A review on microstructural characterization of cement-based materials by AC impedance spectroscopy

Cement and Concrete Composites 100 (2019) 1–14

Contents lists available at ScienceDirect

Cement and Concrete Composites journal homepage: www.elsevier.com/locate/cemconcomp

A review on microstructural characterization of cement-based materials by AC impedance spectroscopy

T

Xiang Hua,b, Caijun Shia,∗, Xiaojin Liua, Jiake Zhanga, Geert de Schutterb a Key Laboratory for Green & Advanced Civil Engineering Materials and Application Technology of Hunan Province, College of Civil Engineering, Hunan University, Changsha, 410082, PR China b Magnel Laboratory for Concrete Research, Department of Structural Engineering, Ghent University, Ghent, B-9052, Belgium

A R T I C LE I N FO

A B S T R A C T

Keywords: AC impedance spectroscopy Equivalent circuit model Hydration Microstructure Chloride induced corrosion

As a non-destructive method, AC impedance spectroscopy is a promising technique for the characterization of cement-based materials owing to its advantages in real time monitoring. In this paper, the equivalent circuit models in publications applied for different cement-based systems are summarized. The determinations of hydration properties, microstructural changes and chloride induced corrosion parameters of cement-based materials by AC impedance spectroscopy measurements are reviewed. With some appropriate models, the AC impedance parameters can be applied to characterize microstructure and interfacial properties of cement-based materials. The experimental condition control and data analyses are discussed. Some improvements for measurement device and development of equivalent circuit models for different kinds of binding materials are needed.

1. Introduction AC impedance spectroscopy is a non-destructive technique, which can be used to monitor the hydration and structural development of cement-based materials. After being firstly used to study the electrochemical properties of cement pastes by McCarter [1] in 1988, AC impedance technique has been widely applied in investigating early hydration, microstructural evolution and corrosion behavior of cementbased materials [2–5]. Due to the limit of testing device, the measurements at the very initial period were conducted over a limited frequency range, nearly kilohertz [6–8]. With the development of electrical measurement techniques, electrical impedance characteristics within high-frequency range could be revealed [9–11]. It has been demonstrated that AC impedance spectroscopy is a promising technique for revealing the variation of pore structure and ionic conductivity during the hydration of cement-based materials. The impedance spectra are a group of plots representing the measured AC impedance data, among which Nyquist plot is mostly used. In a Nyquist plot, the real and imaginary impedances are expressed in horizontal and vertical axes respectively and different circles and/or lines may be shown within different frequency ranges in the plots. In general, a typical impedance spectrum for cement-based materials consists of a high and low frequency arcs, characterizing the bulk materials effect and polarization effect of electrode/specimen respectively

∗

[12]. As shown in Fig. 1, the low frequency line can be treated as a large-diameter arc and a fairly complete low frequency arc can be obtained when testing frequency reaches as low as 10−6Hz and the complete high frequency arc may be obtained at various frequencies with different geometries of samples as shown in Fig. 1(a) [13,14]. Some researchers attributed the high-frequency capacitive loop in impedance spectrum to the dielectric response of cement-based materials [2,3]. However, a dielectric constant considerably larger than that of ceramic materials was obtained with this consideration [3,4]. In some studies [15–17], the bulk and interfacial contributions of cement pastes on electrical response were separated by non-contacting method, and the high frequency loop was explained by two constants associated to the solid phase and the electrolytes in the pore solution. The establishment of equivalent circuit models is important for the analysis of impedance results and has broadened the applications of this technique. With an appropriate electric circuit, information on the microstructure and interfacial properties of the testing samples can be extracted from the measured impedance spectrum. Xu and Gu et al. [18–23] established relationships between impedance characteristics and concentration of pore solution, porosity and mean pore size, which could be used to reflect the hydration degree and microstructural evolution of cement-based materials. Mineral admixtures, temperature, moisture conditions and mechanical loading on microstructure can affect the electrical properties of hardened cement-based materials

Corresponding author., E-mail address: [email protected] (C. Shi).

https://doi.org/10.1016/j.cemconcomp.2019.03.018 Received 3 May 2018; Received in revised form 19 August 2018; Accepted 18 March 2019 Available online 21 March 2019 0958-9465/ © 2019 Published by Elsevier Ltd.

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

Fig. 1. The theoretical (a) and measured (b) Nyquist plot from AC impedance spectroscopy.

the conductive paths within specimens. Song [7] proposed an equivalent circuit model for concrete samples based on a simplified microstructure model of concrete. In this model, continuous, discontinuous and “insulator” conductive paths were applied to express the roles of different phases play in AC impedance behavior. The determination of an appropriate equivalent circuit is the most important step for the analysis of impedance spectrum. In a typical Nyquist plot of cement-based materials, several capacitive loops are found and every ideal loop can be simulated with a parallel series of resistor and capacitor. Table 1 summarizes the equivalent circuit models in publications. They can be classified into four categories: (1) models based on simulation approaches; (2) microstructure-based models; (3) models for materials with mineral admixtures or conductive materials; and (4) chloride migration models. The following sections will discuss these models in detail.

[24–26]. Impedance spectroscopy can also be used to study the durability of cement-based materials such as chloride ion permeability, freeze-thaw, creep, carbonation and steel corrosion resistance [27–30]. Recently, AC impedance spectroscopy was used to evaluate the fiber orientation in plant fiber-cement composites and the results indicated that this technique was a reliable non-destructive tool [31]. An et al. [32] investigated the impedance characteristics of ternary cementitious materials and determined the composition with the highest impedance so to reduce electrochemical corrosion of steel embedded in concrete caused by stray current. This paper reviews those published equivalent circuit models for different cement-based materials firstly, then summarizes the applications of AC impedance spectroscopy in studying hydration and microstructure, and determining chloride migration and corrosion parameters of cement-based materials. Discussions on experimental condition control and experimental result analyses are provided finally. Studies on steel corrosion or properties of other conductive materials by AC impedance spectroscopy have been extensively conducted, while this study mainly reviewed the publications in recent two decades on characterization of cement-based materials. It is hoped that this paper may provide some useful information for the further study of microstructural and interfacial properties characterization and durability evaluation of cement-based materials by AC impedance spectroscopy techniques.

2.1. Models based on simulation approaches Due to the complicated composition and inhomogeneous microstructure, it is difficult to model different types of cement-based material with one electric circuit. Moreover, the existence of the solidliquid interface may significantly affect the electrical response of the tested sample. Therefore, when determining an equivalent circuit model, researchers may propose several different models based on their understanding of the characteristics of material and consideration of reasonable simplification, finally find one that fits the experimental results best. For some complicated materials, the dispersion effect due to the roughness of the solid-electrode surface or some other unpredictable factors may make it difficult to find an appropriate circuit model including only resistor, capacitor and inductor [36]. The application of constant phase angle element (CPE) may help to solve this problem. A CPE element equals to a distributing parameter circuit, and can be treated as an imperfect capacitor. In a Nyquist plot, the parallel connection of a resistor and CPE represents an arc whose center point deviates from the x axis. The impedance of a CPE can be expressed as follows:

2. Equivalent circuit models for cement-based materials In the AC impedance spectrum (Nyquist plot), it can be qualitatively analyze the evolution of the shape and turning points with the hydration of cement-based materials. However, it's nowhere near enough for understanding the microstructural development and interfacial properties of cement-based materials. Generally, complicated electrochemical systems form within cement-based materials when imperceptible electrical voltages are applied, which can be expressed by parallel or series connection of resistor, capacitor and/or inductor. Within cement-based materials, solids and liquids with different chemical and mineral components are formed and placed, which can reveal different electrical properties and be expressed by different electrical elements. Due to the complicated microstructure of cement-based materials, it's impossible to use a circuit model to fully represent the electrical properties of a sample. Then, some simplified physical models were proposed and the equivalent circuit model can be established based on these physical models. During the studies on electrical properties of cement-based materials, cell model [33], brick model [27], T and I models [20] and barrier-hole model [34] were proposed and used to explain the contribution of solids, liquid and solid-liquid interface to the AC impedance behavior of testing samples. However, some unreasonable results were also obtained. In 1994, McCarter [35] firstly proposed the idea of modelling the cement-based materials according to

Z=

1 −n nπ 2π ω ⎛cos − jsin ⎞ Y0 2 2 ⎠ ⎝

(0 < n < 1)

(1)

where, Y0 (=1/Q) and n are parameters of CPE. The value of n relates to the deviation of CPE from pure capacitance. When n = 1, the CPE can be described by a single time-constant element and the parameter Q has the unit of capacitance; otherwise, the unit of Q is sn/Ω cm2 or Fsn−1/cm2. Poupard et al. [37] used an equivalent circuit model consisting of CPE elements to study the threshold chloride concentration of steel corrosion. However, the meanings of the circuit parameters except the polarization resistance were not explained. In 1991, Scuderi et al. [38] proposed an equivalent circuit model 2

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

Table 1 Summary of different equivalent circuits in literature. Classifications

References

Models based on simulation approaches

Scuderi [38]

The relationship between element parameters and microstructure of cement pastes is lacking.

Poupard [37]

Rp is the polarization resistance

MacPhee [41]

CP, BP, HP and UC represent the continuous electrolyte-filled pores, the discontinuous or blocked electrolyte-filled pores, the hydration products, and the unreacted cement respectively.

Xie [20]

R0 is the resistance of solid and liquid phases while R1 and C1 are the resistance and total capacitance of solid-liquid interfaces respectively.

Andrade [15]

C1 is the dielectric capacitance related to solid phase,R2 is the resistance of electrolyte filling pores, C2 relates to the chemistry of electrolyte inside pores.

Song [7]

C1 is the dielectric capacitance related to the continuous concrete matrix, R2 and R3 are the resistance of pore solution in the continuous and the discontinuous conductive paths, C3 is a double parallel plate capacitance related to the discontinuous cement paste layers in concrete.

