Internal structure characterization of asphalt mixtures for rutting performance using imaging analysis

TLDR

Two‑dimensional imaging of asphalt concrete microstructure is an economical approach, yet prior studies have mainly focused on simple aggregate analyses, despite the aggregate internal structure being crucial for rutting resistance. This study introduces a detailed internal‑structure characterization method and proposes new indices to link asphalt mixture structure to rutting resistance. The authors defined contact‑point, contact‑length/area, and contact‑plane‑orientation parameters for both total aggregates and the load‑bearing skeleton, and processed images of mixtures with varying gradations, binders, modifications, and compaction using a modified image‑analysis software. The developed indices—aggregate‑on‑aggregate contact points, contact length/area, and contact plane orientation—capture the internal structure and correlate with rutting performance, while also reflecting the effects of compaction, gradation, and binder modification.

Abstract

Characterization of the asphalt concrete microstructure using two-dimensional (2-D) imaging techniques is an economically efficient approach. However, the features that have been captured and quantified using 2-D imaging in most published research have been limited to simplistic analyses of aggregate structure. The present research focused on introducing a more elaborate method of characterization of internal structure, and proposing new indices to relate to and explain rutting resistance performance of asphalt mixtures. The aggregate internal structure provides the skeleton of the asphalt concrete, which plays an important role in rutting resistance. It is shown that this structure can be captured using a combination of image analysis indices developed in this research, namely: number of aggregate-on-aggregate contact points, contact length/area, and contact plane orientation. These parameters are defined for both the total aggregates and for the effective load bearing aggregate structure, referred to as the 'skeleton' in this study. Software developed in a previous study and significantly modified for this paper, is used to process digital images of a set of asphalt mixtures with different gradations, binder contents, types of modification, and compaction efforts. The results demonstrate a correlation between the internal structure indices and the mixture rutting performance. Additionally, the indices were successfully used to capture the effect of compaction effort, gradation quality, and binder modification on the mixture internal structure.