Electrical characterization of interfacial transition zone in concrete during freeze-thaw process

• Published in: Construction & building materials Vol. 425; p. 135960
• Main Authors: Wen, Juncheng, Sang, Yuan, Gao, Jinlin, Chen, Zhitao, Yang, Yingzi
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 26.04.2024
• Subjects: AC Impedance Spectrum; Composite effective conductivity; Conductive unit conduction path model; Freeze-thaw process; Interfacial transition zone; Conductive unit conduction path model; Freeze-thaw process; AC Impedance Spectrum; Composite effective conductivity; Interfacial transition zone
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2024.135960

The interfacial transition zones (ITZs) between aggregates and mortar are weak regions of concrete, which are more critical to the frost resistance of concrete due to a larger localized water-to-cement ratio. The effective conductivity of the ITZ was determined by separating electrical parameters in the AC impedance spectrum (ACIS), and the changes in microstructure within ITZ during the freeze-thaw (F-T) process were studied. First, based on the microstructure characteristics of Cement-Based Materials (CBMs), a circuit model of conduction path of conductive unit was established. The microstructure changes of CBMs during the F-T process (−50 °C to 10 °C) were characterized using ion conduction activation energy and the impedance of the constant phase element (CPE), which were classified into different regions in the F-T process. Circuit simplification and impedance parameters of CPE in different regions were analyzed. Subsequently, the composite effective conductivity formula (CECF) was proposed to separate the ITZ conductivity from the mortar or concrete conductivity. The relative change rate of conductivity during F-T process was used to define the freezing degree of CBMs, and the freezing degree of ITZ was calculated by CECF. The results indicated that in the F-T process of mortar and concrete, despite the volume fractions of ITZ being only 15.8% and 10.6%, its contribution to the freezing degree of the overall sample was 66%−70% and 57%−60%, respectively. This method can quantitatively characterize the effect of ITZ during F-T process and help understand the damage mechanism of F-T process. •A new equivalent circuit model in sub-zero temperature environments.•Characterization for freeze-thaw process by ionic conduction activation energy.•ACIS test identifies gel and capillary pores freezing.•Characterizing ITZs non-destructively and quantitatively during the freeze-thaw process.