Cruz [9]

R1 is the resistance of electrolytes in connected pores,CPE2 is the electrical double layer formed at solid-solution interface in the connected pores, capillary and gel pores of C-S-H,R3 and CPE3 are the resistance of solution and the ion diffusion in or near C-S-H gel pore respectively.R0 and CPE0 are related to the impedance of the electrode-solution interface.

Woo [8]

Rp is the resistance of particles or fibers, Rmv and Cm are the resistance and capacitance of matrix phase, Rm' and Cm' are the resistance and capacitance increased by insulating particles, Rm'' and Cm'' are the compensation resistance and capacitance for the increased R and C by Rm' and Cm',Rc' and Cc' are the resistance and capacitance of passive oxide film at fiber coating, Rc and Cc are the resistance and capacitance related to electrode polarization effect

Shi [45]

Rs is the resistance of electrolyte, Cd accounts to capacitance of the electrode/electrolyte interface. Faradaic impedance ZF here is used to characterize the reaction kinetics and diffusion, which is composed of the resistance of charge transfer Rct in series with the so-called Warburg impedance ZW describing the diffusion behavior.

Sánchez [10]

R0 is the resistance of electrolytes between the impedance spectroscopy measuring electrodes and the sample, R2 and R3 are resistances attributed to the ionic motion in percolating pores and in occluded pores respectively, C1 is the dielectric capacitance related to solid fraction, C3 is an ionic double layer capacitance at the pore walls-inner concrete electrolyte interface, Re and Ce are the resistance and capacitance associated with the system external electrolytes-concrete interfaces.

Microstructure-based models

Cement-based materials with mineral admixtures or conductive materials

Chloride migration models

Equivalent circuit

Description

In order to investigate the corrosion of steel at different stages, Ismail et al. [39] used four equivalent circuit models proposed by other researchers for different samples via electrical fitting. They studied the evolution of bulk resistance of concrete attacked by chloride ions. However, different circuit elements applied in these models make it

corresponding to the impedance spectrum of cement pastes after 69 h of hydration. In this spectrum, two distinct high frequency arcs appeared. They adopted a series connection of R/C network and a CPE to represent the electrode/specimen interface effect. It also failed to make clear the physical meanings of the circuit elements in this study. 3

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

difficult to evaluate other electric parameters. Ribeiro and Abrantes [40] summarized the electrical circuit elements corresponded to different physical processes involved in steel corrosion including charge transfer, electrical double layer, adsorption and mass transport and analyzed the impedance measurement results with different equivalent circuit models. Generally, the models proposed based on general simulation approaches may be practicable to explain an obtained impedance spectrum and to obtain some reasonable correlations between electrical responses and microstructure of a sample. However, there is some subjectivity in application of these methods and it's difficult to obtain the physical meanings of circuit elements by using these models. 2.2. Microstructure-based models In 1996, Macphee et al. [41] firstly presented an equivalent circuit model with priority to the microstructure of cement-based materials. In this model, the potential conductive paths were taken into consideration and actual physical meanings of the circuit parameters were also studied. Nevertheless, this equivalent circuit was extremely complicated due to the consideration of all conductive paths of connected and unconnected pores, hydration products and unreacted cement. Since the principal and unimportant conductive paths were mixed, it was difficult to extract values of resistance and capacitance from individual microstructural properties, which limited the application of the model. Xie and Gu et al. [18,20] regarded the major contribution of AC impedance characteristics of cement-based materials from the solid-liquid interfaces and proposed a “brick model”. They quantitatively studied the relationship between impedance spectrum parameters and microstructure of cement pastes. In their research, a dielectric amplification factor was used to explain the obtained larger dielectric constant than the habitual values for portland cement paste. Andrade et al. [15] proposed an equivalent circuit model for the experiment results by non-contact method. In the model, the electrical elements related to the interface effects were absent due to the noncontact between samples and electrodes. This equivalent model successfully differentiated the influences of solid phase and electrolyte filled pores on impedance spectrum and greatly promoted the analysis of impedance data. Cabeza et al. [25] improved Andrade's model by adding an extra series of resistor into the model to express the ionic motion in crossing pores or between samples and electrodes. This model laid a good foundation for the subsequent studies of equivalent circuit models. In the electrical circuit model proposed by Song et al. [7], only the major conductive paths such as the continuous conductive paths, the discontinuous conductive paths, and the “insulator” conductive paths were considered (see Fig. 2). Meanwhile, they tried to interpret the effects of hydration time, silica fume replacement and water to cement ratio on the high frequency arc by this model [5]. The microstructure of

Fig. 3. Nyquist plots for low-lime fly-ash systems at early stages[16].

interfacial transition zone (ITZ) between different aggregates and cement paste was also studied with this model [42].

2.3. Models for materials with supplementary cementitious materials or conductive materials McCarter et al. [16,17] reported that when a low-lime fly ash was introduced in cement pastes, prominent changes in electrical response of the system would be induced. As shown in Fig. 3, a plateau region exists between the electrode and the bulk arcs in the Nyquist plot of low-lime fly-ash systems at early hydration and the extent of the plateau region increases as the fly ash content increases. They attributed this to the enhancement in double layer polarization effects on the surface of fly ash particles and demonstrated it in later 2004 [24]. They also found that the extent of the distinctive plateau region in low-lime fly-ash cement paste was influenced by the unburnt carbon content in fly ash. At present, equivalent circuit models in this field are still limited and the elements in the circuit models lack clear physical meaning with respect to the microstructure or property of the sample. Cruz et al. [9] proposed an equivalent circuit model with CPE for portland cement mortar containing high percentage of pozzolans. The model was applied to describe the microstructure of the mortar at any age. The Q-factor and n-exponent of the CPE could be used to evaluate the electric conductivity of conductive materials or the dielectric constant of dielectric materials by using a binary mixture conductivity formula [43]. The constant phase angle index n of the mortar varied with types and contents of pozzolanic material. Thus, it can be used to reflect the percentage of dielectric materials at the solid–solution interface within the mortar. The characteristics of CPE in the equivalent circuit model can be used to distinguish different pozzolanic materials in the mortar. Woo et al. [8] put forward an equivalent circuit for cement paste with conductive materials, which required to input the conductivity of the matrix, the intrinsic conductivity and volume fraction of insulated particles or fibrous materials. One or two high frequency arc(s) would exist in Nyquist plots by changing the resistance of insulated particles or fibrous materials (Rp) as shown in Fig. 4. When fibrous conductive materials were added to the system, random distribution of fibers should be taken into consideration during the fitting process to diminish the disagreements between the model and measured spectrum. Meanwhile, it can reflect the uneven and unaligned distribution of fibers in forming process and provide useful information on microstructural changes due to loading and/or cycled fatigue by the deviations of electrochemical parameters.

Fig. 2. (a) Schematic representation and (b) simplified model of microstructure of concrete[7]. 4

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

results with different conductive loops or time constants [5,16,25,38]. A differential impedance analysis (DIA) method was mostly applied to identify the number of time constant in literature [25,48,49]. Recently, He et al. [50] proposed a modified DIA method considering the CPE behavior of cement-based materials, which was beneficial for establishing a reasonable equivalent circuit of impedance spectroscopy with a CPE behavior. The wider application of AC impedance spectroscopy technique in practice needs further study on the determination of electric circuit model. 3. Application of AC impedance spectroscopy measurements for cement-based materials 3.1. Application of AC impedance measurements in monitoring hydration process Fig. 4. Typical Nyquist plots for cement paste with different conductive materials[8].

At early ages, the researches on AC impedance spectroscopy were mainly focused on the characterization of cement hydration at early age [51–55]. In 1991, Scuderi et al. [38] found that one or two high frequency arc(s) were obtained during early hydration. The diameter of high frequency arc gradually increased with hydration due to a decrease of electrolyte content and pore connectivity and/or an increase in layering following sliding between C-S-H sheets [56,57]. Orazem et al. [58] studied the influences of combined relative humidity and temperature on the microstructure change of portland cement mortars with long hydration time by impedance spectroscopy. The experimental results were analyzed by the circuit model proposed by Cabeza et al. [25] and the variation of circuit parameters made it possible to analyze the evolution of the solid fraction within samples. Seong et al. [59] found that the diameter of high frequency arc of portland cement paste showed a decreasing trend during the first day of hydration. After that, it started to increase with setting time as shown in Fig. 5. They attributed this to the presence of a small amount of unreacted or intrinsically formed CaO, which may increase the ionic conductivity of liquid phase and slightly reduce the interconnectivity of ion-rich solution phase at early hydration age. Recently in 2017, the effects of substitution and particle size of volcanic ash on pozzolanic reaction and water dynamics during early age hydration up to 3 h by using AC impedance spectroscopy were studied and it was demonstrated as a powerful tool to study free and bound water transformation during hydration of cement pastes [60]. In 1992, Gu et al. [18] investigated the hydration mechanism of portland cement paste immersed in lime solution from 48 to 380 h by AC impedance spectroscopy. The obtained Nyquist plot and the simulated RC parameters (summarized in Table 2) showed that in the early hydration time the bulk resistance Rt(s+l) increased mainly due to the

