Fractal and multifractal characteristics of three-dimensional meso-structure for asphalt mixture

Abstract

The aggregate skeleton and void structure in the asphalt mixture are critical and highly correlated to the mechanical performance of the pavement. However, the extreme heterogeneity and complexity bring devastating difficulties to characterizing and analyzing the mixtures' mesostructure. Therefore, this study aimed to propose a novel depicting scheme accounting for the size distribution and spatial arrangement of the mixtures' components utilizing the fractal and multifractal analysis. Two compaction methods (Marshell and Superpave) and three design indexes (gradation, NMAS, and compaction work) were adjusted to prepare the samples, which were then scanned and digitally reconstructed. The fractal dimension (D) and related multifractal indicators (i.e., Δα and Δf(α)) were determined and applied to quantitative assess the structural changes. Finally, the relationships of design indexes to fractal and multifractal behaviors were comprehensively discussed. Results indicate that fractal and multifractal theories are feasible in describing the heterogeneous particle skeleton and void structure in the asphalt mixture. Firstly, the multifractal approach was proven to allow a more informative characterization of 3D systems than simple fractal theory. Moreover, the excellent correlation between the design/construction and fractal/multifractal indicators has been confirmed for asphalt pavement. Overall, the fractal and multifractal indicators enriched the options for microstructural evaluation, which will be conducive to revealing the relationship between the microstructural characteristics and mechanical performance of the asphalt mixture.