1. The Influence of Air Void Content on Moisture
Damage Susceptibility of Asphalt Mixtures:
A Computational Study
Aikaterini Varveri, Cor Kasbergen & Tom Scarpas
Pavement Engineering, Delft University of Technology
Stavros Avgerinopoulos & Andy Collop
Faculty of Engineering, De Montfort University
CROW Infradagen 2014, The Netherlands, June 18-19, 2014

2. Moisture Damage in AC
 Moisture diffusion
 Advective transport
 Wheel loading
 Pumping action
COUPLING
Degradation of the cohesive strength
of the asphalt binder
Loss of the adhesion bond between
aggregate & asphalt binder
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study

3. Moisture Diffusion
( )
t

  

D   D e eij i j m ij
i,j
D a d
Molecular diffusion tensor
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study

  t
Normalized moisture concentration C /C
Fick’s Second Law

4. Influence of Air Voids on Moisture Damage
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study
  D e eij i j m ij
i,j
D a d
From literature:
 Moisture diffuses faster in air (Dair>Dbinder)
 Air void phase controls the rate of moisture diffusion into an
asphaltic mixture
 An association is found between moisture diffusion and the
interconnectivity of the voids
Past Modelling Efforts Problems
- Asphalt concrete was
modelled as a two-phase
material
- 2D finite element models
of asphalt concrete were
utilized
- Underestimate moisture
damage susceptibility
- Inability to distinguish
among different types of
mixtures (PA, SMA, etc.)

5. FE Micromechanical Meshes
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study
PA & SMA Mixtures
Mixture
Type
Nominal Maximum
Aggregate Size
(mm)
Binder Content
Pb (%)
Air Void
Content
(%)
Interconnectivity
of Air Voids
(%)
PA 10 4.4 23.7 90
SMA 10 6.4 5.3 10

6. Moisture Diffusion Analyses
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study
SMA Mixture
PA Mixture
1.00.0 θ

7. Moisture Diffusion Analyses
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study
0.00
0.20
0.40
0.60
0.80
1.00
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00
Normalizedmoistureconcentration
Specimen diameter (mm)
1 day
2 days
3 days
4 days
5 days
SMA Mixture
PA Mixture
A A’
A A’

8. T T T T
d d d d d¥ ¥ ¥ ¥= Þ = = =F F F C F F F F F F F C F
T T T T
e v v e e v v e v¥ ¥ ¥ ¥= Þ = = =F F F C F F F F F F F C F
Viscoelastic-Damage Energy Based Model
Multiplicative decomposition
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study

9. : 0  P FD
Viscoelastic-Damage Energy Based Model
Clausius-Planck Inequality
Rate of Internal
Mechanical Work
Free Energy Function
Ψ(F, ξ1, ξ2,…)
   ,v e dC C    
Helmholtz free energy function
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study

10. Moisture Damage Evolution Law
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study
1 (1 )(1 )md d d   
Total Damage Equation
(Kringos et al., 2011)

d
1.0
1.00.0
ˆd
1.0
0.0
 d f  
d
1
r
k W
md e 
 
1 a
d e 


 Moisture Damage
Mechanical Damage

11. Mechanical-Moisture Damage Analyses
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study
Dry specimen After 210 hrs of moisture diffusion
1.00.0 d

12. Moisture Concentration and Damage Distribution
Mechanical damage
Mechanical & moisture
damage
48 hrs of moisture
diffusion
1.0
0.0
θ
1.0
0.0
d
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study
1.0
0.0
d
SMA mixture PA mixture

13. Strength vs. moisture conditioning time
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study
SMA Mixture
PA Mixture
Moisture susceptibility parameter α1 >α2
21%
19 %
43 %

14. Conclusions
 Asphalt concrete is modeled as a three-phase material in three-
dimensions (3D) for the first time.
 The model is capable of predicting the degradation of the mechanical
performance of asphalt mixtures with increasing moisture content.
 The analyses confirm the well-known fact that AC mixtures with higher
air void content are more prone to moisture damage.
 Availability of the model enables assessing and ranking mixtures for their
moisture damage susceptibility.
The Influence of Air Void Content on Moisture Damage Susceptibility of Asphalt Mixtures: A Computational Study

15. Aikaterini Varveri, Cor Kasbergen & Tom Scarpas
Pavement Engineering, Delft University of Technology
Stavros Avgerinopoulos & Andy Collop
Faculty of Engineering, De Montfort University
CROW Infradagen 2014, The Netherlands, June 18-19, 2014
Thank you for your attention!