2.4. Chloride migration models The penetrated chloride ions within cement-based materials can bring some changes to the composition of pore solution and solid-liquid interface. Meanwhile, the reaction of chloride ions with solid phase also affects the pore structure of the materials. Among several equivalent electrical circuits used in cement-based materials, Jain et al. [44] used a model accounts for the bulk arc in Nyquist plot to study the microstructural changes in concretes subjected to non-steady state chloride migration tests. The reaction kinetics and diffusion process can be characterized by Faradaic impedance, which is composed of a resistance of charge transfer in series with a diffusion behavior related Warburg impedance. Based on these, Shi et al. [45] proposed a new method to determine the diffusion coefficient of chloride ions in concrete with an electric circuit model also contain a Warburg impedance element. This model was also used by Dong et al. [46,47] to characterize the CO2 diffusion behavior of fly ash blended cement materials. Sánchez et al. [10] proposed a model to analyze the variations in microstructure of concrete during the electrical accelerated chloride migration test. The evolutions of the dielectric parameters showed that during the migration test, the concrete samples became saturated with chlorides firstly, then the formation of new solid phases resulted into the decrease of pore diameter. In their study, these interpretations were confirmed experimentally by mercury intrusion porosimetry results. With a correlation between pore resistance Rc and rapid chloride transport parameters, Neithalath et al. [26] developed a methodology to quantify the relative influences of pore solution conductivity and pore structure on the rapid chloride migration parameters. Based on the proposed circuit model and experimental results, the study showed that during the migration test, it was the reduction in pore connectivity but not the porosity that highly affected the rapid chloride transport parameters. Since 1990s, extensive studies on equivalent circuit model for AC impedance spectroscopy have been conducted, which built a foundation for wider applications of this technique in the next decades. An appropriate equivalent circuit model is very important to AC impedance spectrum analysis. However, the inhomogeneous and complex structure and complicated components result into the indeterminacy of an electric equivalent circuit for a typical cement-based material. For one set of data, several models may be well fitted better or less. The hydration of cement does have significant influences on the performance of samples, which may sometimes change the corresponding best fitted equivalent model. In all, for different systems, the key problem to propose an appropriate equivalent circuit model is to identify the number of time constants, namely the R/C networks in high-frequency region of impedance spectrum. The equivalent circuit models have been proposed in many researches to interpret the AC impedance

Fig. 5. Nyquist plots of portland cement in the early hydration time[49]. 5

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

Table 2 Variation in modelled and experimental by determined electrical parameters with increasing hydration time [18]. Hydration Times (hours)

Rt(s + l)(ohms)

Rt(int) (ohms)

Ct(int)(nF)

Ct(estimated)(nF)

Top Freq. (MHz)

48 68 169 194 286 380

80 87 99 104 111 113

– – 13.5 15.0 25.0 30.0

– – 7.2 5.0 3.2 3.0

– – 12.0 10.8 4.2 3.5

– – 0.978 0.978 1.506 1.506

significant decrease in free water content, while solid resistance contributed to the increase of Rt(s+l) at later stage. The evolution of high frequency arc diameter, interfacial resistance and solid-liquid interfacial capacitance were all highly dependent on the microstructural development and could be used to qualitatively characterize the hydration degree. Diaz et al. [61] studied the bulk resistance (Rb) of mortars saturated with 1.0 mol/L NaCl solution and found it gradually increased up to 28 days of curing, but afterwards it decreased until the end of the testing as shown in Fig. 6. They attributed this to the increased porosity in terms of OH− leaching before 28 d and the development of a totally different conductive path due to the formation of Friedel's salt in interlamellar spaces after that. In the study of Bruce et al. [62], it was investigated that the value of Rb increased with increasing silica fume content and/ or decreasing w/b ratio. While the value of pore solution conductivity increased rapidly at the early stage and then keep constant for paste without silica fume and decreased sharply for silica fume-blended cement paste. Based on the binding form of the cement paste with the water obtained from AC impedance spectroscopy, Zhang et al. [63] classified the hydration process of cement-based materials into primary, secondary and tertiary stages. McCarter et al. [64] monitored the long-term hydration characteristics of concretes with and without mineral supplementary cementitious materials by AC impedance technique. The normalized conductivity was introduced to study the hydration kinetics of cementitious materials at different hydration stages. This parameter is able to distinguish the hydration degree and pore-solution chemistry of different cementitious materials. From the schematic diagram of normalized conductivity versus time presented in Fig. 7, four stages or regions for concrete hydration can be distinguished: initial region (I), transition region (II), acceleration region (III) and deceleration region (IV). The results were consistent with the heat evolution curves of portland cement examined by a conduction calorimeter [65]. Based on a three-branch electric equivalent model, Cruz et al. [9] investigated the hydration degree of cement mortars by the AC impedance parameters and quantified the electrical properties of the hydration products located at the solid–liquid interface. Dotelli and Mari [66] studied the possibility of using AC impedance spectroscopy to follow the hydration process of cement paste by traditional techniques including Xray diffraction and thermogravimetry. The study showed a good agreement between results obtained from these different methods. Porosity is a very important parameter to characterize the microstructure and hydration process of cement-based materials. However, under some conditions connectivity and tortuosity of pores dominate the performance of materials. Conductivity represents the transmission capability of electricity within material, which can reflect not only the porosity, but also the pore connectivity and tortuosity of the material. The variation of conductivity of cement-based materials can be represented as follows:

tref n σt = σref ⎛ ⎞ ⎝ t ⎠

Fig. 6. Nyquist impedance plots for mortar sample saturated with NaCl 1 mol/L solution. (A) Evolution from day 0 to day 28 and (B) evolution from day 28 to the end of the experiment[61].

where, σt is the conductivity at time t, σref is the conductivity at reference time tref, n is hydration index. The value of σref for cement-based materials is generally increased with w/c ratio. The research on conductivity of cement-based materials by AC impedance spectroscopy is significant for the study of the hydration process and can provide useful information on evolution of microstructure with hydration. In a recent study [67], the drying profile inside the cement matrix was investigated by AC impedance spectroscopy during curing process with different external drying levels. According to the resistivity obtained from impedance analysis, moisture distribution and drying depth estimation of cementitious system were non-destructively studied. Ortega et al. [68] reported that the results of impedance spectroscopy measurement were more influences by the drying of materials than microstructure development and it would be not suitable for following the evolution of the pore structure under non-optimum conditions. James et al. [69] found that the interfacial phenomena associated with collapse of C-S-H structure during drying process resulted into presence of an

(2) 6

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

intermediate arc in the Nyquist plot. 3.2. Application of AC impedance spectroscopy in studying microstructure evolution As can be seen from the above sections, parameters in equivalent circuit models have close relationship with the microstructure of cement-based materials. Many equivalent circuit models were proposed with consideration on microstructural properties of testing materials, and some microstructure-based models were also used for studying other phenomenon such as ion migration and steel corrosion. Quantitative studies on microstructure of cement-based materials by AC impedance spectroscopy are mainly based on the relationship between the effective conductivity of samples σeff and the bulk resistance Rb from AC impedance spectroscopy (abscissa of the intersection of the bulk and electrode arcs in a Nyquist plot) [26,44] as:

σeff =

L Rb A

(3)

where L and A are the length and effective testing area of the sample. The obtained effective conductivity can be used to evaluate the diffusion properties of the samples, and also has close relationship with pore structure as follows [70]:

σeff = σpore (ϕβ )

(4)

where (ϕβ) is lumped pore structure parameter, which is the product of porosity (ϕ) and pore connector factor (β), σpore is pore solution conductivity. In the study of Neithalath and Jain [26], two conductivity ratios were defined as follows: ∗ σeff =

(σeff )modified − concrete (σeff ) plain − concrete

∗ σpore =

(5a)

(σpore )modified − concrete (σpore ) plain − concrete

(5b)

Based on these two equations, the changes of overall effective conductivity and pore solution conductivity of samples after modified by silica fume and fly ash were studied. Dividing Eq. (5b) by Eq. (5a), then substituting Eq. (4) gives: ∗ σpore ∗ σeff

=

(ϕβ ) plain − concrete (ϕβ )modified − concrete

= (ϕβ )∗ (6)

The value of (ϕβ)* can be used to evaluate the pore structure refinement due to the cement replacement by additions. The samples with fly ash at later age and silica fume at all age showed (ϕβ)* values higher than 1.0, which indicated pore structure refinement for the modified concrete. However, the microstructural improvement for concrete with fly ash maybe not occurred at early hydration age due to the low pozzolanic reactivity of fly ash. Another studies [44,71] also used this method to follow the change of microstructural parameter (ϕβ) by adding vitreous calcium alumino-silicate and glass powders. Idealizing all the connected pores of a sample into one single pore with entire features retained, a simplified equivalent connected pore diameter (dconn) was calculated according to the resistance of connected pores [26]. As shown in Fig. 8, it can be seen that the pore structure refinement effects of silica fume are much higher than those of fly ash compared to plain concrete. Based on the pore fractal theory, Tang et al. [72] developed a non-contact impedance measurement to test porosity and pore volume fraction and the results were compared to MIP test. Cabeza et al. [73] studied the influences of applied load on electric properties of cement pastes and found that R2 and C2, which were resistance and capacitance relate to the pore solution, had totally different relationships with the applied load as shown in Fig. 9. They attributed this to the occurrence of creep within samples when interlayer

Fig. 7. Temporal changes in conductivity (a) and normalized conductivity (b) values. (at 75 mm) over test period for concrete mixes and (c) schematic diagram of the four stages shown in (a) and (b)[64].

7

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

issues such as clumping/aggregation in nanocomposites. Ozyurt et al. [86–88] studied the fiber dispersion in fiber-reinforced cementitious materials by AC impedance spectroscopy and compared the results were verified by image analysis. Hong et al. [89] studied the bond degradation between external carbon FRP reinforcement and concrete, the capacitance parameters from equivalent circuit model strongly correlated with the interfacial crack length between the carbon FRP and concrete. It was quantitatively shown that the electric conductivity of hardened cement paste depended on the pore surface area at low relative humidity while dominated by the pore volume at high relative humidity [90]. Ortega et al. [91,92] studied the effects of environmental conditions in the microstructural development of ordinary potland and slag cement mortars by AC impedance spectroscopy, and mercury intrusion porosimetry as a contrast technique. The results showed that ordinary portland cement pastes were more influenced by relative humidity while temperature affected slag cement mortars greater. Perron and Beaudoin et al. [93] found that impedance spectrum was influenced by freezing and flowability of pore solution within testing sample. Sato et al. [30,94,95] established the relationship between microstructure of fiber reinforced cement pastes and elements in equivalent circuit model during freezing-thawing cycles. When subjected to freezing condition, resistance of liquid phase in pore reached its minimum at the temperature of −40 °C due to the leaching of Na+, K+, OH− and Cl− and the freezing of water within capillary and gel pore. In this process, the solid-liquid interfaces (C-S-H gels and liquid water) gradually transformed into the solid-solid interfaces (C-S-H gels and ice) as shown in Fig. 10. The homogeneity should be the same before and after freezing-thawing cycle, while the decrease of roughness due to the freezing of liquid in capillary and gel pores significantly increased the constant phase angle index. The ratio of freezing ice resistance to the liquid water resistance provided useful information for calculation of the amount of freezable water and assessment of the durability of cement paste. In their studies, the variation of microstructure due to the volume increase of pore solution during freezing process was ignored. The results of Zhong et al. [96] showed that the impedance characteristics of polymer-modified mortars were related to close contact, the packing, and the formation of a mechanically rigid film of the polymer particles.

