1 Challenge 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 Challenge 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 Challenge 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 Challenge 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 Challenge 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

dR R t d

d

6 Challenge the future

Example healing curve according

to the model

20%

40%

60%

80%

100%

time

Rh

R0

7 Challenge the future

Wetting function [Little and Bhasin]

•

8 Challenge the future

Intrinsic healing function [Bhasin,

Palvadi et al. 2011]

•

9 Challenge the future

Two piece healing method

• Qiu (2012) demonstrated that this method was dependant on

pressure level: no real intrinsic healing.

10 Challenge 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 Challenge 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 Challenge 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%