Page 335 - Mechanics of Asphalt Microstructure and Micromechanics

CHAPTER10

Digital Specimen and

Digital Test-Integration of

Microstructure into Simulation

10.1 Introduction
X-ray computerized tomography (XCT) imaging and computational simulation has
made it possible to characterize the properties of asphalt concrete (AC) through recon-
structing its three-dimensional (3D) microstructure and computational simulation
based on the 3D microstructure. The digital representation of the real 3D microstructure
(not a simulated 3D or 2D microstructure) of a physical specimen is called a digital
specimen. It is the digital counterpart of the physical specimen in every required detail.
A digital specimen is usually represented as a 3D digital image and naturally includes
scientific visualization of the initial/evolved microstructures and behavior related to
rutting, fatigue cracking, and thermal cracking. Figure 10.1a presents one digital speci-
men. It is a stack of 81 slices of a physical specimen non-destructively acquired. The
required details at particle level for mechanical modeling are available from the digital
specimen. Figure 10.1b represents a visualization of the void structure of the digital
specimen presented in Figure 10.1a. It is also a digital specimen if the study is on the
permeability and moisture damage of the asphalt mix. A digital specimen can be trans-
ferred through the Internet and shared by many researchers for use in multi-purpose
studies such as model verification and behavior simulation. With detailed representa-
tion of the microstructure of AC, modeling and simulation can be based on the real
microstructure of the material; experimental observation of the microstructure evolu-
tion can be compared with computational simulation to validate the models and the
understanding of the fundamental mechanisms of strength and deformation of AC.
Computational simulation of a mechanical test, which is based on digital specimens
and considers every required detail of the microstructure and its evolution, is called a
digital test. It is different from conventional computational simulations that assume
either a continuum model (Collop et al., 2003) or a simulated microstructure (Chang
and Meegoda, 1997, 1999; Buttlar et al., 1999; Buttlar and You, 2001; Bjorn et al., 2002;
Sadd et al., 2004). For example, Figure 10.1c presents a simulation of a triaxial compres-
sion test (digital test) on the digital specimen, while Figure 10.1d presents a simulation

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