Computational modelling of heterogeneity of asphalt mixtures - - PowerPoint PPT Presentation

Daniel Castillo 31.05.2018 Transport Research Finland 2018

Computational modelling

• f heterogeneity of

asphalt mixtures

AC Heterogeneity

• AC: Mixture and compaction of

bitumen, aggregates and air voids. Heavily used in construction of road infrastructure, enduring traffic loadings and environmental conditions.

• Differences among AC constitutive

phases’ response to mechanical and environmental solicitations.

• AC is a heterogeneous material, and

this heterogeneity may induce variability in the response.

Aggregates Air voids Fine Aggregate Matrix (FAM)

Initial considerations

“Macro” approaches

A random field is a n-dimensional vector of random values that exhibit spatial correlation.

Correlated random field, isotropic. Uncorrelated random normal numbers.

3.02

• 3.23

Three dimensional random field, isotropic

CASTILLO & CARO (2014). “Effects of air voids variability on the thermo-mechanical response of asphalt mixtures”

AC Heterogeneity – “Macro”

Random fields

AC Heterogeneity – “Macro”

Methodology

Field of horizontal strains (εh)

• 3.08

3.18

εh ×10-4

Random field of Air Voids

4.43 10.07

AV [%]

Calculated Linear Viscoelastic properties

6200 11,900

Eo [MPa] Air Voids LVE Strain (εh) CASTILLO & CARO (2014). “Probabilistic modeling of air void variability of asphalt mixtures in flexible pavements”

AC Heterogeneity – “Macro”

Air Void content 5.9 % AV 6.6 % Average AV content 6.45 % AV 7.4 % AV 6.68 % AV 7.06 % AV 7.44 %

AC layer 1 AC layer 2 AC layer N AC layer 3

AV 8.3 %

Computational applications

AV [%]

1.3 14.8 8.1 11.4 4.7 CASTILLO & CARO (2014). “Probabilistic modeling of air void variability of asphalt mixtures in flexible pavements”

1.0E-04 1.2E-04 1.4E-04 1.6E-04 1.8E-04 98 100 102 104 106 108 110

εh

x [cm]

Bottom row

x

Homogeneous layers

AC Heterogeneity – “Macro”

Computational applications

CASTILLO & CARO (2014). “Probabilistic modeling of air void variability of asphalt mixtures in flexible pavements”

1.0E-04 1.2E-04 1.4E-04 1.6E-04 1.8E-04 98 100 102 104 106 108 110

εh

x [cm]

Bottom row

x

Heterogeneous layers

AC Heterogeneity – “Macro”

Response dispersion increases (approx. x8)

Computational applications

CASTILLO & CARO (2014). “Probabilistic modeling of air void variability of asphalt mixtures in flexible pavements”

AC Heterogeneity – “Macro”

Heterogeneous FE model of the pavement structure

Eo [GPa]

20.7 45.9 33.3 39.6 27.0

Area of moving load application

× N

x y z

Heterogeneity in the asphalt material (3D RF)

Computational applications

CASTILLO & AL-QADI (2018). “Importance of Heterogeneity in Asphalt Pavement Modeling”

AC Heterogeneity – “Macro”

Computational applications

AC layer – Top view

x y z

×

7.83 με CV 5.6% CASTILLO & AL-QADI (2018). “Importance of Heterogeneity in Asphalt Pavement Modeling”

AC layer – Bottom view

×

x y z

std(E11) [με]

0.00 9.00 3.17 6.08 0.25

7.83 με CV 6.58%

“Micro” approaches

AV content Aggregate fraction

AC Heterogeneity – “Micro”

Random generator of microstructure (MG)

CASTILLO, CARO, DARABI & MASAD (2015). “Studying the effect of microstructural properties on the mechanical degradation of asphalt mixtures”

MG

2D specimen shape Gradation Random 2D asphalt concrete microstructure

AC Heterogeneity – “Micro”

Random generator of microstructure (MG)

CASTILLO, CARO, DARABI & MASAD (2015). “Studying the effect of microstructural properties on the mechanical degradation of asphalt mixtures”

Random 2D asphalt concrete microstructure

AC Heterogeneity – “Micro”

Random generator of microstructure (MG)

t = 150 s t = 225 s t = 300 s

Pavement Analysis using Nonlinear Damage Approach

DAMAGE DENSITY, Φ

0.00 2.53 1.26 1.89 0.62 CASTILLO, CARO, DARABI & MASAD (2015). “Studying the effect of microstructural properties on the mechanical degradation of asphalt mixtures”

28.11 mm² 10 20 30 40 50 60 70 80 100 150 200 250 300 Damaged FAM area [mm²] Time [s]

NMAS 12.5 mm 4% Air voids

43.00 mm² 10 20 30 40 50 60 70 80 100 150 200 250 300 Damaged FAM area [mm²] Time [s]

NMAS 12.5 mm 7% Air voids

31.89 mm² 10 20 30 40 50 60 70 80 100 150 200 250 300 Damaged FAM area [mm²] Time [s]

NMAS 19.0 mm 4% Air voids

48.50 mm² 10 20 30 40 50 60 70 80 100 150 200 250 300 Damaged FAM area [mm²] Time [s]

NMAS 19.0 mm 7% Air voids x100 specimens x100 specimens x100 specimens x100 specimens

AC Heterogeneity – “Micro”

Random generator of microstructure (MG)

CASTILLO, CARO, DARABI & MASAD (2015). “Studying the effect of microstructural properties on the mechanical degradation of asphalt mixtures”

x100 x100

Materials in nature are heterogeneous. Artificial materials, even more! We need to study and include this heterogeneity as an intrinsic part of our computational models.

In summary…

What did we do?

We considered AC heterogeneity implicitly/explicitly into our computational models.

Why did we do it?

Heterogeneity has an important, measurable effect on the variability of material response. This is particularly true for a material as highly heterogeneous as asphalt concrete. Uncertainty data on mechanical properties/response is traditionally scarce.

What can we do with it?

• Several applications come to mind. In the previous modelling studies we just generated hundreds (!) of specimens, at

random, with a degree of ‘control’ over properties that only a computer can provide. This can be seen as an alternative to complement the laboratory work, which requires resources (effort, time and materials – money). Also, traditional as well as non-traditional materials and mechanical properties can be tested (RAP , aged materials, aggregate shapes). Some sources call this “virtual laboratory”.

• Apart from the previous modelling studies, it is possible to apply the tools when developing specifications, and for

quality control.

• We can estimate new data on uncertainty in response, which is difficult or sometimes impossible to obtain in the

laboratory or the field.

• The tools provide a framework for approaching the modelling of heterogeneity to any existing/new materials; they

have applicability to a variety of infrastructure and building materials.