Fig. 8. Predicted idealized equivalent pore diameters from the circuit model [26].

Fig. 9. Dependence of circuit elements on applied load[60].

water moved away towards the unoccupied spaces (pores) due to the external load. The moving water would dissolve ions from pore walls and increase the total amount of electrolyte in pores. Thus, the bulk resistance R2 decreased while C2 increased. With the increase of bending stress applied to the specimens, the total equivalent resistance gradually decreased, which showed the increase of defects in samples. For same bending stress level, the ratio of bending stress to flexural strength showed obvious influences on total resistance [74]. According to the microstructure evaluation, AC impedance spectroscopy is also applied in studying the mechanical properties of cementitious materials, such as compressive strength [75,76], tensile strength [77], fracture toughness [78], microcracking [79,80] and other types of loading [81]. Especially when steel fiber or fiber reinforced plastic (FRP) are introduced, the enhanced pore structure and restrain of crack developing under external loading can be easily detected by AC impedance spectroscopy. Torrents et al. [82,83] studied the differences in impedance responses of cement-based composites with and without fibers. Generally, an extra arc can be observed for fiber-reinforced samples. They explained this with the thin, resistive, and highly capacitive layers formed on the surfaces of the conducting fibers, which was confirmed later with a “frequency-switchable fiber coating” model [84]. Wansom et al. [85] investigated the impedance response of fiber-reinforced cement composites with multi-walled carbon nanotubes, the results indicated that AC impedance spectroscopy was able to discriminate the contribution of percolation from discontinuous nanotubes and potentially characterize the dispersion

3.3. Application of AC impedance spectroscopy in determining ion migration parameters A variety of techniques have been used in determining the chloride penetration parameters of cement-based materials [97,98]. However, there are lots of limitations for the application of these methods due to the long testing time and/or microstructural variation during the testing periods. The development of AC impedance spectroscopy measurement makes it possible to continuously follow the chloride transportation process and microstructural change during chloride diffusion and electric migration tests. Liu and Beaudoin [99,100] investigated the aspect of the rapid chloride permeability test by AC impedance technique. The results observed linear relationships between the bulk resistance Rp, passed charge, and initial current. It was concluded that AC impedance test result was an equivalent indication of the relative permeability and the total passed charge. In the study of Aït-Mokhtar et a [101], the bulk resistances of reinforced cement mortars with different w/b ratios, coating thicknesses and porosity were studies and the correlation to chloride diffusion coefficient was obtained. By using the low-frequency region in the impedance spectrum, Shi et al. [45] calculated the chloride migration coefficient and found a decreasing trend during curing period. However, their study did not distinguish the migration of chloride ions from other ion species. The results obtained by this method were more close to migration coefficient of all the aggressive ions. Based on the Einstein-Smoluchowski equation [102] and the assumption that the conductivity contribution 8

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

them. With an experimental protocol based on a four-electrode arrangement, Loche et al. [109] studied the influences of chloride ion migration on the electrochemical impedance spectroscopy of cement mortar. The results showed that the penetrated chloride ions modified impedance response of samples and a small loop at low frequency range of the Nyquist plot due to interface phenomena at the paste-solution interface was revealed. Also by means of this technique, the chloride transport behavior of fly ash blended cement material was investigated in a recent study [110] and the relationship among resistance of ion transfer process, penetration time and penetration depth within fly ash-blended cement paste was deduced. Lizarazo-Marriaga et al. [111] studied the electrochemical impedance properties of Portland cement mortar in high-frequency region (104 to 3*105 Hz) and studied the relationship between ITZ properties and the electrical elements defined in the equivalent circuit adapted from Song [7] and their effects on rapid chloride penetrability (RCP) test results. It was found that the passed charge during RCP test was mainly controlled by the conductive pores. In some studies [112–114] on ion diffusion in ionic electrolyte solution and metal electrode, the capacitance of electric double layer (EDL) has been widely applied. Due to the complexity and inhomogeneous of cement-based materials, the application of AC impedance spectroscopy in studying the interfacial properties and ion exchange and migration at the solid-liquid interface of cement-based materials is limited. In a recent study [115], the properties of EDL formed at the solid-liquid interface of cement paste were investigated by AC impedance. With a determined equivalent circuit model with EDL capacitor, the EDL capacitance of cement pastes immersed in NaCl solution was obtained and transferred into normalized thickness of EDL. The results showed that the thickness of EDL was decreased with the increase of ion concentration in pore solution, which was in agreement with the Debye formula. With a proposed equivalent circuit model containing ion diffusion resistor at cement paste solid/liquid interface, it was also found that the addition of fly ash improved ion transfer resistance at the solid-liquid phase interface [110]. 3.4. Application of AC impedance spectroscopy in evaluating steel corrosion When exposed to a chloride environment, a steel reinforced concrete structure may simultaneously experience plenty of chemical, physical and electrochemical actions. However, the corrosion of steel is mainly related to electrochemical actions. The AC impedance spectroscopy can reveal different reaction steps and corrosion rate, which may dominate at certain frequencies. From the aspects of steel, the processes of passive layer formation and growth and pitting corrosion have been extensively studied by AC impedance spectroscopy with low frequency range [116,117]. Dong et al. [118] studied the effects of a novel selfhealing microcapsule on steel corrosion inhabitation of steel in the simulated concrete system of saturated Ca(OH)2 solution with specific pH value. However, the inhomogeneous composition and complex structure of cement-based materials make it more difficult for determination of equivalent circuit model analysis of impedance results from reinforcing steel concrete [119]. Berrocal et al. [120,121] studied the influences of fiber dosage and fiber geometry on matrix resistance Rb of cementitious materials containing steel fibers. In their study, the matrix resistance and resistivity were tested and compared to DC measurement results. The results showed that the addition of steel fibers did not significantly affect the DC and AC matrix resistivity of the mortar prisms. Feiliu et al. [122,123] studied the impedance behavior of steelconcrete interface and examined the most suitable equivalent circuit for modelling the system during chloride-related corrosion. Ford and Mason [124] reported that three arcs could be obtained in the impedance spectrum of cement paste/reinforcing steel systems, in which the high frequency bulk (MHz) represented diffusivity and permeability of the paste, the medium frequency arc (Hz) provided insight into the porosity of the near interfacial zone of the paste/steel system, and the

Fig. 10. (up): Illustration of the “C-S-H gel interface” of capillary pores (below): the depression angle parameter versus temperature for a cement paste specimen subjected to the freeze-thaw cycle[30].

of the intrinsic ions in pore solution can be neglected, Diaz et al. [103] also proposed a method to calculate the chloride diffusion coefficient according to the resistance of percolating pores R1. In 2012, Mercado et al. [104] proposed a method to calculate the diffusion coefficient of a typical ionic species from the resistance of saturated material. The Nernst-Einstein Equation and formation factor were used in this method. This approach would be questionable for other materials, but was proven to be valid for cement-based materials by some researchers [105,106]. The chloride diffusion coefficients measured by this method were in agreement with those obtained by migration test and current measurement. Recently, Wu et al. [107] summarized test procedure for determining the chloride ion diffusion coefficient based on AC impedance spectroscopy. Correction factors for different cementitious materials were proposed to eliminate the influence of other ions on testing results. Akhavan and Rajabipour [108] quantified the effects of cracks on ion diffusivity of cement paste by AC impedance spectroscopy measurement, the results showed that the diffusion coefficient of cracked sample was significantly influenced by the crack volume fraction and there was linear correlation between 9

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

low frequency arc (mHz) related to the passive nature of the steel. Generally, it is necessary to detect the corrosion at early stage to ensure the safety of the concrete structure and schedule the repairing work. Rapid and accurate methods for corrosion rate measurement are of tremendous importance for practical applications. Many studies [125,126] for evaluation of the corrosion rate of a metal or steel have been conducted based on electrochemical method and Faraday's law. The relationship between corrosion rate (CR) of steel and the density of corrosion current icorr can be derived from Faraday's law [39]:

CR (μm / y ) =

3.27 × icorr × E . W . d

(7)

where E.W. represents the equivalent mass of steel (gm) and d is the density of reinforcing bar (gm/cm3). Nowadays, the corrosion rate of reinforcing steel embedded in concrete was calculated by results of AC impedance spectroscopy via Stern-Geary equation [127]:

icorr = B / Rp being B =

ba bc 2.303(ba + bc )

(8)

where B is the Stern-Geary constant, ba and bc are the Tafel slopes for the anodic and cathodic reactions, respectively. The resistance of the steel-solid surface and the corrosion products Rp can be obtained from AC impedance measurement. By using this method, Wei et al. [128] studied the corrosion evolution of reinforcing steel in concrete under dry/wet cyclic and four stages controlled by different mechanisms including passive stage, local corrosion, accelerated corrosion, and constant rate corrosion were observed. The Stern-Geary equation is also applied in some other techniques to monitor corrosion rate of reinforced concrete, such as polarization measurements [129]. Ismail et al. [39] studied the corrosion rate of reinforcing steel in conventional portland cement concrete and high performance concrete (HPC). The results demonstrated a reasonable agreement among the results of AC impedance, Tafel plot and linear polarization resistance (LPR). Meanwhile, lower corrosion rate was obtained for HPC specimen compared to that in conventional cement concrete. Pradhan and Bhattachariee [130] conducted similar research and correlated icorr measured by these measurements, as shown in Fig. 11, and could be expressed as follow:

icorr (LTR) = 1.10 × icorr (AC impedance ) = 0.99 × icorr (gravimetric )

Fig. 11. Variation of Icorr between (a) LPR and AC impedance, (b) LPR and gravimetric[107].

(9)

In some studies, other techniques such as visual examination [131] and corrosion potential measurement [132] were also conducted to assess the validity of AC impedance spectroscopy in estimating the corrosion rate of reinforced concrete. Qiao and Ou [133] studied the pitting corrosion process of reinforcing steel in cement mortar by AC impedance spectroscopy and the results were compared to and explained by electrochemical noise analysis test. The results showed that corrosion process of steel in cement mortar was controlled by the diffusion of oxygen shown in low frequency region of Nyquist plot. The rough surface of cement mortar and pitting corrosion were characterized by the deviation degree of Nyquist plot from straight line with slope of 1 in low frequency region. Dhouibi et al. [134] used AC impedance spectroscopy to determine the long-term effectiveness of corrosion inhibitor for steel in concrete. In their studies, information on changes of surface film and charge transfer on the steel surface was investigated by variations of resistance and capacitance related to different frequency arcs in Nyquist plot. However, for steel corrosion evaluation, a lower frequency (< 10−3 Hz) is needed in future study to obtain an apparent capacitive arc relates to steel corrosion process. As a non-destructive technique, AC impedance spectroscopy has received more and more concerns in detecting microstructural evolution and quality evaluation of existing structure. With the development of testing technology and analytical tool (eg. equivalent circuit model), this technique has been applied in a wider range of field. According to the studies of Dong et al. [135,136], the electrochemical impedance parameters was able to applied to determine the carbonation behavior of cement materials and an empirical formula was proposed to describe

the relationship between carbonation depth and electrochemical parameters. The effectiveness of AC impedance spectroscopy on characterization of sulfate diffusion process is also confirmed in literature [137]. In 2013, Wansom and Janjaturaphan [31] explored and indicated that AC impedance spectroscopy can potentially serve as a reliable and convenient tool to electrically evaluate fiber orientation in fiber-cements. As an electrochemical testing measurement, AC impedance can also provide information about properties of interfacial between different phases, which is considered as a key feature governing the properties of concrete. In the study of Kong et al. [138], resistance of connected pore obtained from AC impedance measurement was used as the electrical property that characterizes the microstructure of ITZ between aggregate-cement pastes. The results obtained in this study proved that AC impedance spectroscopy can also be a powerful tool for evaluation of the microstructure of the ITZ. Nowadays, the application of AC impedance spectroscopy is more being concentrated in the characterization of physical or mechanical properties of cement-based materials. In the next decades, the application of AC impedance spectroscopy may more focus on interfacial properties determination and on-site detection. 4. Experimental conditions control and data analysis The 2-point or 4-point measurements are usually used to investigate the impedance spectrum of cement-based materials. However, the existence of capacitance between the contact surface of the specimen and 10

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

error of stray impedance correction with capacitors of known capacitance. It was found a resistor of higher resistance or capacitor of lower capacitance than testing cement sample was required to lower the error of stray impedance correction, which was difficult to achieve due to unknown resistance and capacitance of cement-based materials before testing. Based on the studies of different configurations for open and short circuit tests and comparison with actual situation, a method for stray impedance correction was proposed and acceptable correction error was obtained with this method [147,151]. Also, the precise control of laboratory temperature and noise, the reducing alternating current amplitude and the shorter testing time are all important for the measurement and analysis [150].

potential sensor could strongly influence the result of 4-point measurement. Thus, it is difficult for 4-point measurement to accurately detect electrochemical characteristics of the sample due to the expansion of low frequency arc and/or overlap between low and high frequency arcs [11]. Actually, the value of contact capacitance in 4-point measurement was generally much larger than that of the capacitance of specimen obtained from 2-point measurement, and was undetectable in high frequency range. Thus, the 2-point measurement shows advantages in revealing the electrochemical properties of cement-based materials. The effects of cement paste/electrode interface on high frequency arc are still controversy and need further study. He et al. [139] studied the effects of electrode/sample impedance on impedance spectroscopy measurement results of cement paste when using different electrodesample contact methods. The results showed indicated that conductive glue and electrode pre-casting contact are reasonable for impedance measurement than demolded sample-electrode contact, while the electrode pre-casting was not recommended for samples cured in a drying environment. In some previous studies, higher values of dielectric constant were obtained in contact method [2] and were processed using Dielectric Amplification Factor (DAF) [3,4]. Keddam et al. [5] placed mylar films between specimen and electrode and a larger dielectric constant was obtained in comparison to normal ceramics materials. A dielectric constant about 70–80, which is close to real dielectric constant of portland cement, was obtained in non-contact method with an air gap of 100 μm at each side of the samples [15]. However, the impedance spectroscopy results obtained from non-contact method cannot be well defined in Nyquist plot due to the pure capacitive behavior in high frequency regions [140]. In previous studies [39,130], contact method with stainless steel electrode settled in during the molding process was commonly applied and specimens were kept molded during the testing. This method can eliminate the problems induced by electrode/specimen interface. With this method, it was found that the high frequency arc in impedance spectrum shows close relationship with the microstructure characteristics of cement-based materials, such as the solid phase fraction [5,15], the migration of free ions in electrolyte filling pores, interlayer space in C-S-H, continuous capillary and air voids [141], critical value of pore diameter and micro-pores volume [142,143]. McCarter [33] found that before the setting of cement paste or mortar, the development of high frequency arc was slow. After that, the formation of tortuous capillary pore network in any direction accelerated the development of high frequency arc. However, obvious high frequency arc could also be detected prior to the setting of concrete, which strongly related to the volume fraction of aggregates within the system [45]. In a Nyquist plot, the high frequency resistance (R1), the depression angle (α) and the bulk resistance (Rb) all relate to the microstructure of cement-based materials and can be qualitatively analyzed. While, Ford et al. [144] found that when contact method was applied, the drying/shrinkage of imperfect electrodes could generate an extra arc in the obtained Nyquist plot of cement paste. During the AC impedance measurement, the stray impedance including stray resistance, capacitance and inductance can be produced due to the electrode and wire connected to electrode and testing equipment, especially at high frequency range [145,146]. Under some conditions, the effects of stray impedance of electrode and wire on testing result of AC impedance can be up to as high as 60% [147]. In 1994, Christensen et al. [2] proposed a method to eliminate the effects of stray impedance on measurement results of AC impedance. In this method, the open and short circuit impedances were tested and applied to represent the stray parallel and series impedance. This method has been applied in many subsequent studies. However, it was found that the impedance measured by open circuit was different from real condition when the sample was placed in a measuring cell [148,149]. An electrical component with known impedance was suggested to be used for stray impedance correction. However, He et al. [147] evaluated the

5. Conclusions This paper has reviewed the application of AC impedance spectroscopy in characterization of cement-based materials and the following conclusions were made based on discussions: 1. The equivalent circuit models proposed in literature based on simulation approaches, microstructure consideration, supplementary cementitious or conductive materials and chloride migration related are overviewed. Generally, the potential conductive path and microstructure of testing samples are two important factors considered for determination of equivalent circuit model. 2. With some mathematical and physical models, the electrical parameters obtained in AC impedance spectroscopy can be applied to characterize hydration properties, microstructural evolution, ion migration and steel corrosion process of cement-based materials. 3. The application of AC impedance spectroscopy in cement-based materials focuses more in physical or mechanical properties characterization, which may change into interfacial properties and onsite detections in the next decades. 4. The control of testing conditions and use of appropriate testing method are very important to the application of AC impedance techniques. The effects of stray impedance due to electrodes and wires on testing results of AC impedance measurement have to be properly eliminated. Acknowledgements The financial help of the National Science Foundation of China (Project No., 51378196 and U1305243) are gratefully acknowledged. References [1] W. McCarter, S. Garvin, N. Bouzid, Impedance measurements on cement paste, J. Mater. Sci. Lett. 7 (10) (1988) 1056–1057. [2] B.J. Christensen, T. Coverdale, R.A. Olson, S.J. Ford, E.J. Garboczi, H.M. Jennings, et al., Impedance spectroscopy of hydrating cement‐based materials: measurement, Interpretation, and application, J. Am. Ceram. Soc. 77 (11) (1994) 2789–2804. [3] R. Coverdale, B. Christensen, T. Mason, H. Jennings, E. Garboczi, Interpretation of the impedance spectroscopy of cement paste via computer modelling, J. Mater. Sci. 29 (19) (1994) 4984–4992. [4] R. Coverdale, H. Jennings, E. Garboczi, An improved model for simulating impedance spectroscopy, Comput. Mater. Sci. 3 (4) (1995) 465–474. [5] M. Keddam, H. Takenouti, X. Novoa, C. Andrade, C. Alonso, Impedance measurements on cement paste, Cement Concr. Res. 27 (8) (1997) 1191–1201. [6] D.E. Macphee, D.C. Sinclair, S.L. Cormack, Development of an equivalent circuit model for cement pastes from microstructural considerations, J. Am. Ceram. Soc. 80 (11) (1997) 2876–2884. [7] G. Song, Equivalent circuit model for AC electrochemical impedance spectroscopy of concrete, Cement Concr. Res. 30 (11) (2000) 1723–1730. [8] L. Woo, S. Wansom, A. Hixson, M. Campo, T. Mason, A universal equivalent circuit model for the impedance response of composites, J. Mater. Sci. 38 (10) (2003) 2265–2270. [9] J. Cruz, I. Fita, L. Soriano, J. Payá, M. Borrachero, The use of electrical impedance spectroscopy for monitoring the hydration products of Portland cement mortars with high percentage of pozzolans, Cement Concr. Res. 50 (2013) 51–61. [10] I. Sánchez, X. Nóvoa, G. De Vera, M. Climent, Microstructural modifications in

11

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

[11]

[12] [13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24] [25]

[26]

[27]

[28] [29] [30]

[31]

[32] [33] [34] [35]

[36]

[37]

[38] [39]

[40]

[41]

[42] L. Kong, L. Hou, X. Bao, Application of AC impedance technique in study of lightweight aggregate-paste interface, Constr. Build. Mater. 82 (2015) 332–340. [43] T. Zakri, J.-P. Laurent, M. Vauclin, Theoretical evidence forLichtenecker's mixture formulae'based on the effective medium theory, J. Phys. D Appl. Phys. 31 (13) (1998) 1589. [44] J. Jain, N. Neithalath, Electrical impedance analysis based quantification of microstructural changes in concretes due to non-steady state chloride migration, Mater. Chem. Phys. 129 (1–2) (2011) 569–579. [45] M. Shi, Z. Chen, J. Sun, Determination of chloride diffusivity in concrete by AC impedance spectroscopy, Cement Concr. Res. 29 (7) (1999) 1111–1115. [46] B. Dong, Q. Qiu, Z. Gu, J. Xiang, C. Huang, Y. Fang, et al., Characterization of carbonation behavior of fly ash blended cement materials by the electrochemical impedance spectroscopy method, Cement Concr. Compos. 65 (2016) 118–127. [47] B. Dong, Q. Qiu, J. Xiang, C. Huang, F. Xing, N. Han, Study on the carbonation behavior of cement mortar by electrochemical impedance spectroscopy, Materials 7 (1) (2014) 218–231. [48] D. Vladikova, Z. Stoynov, L. Ilkov, Differential impedance analysis on single crystal and polycrystalline Yttrium iron garnets, Pol. J. Chem. 71 (8) (1997) 1196–1203. [49] D. Vladikova, J. Kilner, S. Skinner, G. Raikova, Z. Stoynov, Differential impedance analysis of single crystal and polycrystalline yttria stabilized zirconia, Electrochim. Acta 51 (8–9) (2006) 1611–1621. [50] F. He, R. Wang, C. Shi, R. Zhang, C. Chen, L. Lin, et al., Differential analysis of AC impedance spectroscopy of cement-based materials considering CPE behavior, Constr. Build. Mater. 143 (2017) 179–188. [51] M. Shi, Y. Zhang, Study of cement hydration in the early and middle periods by AC impedance technique (I)-AC impedance response in initial period, J. Build. Mater. 5 (2002) 210–214. [52] C. Liu, Y. Huang, H. Zheng, Study of the hydration process of calcium phosphate cement by AC impedance spectroscopy, J. Am. Ceram. Soc. 82 (4) (1999) 1052–1057. [53] S.-M. Kim, J.-H. Hwang, Application of impedance spectroscopy to cement-based materials: hydration of calcium phosphate bone cements, J. Korean Chem. Soc. 43 (3) (2006) 156–161. [54] H. Romeo, P. Bueno, M. Fanovich, Application of impedance spectroscopy to evaluate the effect of different setting accelerators on the developed microstructures of calcium phosphate cements, J. Mater. Sci. Mater. Med. 20 (8) (2009) 1619–1627. [55] X.P. Xian, Y.S. Wang, F. Xing, B.Q. Dong, Measuring and modeling analysis of electrochemical impedance spectroscopy for hydration procedure of cement materials, Adv. Mater. Res.: Trans. Tech. Publ. (2012) 1033–1036. [56] J.-H. Hwang, Impedance spectroscopy analysis of hydration in ordinary Portland cements involving chemical mechanical planarization slurry, J. Korean Chem. Soc. 49 (3) (2012) 260–265. [57] B. Tamtsia, J. Beaudoin, J. Marchand, The early-age short-term creep of hardening cement paste: AC impedance modeling, J. Mater. Sci. 38 (10) (2003) 2247–2257. [58] M.E. Orazem, B. Tribollet, Electrochemical Impedance Spectroscopy, John Wiley & Sons, 2011. [59] K.-P. Seong, S.-Y. Jeon, B. Singh, J.-H. Hwang, S.-J. Song, Comparative study of an experimental Portland cement and ProRoot MTA by electrochemical impedance spectroscopy, Ceram. Int. 40 (1) (2014) 1741–1746. [60] A. Husain, K. Kupwade-Patil, A.F. Al-Aibani, M.F. Abdulsalam, In situ electrochemical impedance characterization of cement paste with volcanic ash to examine early stage of hydration, Constr. Build. Mater. 133 (2017) 107–117. [61] B. Díaz, L. Freire, P. Merino, X. Novoa, M. Pérez, Impedance spectroscopy study of saturated mortar samples, Electrochim. Acta 53 (25) (2008) 7549–7555. [62] B.J. Christensen, T.O. Mason, H.M. Jennings, Influence of silica fume on the early hydration of Portland cements using impedance spectroscopy, J. Am. Ceram. Soc. 75 (4) (1992) 939–945. [63] Y. ZHANG, M. Shi, Study of the hydration process of cement-based materials by AC impedance technique [J], J. Build. Mater. 2 (2000) 005. [64] W. McCarter, T. Chrisp, G. Starrs, A. Adamson, P. Basheer, S. Nanukuttan, et al., Characterization of physio-chemical processes and hydration kinetics in concretes containing supplementary cementitious materials using electrical property measurements, Cement Concr. Res. 50 (2013) 26–33. [65] C. Shi, R.L. Day, A calorimetric study of early hydration of alkali-slag cements, Cement Concr. Res. 25 (6) (1995) 1333–1346. [66] G. Dotelli, C. Mari, The evolution of cement paste hydration process by impedance spectroscopy, Mater. Sci. Eng., A 303 (1–2) (2001) 54–59. [67] H. Sun, Z. Ren, S.A. Memon, D. Zhao, X. Zhang, D. Li, et al., Investigating drying behavior of cement mortar through electrochemical impedance spectroscopy analysis, Constr. Build. Mater. 135 (2017) 361–368. [68] J.M. Ortega, I. Sánchez, M.Á. Climent, Impedance spectroscopy study of the effect of environmental conditions on the microstructure development of sustainable fly ash cement mortars, Materials 10 (10) (2017) 1130. [69] J.J. Beaudoin, B.T. Tamtsia, Effect of drying methods on microstructural changes in hardened cement paste: an AC impedance spectroscopy evaluation, J. Adv. Concr. Technol. 2 (1) (2004) 113–120. [70] N. Neithalath, J. Weiss, J. Olek, Characterizing enhanced porosity concrete using electrical impedance to predict acoustic and hydraulic performance, Cement Concr. Res. 36 (11) (2006) 2074–2085. [71] N. Schwarz, M. DuBois, N. Neithalath, Electrical conductivity based characterization of plain and coarse glass powder modified cement pastes, Cement Concr. Compos. 29 (9) (2007) 656–666. [72] S.W. Tang, Z. Li, E. Chen, H.Y. Shao, Impedance measurement to characterize the pore structure in Portland cement paste, Constr. Build. Mater. 51 (2014) 106–112.

Portland cement concrete due to forced ionic migration tests. Study by impedance spectroscopy, Cement Concr. Res. 38 (7) (2008) 1015–1025. P. Xie, P. Gu, J. Beaudoin, Contact capacitance effect in measurement of ac impedance spectra for hydrating cement systems, J. Mater. Sci. 31 (1) (1996) 144–149. D. Macphee, S. Cormack, D. Sinclair, AC impedance spectroscopy of pore reduced cements: influence of contact resistance, J. Mater. Sci. 35 (19) (2000) 4823–4826. D. Ravikumar, N. Neithalath, An electrical impedance investigation into the chloride ion transport resistance of alkali silicate powder activated slag concretes, Cement Concr. Compos. 44 (2013) 58–68. Y. Zhu, H. Zhang, Z. Zhang, Y. Yao, Electrochemical impedance spectroscopy (EIS) of hydration process and drying shrinkage for cement paste with W/C of 0.25 affected by high range water reducer, Constr. Build. Mater. 131 (2017) 536–541. C. Andrade, V. Blanco, A. Collazo, M. Keddam, X. Novoa, H. Takenouti, Cement paste hardening process studied by impedance spectroscopy, Electrochim. Acta 44 (24) (1999) 4313–4318. W. McCarter, G. Starrs, T. Chrisp, Immittance spectra for Portland cement/fly ashbased binders during early hydration1, Cement Concr. Res. 29 (3) (1999) 377–387. W. McCarter, T. Chrisp, G. Starrs, J. Blewett, Characterization and monitoring of cement-based systems using intrinsic electrical property measurements, Cement Concr. Res. 33 (2) (2003) 197–206. P. Gu, P. Xie, J.J. Beaudoin, R. Brousseau, AC impedance spectroscopy (I): a new equivalent circuit model for hydrated portland cement paste, Cement Concr. Res. 22 (5) (1992) 833–840. P. Gu, Z. Xu, P. Xie, J. Beaudoin, Application of AC impedance techniques in studies of porous cementitious materials:(I): influence of solid phase and pore solution on high frequency resistance, Cement Concr. Res. 23 (3) (1993) 531–540. P. Xie, P. Gu, Z. Xu, J. Beaudoin, A rationalized AC impedence model for microstructural characterization of hydrating cement systems, Cement Concr. Res. 23 (2) (1993) 359–367. Z. Xu, P. Gu, P. Xie, J. Beaudoin, Application of AC impedance techniques in studies of porous cementitious materials:(II): Relationship between ACIS Behavior and the Porous Microstructure, Cement Concr. Res. 23 (4) (1993) 853–862. Z. Xu, P. Gu, P. Xie, J. Beaudoin, Application of AC impedance techniques in studies of porous cementitious materials (III): ACIS behavior of very low porosity cementitious systems, Cement Concr. Res. 23 (5) (1993) 1007–1015. G. Xu, J. Beaudoin, C. Jolicoeur, M. Page, Microstructural InvestigationI of portland cement mortars containing varying dosages polynaphthalene sulfonate superplasticizer, Spec. Publ. 186 (1999) 253–274. W. McCarter, G. Starrs, T. Chrisp, The complex impedance response of fly-ash cements revisited, Cement Concr. Res. 34 (10) (2004) 1837–1843. M. Cabeza, P. Merino, A. Miranda, X. Nóvoa, I. Sanchez, Impedance spectroscopy study of hardened Portland cement paste, Cement Concr. Res. 32 (6) (2002) 881–891. N. Neithalath, J. Jain, Relating rapid chloride transport parameters of concretes to microstructural features extracted from electrical impedance, Cement Concr. Res. 40 (7) (2010) 1041–1051. P. Gu, P. Xie, Y. Fu, J. Beaudoin, AC impedance phenomena in hydrating cement systems: frequency dispersion angle and pore size distribution, Cement Concr. Res. 24 (1) (1994) 86–88. S.M.L.J.W. Keru, AC impedance method to study the mechanism of corrosion of rebar in concrete [J], J. Build. Mater. 3 (1998). W.J. McCarter, Effects of temperature on conduction and polarization in Portland cement mortar, J. Am. Ceram. Soc. 78 (2) (1995) 411–415. T. Sato, An AC Impedance Spectroscopy Study of the Freezing-Thawing Durability of Wollastonite Micro-fibre Reinforced Cement Paste, University of Ottawa, Canada, 2002. S. Wansom, S. Janjaturaphan, Evaluation of fiber orientation in plant fiber-cement composites using AC-impedance spectroscopy, Cement Concr. Res. 45 (2013) 37–44. X. AN, C. SHI, F. HE, D. WANG, AC impedance characteristics of ternary cementitious materials, J. Chin. Ceram. Soc. 40 (7) (2012) 1059–1066. W. McCarter, The ac impedance response of concrete during early hydration, J. Mater. Sci. 31 (23) (1996) 6285–6292. S. Ford, J.-H. Hwang, J. Shane, R. Olson, G. Moss, H. Jennings, et al., Dielectric amplification in cement pastes, Adv. Cem. Base Mater. 5 (2) (1997) 41–48. W. McCarter, A parametric study of the impedance characteristics of cement-aggregate systems during early hydration, Cement Concr. Res. 24 (6) (1994) 1097–1110. R. Duarte, A. Castela, R. Neves, L. Freire, M. Montemor, Corrosion behavior of stainless steel rebars embedded in concrete: an electrochemical impedance spectroscopy study, Electrochim. Acta 124 (2014) 218–224. O. Poupard, A. Aıt-Mokhtar, P. Dumargue, Corrosion by chlorides in reinforced concrete: determination of chloride concentration threshold by impedance spectroscopy, Cement Concr. Res. 34 (6) (2004) 991–1000. C. Scuderi, T. Mason, H. Jennings, Impedance spectra of hydrating cement pastes, J. Mater. Sci. 26 (2) (1991) 349–353. M. Ismail, M. Ohtsu, Corrosion rate of ordinary and high-performance concrete subjected to chloride attack by AC impedance spectroscopy, Constr. Build. Mater. 20 (7) (2006) 458–469. D. Ribeiro, J. Abrantes, Application of electrochemical impedance spectroscopy (EIS) to monitor the corrosion of reinforced concrete: a new approach, Constr. Build. Mater. 111 (2016) 98–104. D.E. MacPhee, D. Sinclair, S. Stubbs, Electrical characterization of pore reduced cement by impedance spectroscopy, J. Mater. Sci. Lett. 15 (18) (1996) 1566–1568.

12

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

34 (1) (2012) 68–75. [105] K.A. Snyder, C. Ferraris, N. Martys, E.J. Garboczi, Using impedance spectroscopy to assess the viability of the rapid chloride test for determining concrete conductivity, J. Res. Natl. Inst. Stand. Technol. 105 (4) (2000) 497. [106] K.A. Snyder, The Relationship between the Formation Factor and the Diffusion Coefficient of Porous Materials Saturated with Concentrated Electrolytes: Theoretical and Experimental Considerations, (2000). [107] L. Wu, P. Dai, Y. Li, Determination of the transport properties of structural concrete using AC impedance spectroscopy techniques, J. Eng. 2016 (2016). [108] A. Akhavan, F. Rajabipour, Evaluating ion diffusivity of cracked cement paste using electrical impedance spectroscopy, Mater. Struct. 46 (5) (2013) 697–708. [109] J.-M. Loche, A. Ammar, P. Dumargue, Influence of the migration of chloride ions on the electrochemical impedance spectroscopy of mortar paste, Cement Concr. Res. 35 (9) (2005) 1797–1803. [110] B. Dong, Z. Gu, Q. Qiu, Y. Liu, W. Ding, F. Xing, et al., Electrochemical feature for chloride ion transportation in fly ash blended cementitious materials, Constr. Build. Mater. 161 (2018) 577–586. [111] J. Lizarazo-Marriaga, C. Higuera, P. Claisse, Measuring the effect of the ITZ on the transport related properties of mortar using electrochemical impedance, Constr. Build. Mater. 52 (2014) 9–16. [112] J.-S.M. Lee, M.E. Briggs, C.-C. Hu, A.I. Cooper, Controlling electric double-layer capacitance and pseudocapacitance in heteroatom-doped carbons derived from hypercrosslinked microporous polymers, Nano Energy 46 (2018) 277–289. [113] J.N. Neal, D.J. Wesolowski, D. Henderson, J. Wu, Electric double layer capacitance for ionic liquids in nanoporous electrodes: effects of pore size and ion composition, J. Mol. Liq. 270 (2018) 145–150. [114] A. Moya, The differential capacitance of the electric double layer in the diffusion boundary layer of ion-exchange membrane systems, Electrochim. Acta 178 (2015) 249–258. [115] X. Hu, C. Shi, X. Liu, J. Zhang, G. Schutter, A review on microstructure characterization of cement-based materials subjected to chloride by AC impedance, 4th Int. Conference on Sustainable Construction Materaisl and Technology. Las Vegas Nevada, USA, 7-11 August, 2016, pp. 1–11. [116] M. Sánchez, J. Gregori, C. Alonso, J. García-Jareño, H. Takenouti, F. Vicente, Electrochemical impedance spectroscopy for studying passive layers on steel rebars immersed in alkaline solutions simulating concrete pores, Electrochim. Acta 52 (27) (2007) 7634–7641. [117] C.-Q. Ye, R.-G. Hu, S.-G. Dong, X.-J. Zhang, R.-Q. Hou, R.-G. Du, et al., EIS analysis on chloride-induced corrosion behavior of reinforcement steel in simulated carbonated concrete pore solutions, J. Electroanal. Chem. 688 (2013) 275–281. [118] B. Dong, Y. Wang, W. Ding, S. Li, N. Han, F. Xing, et al., Electrochemical impedance study on steel corrosion in the simulated concrete system with a novel self-healing microcapsule, Constr. Build. Mater. 56 (2014) 1–6. [119] M. Montemor, A. Simoes, M. Salta, Effect of fly ash on concrete reinforcement corrosion studied by EIS, Cement Concr. Compos. 22 (3) (2000) 175–185. [120] C.G. Berrocal, K. Hornbostel, M.R. Geiker, I. Löfgren, K. Lundgren, D.G. Bekas, Electrical resistivity measurements in steel fibre reinforced cementitious materials, Cement Concr. Compos. 89 (2018) 216–229. [121] W.J. McCarter, G. Starrs, T.M. Chrisp, P.F. Banfill, Complex impedance and dielectric dispersion in carbon fiber reinforced cement matrices, J. Am. Ceram. Soc. 92 (7) (2009) 1617–1620. [122] V. Feliu, J. González, C. Andrade, S. Feliu, Equivalent circuit for modelling the steel-concrete interface. I. Experimental evidence and theoretical predictions, Corros. Sci. 40 (6) (1998) 975–993. [123] V. Feliu, J. González, C. Adrade, S. Feliu, Equivalent circuit for modelling the steelconcrete interface. II. Complications in applying the stern-geary equation to corrosion rate determinations, Corros. Sci. 40 (6) (1998) 995–1006. [124] S.J. Ford, T.O. Mason, Combined bulk and interfacial studies of the cement/steel system by impedance spectroscopy, Techniques to Assess the Corrosion Activity of Steel Reinforced Concrete Structures: ASTM International, 1996. [125] M. Torres-Luque, E. Bastidas-Arteaga, F. Schoefs, M. Sánchez-Silva, J.F. Osma, Non-destructive methods for measuring chloride ingress into concrete: state-ofthe-art and future challenges, Constr. Build. Mater. 68 (2014) 68–81. [126] S.B. Aoun, M. Bouklah, K. Khaled, B. Hammouti, Electrochemical impedance spectroscopy investigations of steel corrosion in acid media in the presence of thiophene derivatives, Int J Electrochem Sci. 11 (2016) 7343–7358. [127] M. Stern, A.L. Geary, Electrochemical polarization I. A theoretical analysis of the shape of polarization curves, J. Electrochem. Soc. 104 (1) (1957) 56–63. [128] J. Wei, X. Fu, J. Dong, W. Ke, Corrosion evolution of reinforcing steel in concrete under dry/wet cyclic conditions contaminated with chloride, J. Mater. Sci. Technol. 28 (10) (2012) 905–912. [129] M.S. Konsta-Gdoutos, G. Batis, P.A. Danoglidis, A.K. Zacharopoulou, E.K. Zacharopoulou, M.G. Falara, et al., Effect of CNT and CNF loading and count on the corrosion resistance, conductivity and mechanical properties of nanomodified OPC mortars, Constr. Build. Mater. 147 (2017) 48–57. [130] B. Pradhan, B. Bhattacharjee, Performance evaluation of rebar in chloride contaminated concrete by corrosion rate, Constr. Build. Mater. 23 (6) (2009) 2346–2356. [131] L. Hachani, C. Fiaud, E. Triki, A. Raharinaivo, Characterisation of steel/concrete interface by electrochemical impedance spectroscopy, Br. Corros. J. 29 (2) (1994) 122–127. [132] D. John, P. Searson, J. Dawson, Use of AC impedance technique in studies on steel in concrete in immersed conditions, Br. Corros. J. 16 (2) (1981) 102–106. [133] G. Qiao, J. Ou, Corrosion monitoring of reinforcing steel in cement mortar by EIS and ENA, Electrochim. Acta 52 (28) (2007) 8008–8019. [134] L. Dhouibi, E. Triki, A. Raharinaivo, The application of electrochemical impedance

