asphalt mortars using experimental
results.

5. 5Challenge the future
Literature review; the Texas A&M
healing model
• Little and Bhasin adopted healing from polymers (Wool and
O’ Conner).
• Recovery of mechanical properties is the sum of two
functions
• Wetting distribution function (part of surface in contact)
• Intrinsic healing function (load bearing capacity of surfaces in contact)
• The function shows how healing (R) is a convolution of
wetting (𝜙(𝜏,X)) and intrinsic healing (Rh) functions.
• R is 1 if all damage is healed and 0 if no damage is healed.
( ,X)
( )
t
h
d
R R t d
d


 
   


6. 6Challenge the future
Example healing curve according
to the model
20%
40%
60%
80%
100%
time
Rh
R0

7. 7Challenge the future
Wetting function [Little and Bhasin]
•

8. 8Challenge the future
Intrinsic healing function [Bhasin,
Palvadi et al. 2011]
•

9. 9Challenge the future
Two piece healing method
• Qiu (2012) demonstrated that this method was dependant on
pressure level: no real intrinsic healing.

10. 10Challenge the future
Match of the model with literature
• The model matches well with observed impact of
temperature, pressure and time, versus material parameters.
• The approach matches with the observed healing in softer
materials.
• There is also room to incorporate adhesion differences in
materials.
• The separate analyses of contact surface, could be the key to
explain differences dependant of test methods.
• The seperate analyses of contact surface and strength
development might explain quick recovery of stiffness.

11. 11Challenge the future
Conclusions convolution model
• The convolution approach will be adopted, as the separation
of the two different processes is expected to increase the
fundamental insight in the healing mechanism.
• The presented formula’s for wetting and intrinsic healing will
not be adopted, as there is no convincing evidence to support
these models.

12. 12Challenge the future
Next steps
• Create a crack, measure
strenght and sitffness.
• Place two halves togehter
under different pressures.
• Measure healing strength at
different moments in time.
• Use tomography to measure
development of contact
area.
t = 0
Contact area = 0
t = t1
Contact area = 10%
t = t2
Contact area = 60%
t = ?
Contact area = 100%