{"title":"Computational simulation of alternating current (AC) impedance of hardened cement mortar","authors":"Qiwen Qiu","doi":"10.1016/j.electacta.2024.145412","DOIUrl":null,"url":null,"abstract":"<div><div>The present study proposes a novel methodology for simulating the AC impedance of hardened cement mortar, through the technology of micro computed tomography based finite element analysis (μCT-based FEA). Three-dimensional (3D) physical meso-scale structure of hardened cement mortar is first segmented into multicomponent phases of air void, cement paste, sand aggregate, and interfacial transition zone (ITZ) considered with different thicknesses. Then, the real structure of mortar after discretization is subjected to current harmonic perturbations to acquire its AC impedance spectra. Compared to traditional impedance measurement, the proposed simulation approach avoids the influence of external electrode and hence improves the characterization of cementitious electrochemical system in its true state. The simulated complex impedance presents a depressed high-frequency loop and varies with the increasing ITZ thickness in the range of 26.6 to 106.4 μm. The numerical impedance plots are fitted to a theoretical equivalent circuit model of <em>R<sub>s</sub></em>(<em>R<sub>ct</sub>Q</em>) consisting of bulk ionic resistance (<em>R<sub>s</sub></em>), charge transfer resistance (<em>R<sub>ct</sub></em>) at the solid/liquid interface, and non-Debye capacitance (<em>Q</em>). The changes in mesostructure of cement mortar with the thickened ITZs can be captured by a linear reduction of <em>R<sub>s</sub></em>, a non-linear decrease of <em>Q</em>, and a limited increase of <em>R<sub>ct</sub></em>. Based on the electrochemical impedance modelling, the study establishes the mathematical relationship between the defect's volume (air voids plus ITZ) and the model's parameters (<em>R<sub>s</sub></em> or <em>R<sub>ct</sub></em>) for prediction of material deterioration.</div></div>","PeriodicalId":305,"journal":{"name":"Electrochimica Acta","volume":"511 ","pages":"Article 145412"},"PeriodicalIF":5.5000,"publicationDate":"2024-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Electrochimica Acta","FirstCategoryId":"88","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0013468624016487","RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ELECTROCHEMISTRY","Score":null,"Total":0}
引用次数: 0
Abstract
The present study proposes a novel methodology for simulating the AC impedance of hardened cement mortar, through the technology of micro computed tomography based finite element analysis (μCT-based FEA). Three-dimensional (3D) physical meso-scale structure of hardened cement mortar is first segmented into multicomponent phases of air void, cement paste, sand aggregate, and interfacial transition zone (ITZ) considered with different thicknesses. Then, the real structure of mortar after discretization is subjected to current harmonic perturbations to acquire its AC impedance spectra. Compared to traditional impedance measurement, the proposed simulation approach avoids the influence of external electrode and hence improves the characterization of cementitious electrochemical system in its true state. The simulated complex impedance presents a depressed high-frequency loop and varies with the increasing ITZ thickness in the range of 26.6 to 106.4 μm. The numerical impedance plots are fitted to a theoretical equivalent circuit model of Rs(RctQ) consisting of bulk ionic resistance (Rs), charge transfer resistance (Rct) at the solid/liquid interface, and non-Debye capacitance (Q). The changes in mesostructure of cement mortar with the thickened ITZs can be captured by a linear reduction of Rs, a non-linear decrease of Q, and a limited increase of Rct. Based on the electrochemical impedance modelling, the study establishes the mathematical relationship between the defect's volume (air voids plus ITZ) and the model's parameters (Rs or Rct) for prediction of material deterioration.
期刊介绍:
Electrochimica Acta is an international journal. It is intended for the publication of both original work and reviews in the field of electrochemistry. Electrochemistry should be interpreted to mean any of the research fields covered by the Divisions of the International Society of Electrochemistry listed below, as well as emerging scientific domains covered by ISE New Topics Committee.