[73] M. Cabeza, P. Merino, X. Nóvoa, I. Sánchez, Electrical effects generated by mechanical loading of hardened Portland cement paste, Cement Concr. Compos. 25 (3) (2003) 351–356. [74] Y. Li, C. Sui, Q. Ding, Study on the cracking process of cement-based materials by AC impedance method and ultrasonic method, J. Nondestruct. Eval. 31 (3) (2012) 284–291. [75] P. Gu, Z. Xu, P. Xie, J. Beaudoin, An AC impedance spectroscopy study of microcracking in cement-based composites during compressive loading, Cement Concr. Res. 23 (3) (1993) 675–682. [76] B. Han, K. Zhang, X. Yu, E. Kwon, J. Ou, Electrical characteristics and pressuresensitive response measurements of carboxyl MWNT/cement composites, Cement Concr. Compos. 34 (6) (2012) 794–800. [77] A. Peled, J.M. Torrents, T.O. Mason, S.P. Shah, E.J. Garboczi, Electrical impedance spectra to monitor damage during tensile loading of cement composites, ACI Mater. J. 98 (4) (2001) 313–322. [78] W. Li, W. Ji, G. Fang, Y. Liu, F. Xing, Y. Liu, et al., Electrochemical impedance interpretation for the fracture toughness of carbon nanotube/cement composites, Constr. Build. Mater. 114 (2016) 499–505. [79] M. Pour-Ghaz, M. Niemuth, J. Weiss, Use of electrical impedance spectroscopy and conductive surface films to detect cracking and damage in cement based materials, Spec. Publ. 292 (2013) 1–16. [80] P. Gu, P. Xie, J. Beaudoin, Impedance characterization of microcracking behaviour in fibre-reinforced cement composites, Cement Concr. Compos. 15 (3) (1993) 173–180. [81] B. Tamtsia, J. Beaudoin, J. Marchand, A coupled AC impedance—creep and shrinkage investigation of hardened cement paste, Mater. Struct. 36 (3) (2003) 147. [82] J. Torrents, T. Mason, E.J. Garboczi, Impedance spectra of fiber-reinforced cement-based composites: a modeling approach, Cement Concr. Res. 30 (4) (2000) 585–592. [83] J. Torrents, T. Mason, A. Peled, S. Shah, E.J. Garboczi, Analysis of the impedance spectra of short conductive fiber-reinforced composites, J. Mater. Sci. 36 (16) (2001) 4003–4012. [84] T. Mason, M. Campo, A. Hixson, L. Woo, Impedance spectroscopy of fiber-reinforced cement composites, Cement Concr. Compos. 24 (5) (2002) 457–465. [85] S. Wansom, N. Kidner, L. Woo, T. Mason, AC-impedance response of multi-walled carbon nanotube/cement composites, Cement Concr. Compos. 28 (6) (2006) 509–519. [86] N. Ozyurt, L.Y. Woo, T.O. Mason, S.P. Shah, Monitoring fiber dispersion in fiberreinforced cementitious materials: comparison of AC-impedance spectroscopy and image analysis, ACI Mater. J. 103 (5) (2006) 340. [87] N. Ozyurt, T.O. Mason, S.P. Shah, Correlation of fiber dispersion, rheology and mechanical performance of FRCs, Cement Concr. Compos. 29 (2) (2007) 70–79. [88] N. Ozyurt, T.O. Mason, S.P. Shah, Non-destructive monitoring of fiber orientation using AC-IS: an industrial-scale application, Cement Concr. Res. 36 (9) (2006) 1653–1660. [89] S. Hong, R.S. Harichandran, Sensors to monitor CFRP/concrete bond in beams using electrochemical impedance spectroscopy, J. Compos. Constr. 9 (6) (2005) 515–523. [90] K. Kurumisawa, T. Nawa, Effect of microstructure and moisture content on the electric conductivity of hardened cement paste, Proc. SCMT 3 (2013). [91] J.M. Ortega, I. Sánchez, M. Climent, Impedance spectroscopy study of the effect of environmental conditions in the microstructure development of OPC and slag cement mortars, Arch. Civ. Mech. Eng. 15 (2) (2015) 569–583. [92] J.M. Ortega, A. Albaladejo, J. Pastor, I. Sánchez, M. Climent, Influence of using slag cement on the microstructure and durability related properties of cement grouts for micropiles, Constr. Build. Mater. 38 (2013) 84–93. [93] S. Perron, J. Beaudoin, Freezing of water in portland cement paste–an ac impedance spectroscopy study, Cement Concr. Compos. 24 (5) (2002) 467–475. [94] T. Sato, J.J. Beaudoin, Coupled AC impedance and thermomechanical analysis of freezing phenomena in cement paste, Mater. Struct. 44 (2) (2011) 405–414. [95] T. Sato, J. Beaudoin, An AC impedance spectroscopy study of freezing phenomena in wollastonite micro-fibre reinforced cement paste, Proceedings of the International Symposium on Role of Cement Science in Sustainable Development, Scotland, UK, Sep 2003, pp. 3–4. [96] S. Zhong, M. Shi, Z. Chen, A study of polymer-modified mortars by the AC impedance technique, Cement Concr. Res. 32 (6) (2002) 979–982. [97] T. Zhang, O.E. Gjørv, An electrochemical method for accelerated testing of chloride diffusivity in concrete, Cement Concr. Res. 24 (8) (1994) 1534–1548. [98] T. Sugiyama, T. Bremner, Y. Tsuji, Determination of chloride diffusion coefficient and gas permeability of concrete and their relationship, Cement Concr. Res. 26 (5) (1996) 781–790. [99] Z. Liu, J. Beaudoin, An assessment of the relative permeability of cement systems using AC impedance techniques, Cement Concr. Res. 29 (7) (1999) 1085–1090. [100] Z. Liu, J. Beaudoin, The permeability of cement systems to chloride ingress and related test methods, Cem. Concr. Aggregates 22 (1) (2000) 16–23. [101] A. Aït-Mokhtar, O. Poupard, P. Dumargue, Relationship between the transfer properties of the coating and impedance spectroscopy in reinforced cement-based materials, J. Mater. Sci. 41 (18) (2006) 6006–6014. [102] A.J. Bard, L.R. Faulkner, J. Leddy, C.G. Zoski, Electrochemical Methods: Fundamentals and Applications, wiley, New York, 1980. [103] B. Díaz, X. Nóvoa, M. Pérez, Study of the chloride diffusion in mortar: a new method of determining diffusion coefficients based on impedance measurements, Cement Concr. Compos. 28 (3) (2006) 237–245. [104] H. Mercado, S. Lorente, X. Bourbon, Chloride diffusion coefficient: a comparison between impedance spectroscopy and electrokinetic tests, Cement Concr. Compos.

13

Cement and Concrete Composites 100 (2019) 1–14

X. Hu, et al.

[135]

[136] [137]

[138]

[139]

[140]

[141]

[142]

651–656. [143] M. Shi, Z. Chen, Low frequency characteristic of impedance spectroscopy of concrete, J. Chin. Ceram. Soc. 24 (6) (1996) 703–706. [144] S. Ford, J. Shane, T. Mason, Assignment of features in impedance spectra of the cement-paste/steel system, Cement Concr. Res. 28 (12) (1998) 1737–1751. [145] L.Y. Woo, Characterizing Fiber-Reinforced Composite Structures Using ACImpedance Spectroscopy, AC-IS, 2005. [146] D. Edwards, J.-H. Hwang, S. Ford, T. Mason, Experimental limitations in impedance spectroscopy: Part V. Apparatus contributions and corrections, Solid State Ionics 99 (1–2) (1997) 85–93. [147] F. He, R. Wang, C. Shi, C. Chen, L. Lin, X. An, Error evaluation and correction of stray impedance during measurement and interpretation of AC impedance of cement-based materials, Cement Concr. Compos. 72 (2016) 190–200. [148] J.R. Macdonald, E. Barsoukov, Impedance spectroscopy: theory, experiment, and applications, History 1 (8) (2005) 1–13. [149] W. McCarter, G. Starrs, T. Chrisp, Electrical conductivity, diffusion, and permeability of Portland cement-based mortars, Cement Concr. Res. 30 (9) (2000) 1395–1400. [150] C.-N. Cao, J.-Q. Zhang, An Introduction to Electrochemical Impedance Spectroscopy. Science, Beijing vol. 21, (2002). [151] F. He, R. Wang, R. Zhang, C. Chen, L. Lin, Effect of the sample–electrode contact impedance on the appearance of dispersion in the AC impedance spectroscopy of cement-based materials, J. Sustain. Cem. Base Mater 7 (6) (2018) 1–17.

spectroscopy to determine the long-term effectiveness of corrosion inhibitors for steel in concrete, Cement Concr. Compos. 24 (1) (2002) 35–43. B. Dong, Q. Qiu, J. Xiang, C. Huang, H. Sun, F. Xing, et al., Electrochemical impedance interpretation of the carbonation behavior for fly ash–slag–cement materials, Constr. Build. Mater. 93 (2015) 933–942. Q. Qiu, Z. Gu, J. Xiang, C. