Identification and mechanical properties of asphalt mastic-aggregate interface transition zone (ITZ) based on nanoindentation and AFM

Document Type

Article

Publication Date

1-31-2025

Department

Department of Civil, Environmental, and Geospatial Engineering

Abstract

The asphalt mastic-aggregate interfacial transition zone (ITZ)，as a weak region in asphalt mixtures, is prone to stress concentration and subsequent fracture failure，thereby compromising the overall performance of mixtures. However, accurately identifying ITZ and characterizing its micromechanical behavior at the asphalt mixture scale remains challenging. This study aims to identify and characterize micromechanical behaviors of ITZ using nanoindentation (NI) and atomic force microscopy (AFM), meanwhile verifying the feasibility of AFM for testing asphalt mixtures ITZ. Four asphalt mixtures were prepared by mixing matrix and SBS-modified asphalt with basalt and limestone, respectively, and corresponding ITZ samples were obtained. ITZ was identified based on the load-depth curves, elastic modulus and indentation hardness obtained from NI testing. ITZ's microfracture properties were characterized using fracture toughness (KIC), and predictive models for KIC were developed. AFM was employed to analyze the microscopic morphology, DMT modulus, and adhesion of ITZ to identify and quantify its micromechanical properties. The results indicate that NI and AFM are effective in identifying ITZ, with NI excelling in quantifying the mechanical properties of ITZ, whereas AFM is better suited for identifying ITZ locations. ITZ's thickness and hardness are primarily determined by aggregates, while its elastic modulus and adhesion are influenced by asphalt mastic and aggregate. ITZ's thickness ranging from 6 to 12 μm for basalt-asphalt mastic and from 8 to 18 μm for limestone-asphalt mastic. The KIC obtained from NI testing effectively characterize the ITZ's resistance to crack propagation, with maximum and minimum values of 0.919 MPa·m0.5 and 0.711 MPa·m0.5, corresponding to ITZs formed by SBS-modified asphalt mastic-limestone and matrix asphalt mastic-basalt, respectively. The KIC prediction models proposed in this study exhibit a high correlation with elastic modulus and hardness, providing a reliable method to estimate the fracture resistance of asphalt mixtures.

Publication Title

Construction and Building Materials

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