Progress in Engineering Computational Technology
Chapter 8 R. Lackner*, R. Blab+, A. Jäger*, M. Spiegl+, K. Kappl+, M. Wistuba+, B. Gagliano+ and J. Eberhardsteiner*
Christian Doppler Laboratory for "Performance-Based Optimization of Flexible Road Pavements" *Institute for Strength of Materials, +Institute for Road Construction and Maintenance, Vienna University of Technology (TU Wien), Austria Keywords: multiscale, homogenization, micromechanics, creep, fatigue, asphalt, bitumen, pavement.
A reliable assessment of the performance of
multi-composed materials requires
suitable procedures and models for the evaluation of key material properties.
In case of asphalt used for trafficked pavements,
these key properties reflect its
resistance to rutting caused by thermal deformation, to cracking at low
temperatures, and to fatigue failure under repeated load cycles.
Asphalt is composed of bitumen,
aggregate, and air voids, showing a complex thermo-rheological behavior.
E.g., the low viscosity
of asphalt at high temperatures (
 mm), and (iv) the asphalt-scale (mortar + aggregate with  mm),
see Figure 1.
Within each observation scale,
the characteristics (such as structure and material properties)
of the constituents
present at this scale are taken into account. Moreover, changes in scale characteristics,
resulting from mechanical loading and/or environmental conditions may be
considered at the respective scale of observation.
The goal of the multiscale model presented in this paper is the determination of macroscopic material parameters which serve as input for the analyses of flexible pavements. These parameters are obtained by means of upscaling procedures, bridging the scales from the bitumen-scale to the macroscale. For the assessment of the used upscaling techniques, herein formulated in the framework of continuum micromechanics, so-called verification experiments are required in addition to indentification experiments. The latter are used for identifying material characteristics at the different scales of observation. Following this hybrid character of the research work, comprising theoretical work regarding the development of appropriate upscaling techniques and experimental work for either identification or verification, upscaling of three key properties of asphalt, describing (i) low-temperature creep, (ii) thermal conductivity, and (iii) microcracking, is presented. These properties determine the risk of both cracking in consequence of thermal dilation during temperature changes and fatigue failure under repeated loading. By establishing the upscaling scheme for key properties of asphalt, i.e., having related this key properties to the mixture characteristics of the asphalt and the behavior of the constituents, performance-based optimization of flexible pavement structures can be achieved.
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C) is a necessary prerequisite
during the construction and compaction process of high-quality asphalt layers.
When the surface temperature reaches
C during hot summer periods,
however, this viscosity should be significantly higher in order to
minimize the development of permanent deformations (rutting).
The desirable increase of
viscosity and, hence, increase of stiffness with decreasing temperature
at hot and medium temperatures (
C)
are, on the other hand,
disadvantageous at low temperatures (
C), causing low-temperature
cracking in asphalt pavements. This optimization problem concerning the behavior
of asphalt at different temperature regimes is a main objective of the Christian
Doppler Laboratory "Performance-Based Optimization of Flexible Road Pavements"
(TU Wien), headed by Ronald Blab. For the optimization process of a multi-composed
material such as asphalt, three different modes can be distinguished:
