The influence of air void content on moisture damage susceptibility of asphalt mixtures: A computational study

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

Moisture Damage in AC

Moisture diffusion

Advective transport

Wheel loading

Pumping action

CO

UP

LIN

G Degradation of the cohesive strength

of the asphalt binder

Loss of the adhesion bond between aggregate & asphalt binder


Moisture Diffusion

( )t

D D e e

ij i j m iji, j

D a d

Molecular diffusion tensor


tNormalized moisture concentration C / C

Fick’s Second Law

Influence of Air Voids on Moisture Damage


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.)

FE Micromechanical Meshes


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

Moisture Diffusion Analyses


SMA Mixture

PA Mixture

1.0 0.0 θ

Moisture Diffusion Analyses


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

No

rma

lize

d m

ois

ture

co

nce

ntr

ati

on

Specimen diameter (mm)

1 day

2 days

3 days

4 days

5 days

SMA Mixture

PA Mixture

A A’

A A’

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


: 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


Moisture Damage Evolution Law


1 (1 )(1 )md d d

Total Damage Equation

(Kringos et al., 2011)

d

1.0

1.0 0.0 ̂

ˆd

1.0

1.0 0.0

d f

d

1rk W

md e

1 ad e

Moisture Damage

Mechanical Damage

Mechanical-Moisture Damage Analyses


Dry specimen After 210 hrs of moisture diffusion

1.0 0.0 d

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


1.0

0.0

d

SMA mixture PA mixture

Strength vs. moisture conditioning time


SMA Mixture

PA Mixture

Moisture susceptibility parameter α1 >α2

21%

19 %

43 %

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.


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!