Determination of Suitable Imaging Techniques for the Investigation of the Bonding Zones of Asphalt Layers

Abstract

The material behavior of asphalt depends on its composition of aggregate, bitumen, and air voids. Asphalt pavements consist of multiple layers, making the interaction of the materials at the layer boundary important so that any stresses that occur can be relieved. The material behavior at the layer boundary is not yet understood in detail, as further methods of analysis are lacking in addition to mechanical methods. For this reason, the layer boundary of asphalt structures was analyzed using imaging methods. The aim of this research was to find an imaging method that allows a detailed analysis of the bonding zone of asphalt layers. Two different imaging techniques were used for this purpose. One is a 2-D imaging technique (asphalt petrology) and the other is a 3-D imaging technique (high-resolution computed tomography). Image analysis is a widely used technique in materials science that allows to analyze the material behavior and their composition. In this research, attention was paid to the analysis of the position of the bitumen emulsion, because the contained bitumen is supposed to bond the layers together. It was found that the application of 2-D imaging (asphalt petrology) lacked the precision for a detailed analysis of the individual materials at the layer boundary. With high-resolution computed tomography, a detailed view is possible to visualize the individual materials at the layer boundary in 3D. However, it is difficult to differentiate the materials because there are no gradations in the gray values due to the identical densities. However, it is possible to differentiate between the bitumen from the asphalt and from the emulsion if a high-density tracer is added to the bitumen emulsion for the CT studies. The results of the investigations are presented in this article.

Investigation of the Permeability of Fibre-Modified Water Permeable Asphalt with Methods of Asphalt Petrology

“…For fibre, Afonso et al [17] reported an improved permeability after applying cellulose fibre, while Lyons et al [16] found a reduced permeability. Król et al [29] found that X-ray computed tomography (CT) could determine the permeability of asphalt based on the internal microstructure of PA. Middendorf et al [30] noted that CT is suitable only for highly specialized cases due to its cost, knowhow and equipment requirements.…”

Comparative Study of 2D Petrographic and 3D X-ray Tomography Investigations of Air Voids in Asphalt

“… CT-scan of an asphalt composite sample with a resolution of 42.9 µm: ( a ) 3D reconstruction of the sample which provides an overview of the measurement; ( b ) model of the entrapped air; ( c ) sectional view into the sample [ 18 ]. …”

“… The grinding process of asphalt petrology: ( a ) water-cooled grinder; ( b ) different grinding wheels; ( c ) specimen before and after grinding process; ( d ) surface of specimen after grinding process (epoxy resin is only left in the voids) [ 18 ]. …”

“…The computed tomography method is not exclusively used in science to observe void structurers. Middendorf et al [ 18 ] developed an analysis method for viewing the layer boundary of asphalt structures using CT. By adding tracers with high density, specific subareas in the asphalt specimen can be highlighted and viewed more closely with imaging. The procedure has mainly been used for analyzing bitumen emulsion at the layer boundary ( Figure 1 ).…”

The Position of Bitumen Emulsions on Different Bases

“…This made it possible to identify the bitumen emulsion in the subsequent analysis due to the difference in density. [9]. The (sprayed) samples were measured using a high-resolution µ-CT (type: Zeiss Xradia 520 Versa).…”