Microstructure Study of WesTrack Mixes from X-Ray Tomography Images

Abstract

Asphalt concrete is a composite comprised of aggregates, air voids (AVs), and microcracks of various sizes and shapes. The property of asphalt mixes is not only affected by volume fractions of these components such as voids in mineral aggregates (VMA, the complementary volume fraction of aggregates) and AV content but also the size and spatial distributions of these components. However, conventional and Superpave volumetric mix designs specify only bulk values of VMA and AV, which may not be able to capture all the critical factors of a mix. The unexpected WesTrack mixes’ premature failure may reflect this limitation in design specifications. Results are presented of a study to evaluate statistically the spatial and size distribution of the void systems of the mixes and to find other possible parameters that might be better or complementary to the current parameters to characterize the mixture internal structure and performance. Void systems of three original WesTrack mixes were evaluated using X-ray tomography images and stereology methods. The spatial void content variation and void size distribution for six specimens of three mixes were quantified. Specific damaged surfaces (void surfaces were considered damaged surfaces because they do not transmit forces), damage tensor, mean solid path among damaged surfaces, and mean solid path tensor, which indicate damage level and interaction of the damage, were also quantified. It was concluded that coarsegraded mix is more severely inherently damaged and that this set of parameters gave a performance ranking of the three mixes consistent with field observations. Moreover, quantified tensors are applicable in continuum damage mechanics for fatigue and rutting modeling.

Air Void Distribution of Asphalts Determined by Computed Tomography

“…In recent years, CT imaging has been increasingly extended to the structural characterization of asphalt concrete [5,8,9], cement concrete [10,11], and rock [12,13]. It can be used to reconstruct the 3D structure of a sample for computer simulation of the performance of the material under various loading and environmental conditions.…”

“…Meanwhile the sample is still intact and can be used for other nondestructive or destructive macro property tests such as strength or modulus tests. Therefore CT is one of the most effective tools to study the microstructure-macro property relation [9]. In computed tomography X-rays from a well collimated source refers to the cross-sectional imaging of an object from either transmission or reflection data collected by illuminating a slice of the object or patient from many different directions.…”

Characterization of Asphalt Materials Using X-Ray High-Resolution Computed Tomography Imaging Techniques

“…Several investigators have illustrated the use of CT scans for the nondestructive evaluation of soils (Petrovic et al 1982;Aylmore and Hainsworth 1983;Alshibli et al 2000;Halverson et al 2005). CT imaging has gained increasing applications in civil engineering materials research in recent years (Braz et al 1999;Shashidhar 1999;Hall et al 2000;Wang et al 2001;Masad and Button 2004;Wang et al 2004b).…”

“…This phenomenon was strongly noticed at high compaction efforts. Wang et al (2001) evaluated the void systems of three original WesTrack mixes using CT images and stereology methods. A forensic analysis of Arizona's US-93 Superpave sections using CT images revealed that the void structure contributed significantly to the distress of these sections .…”

An Evaluation of the Stress Non-Uniformity Due to the Heterogeneity of AC in the Indirect Tensile Test

“…X-ray Tomography is a valid tool for quantifying the microstructure of asphalt concrete (Wang et al 2001;Masad et al 2002;Wang et al 2004). The asphalt concrete sample was scanned using x-ray tomography to obtain a series of gray image slices that reflect density variation of the constituents such as asphalt binder, aggregates and voids (Figure 1).…”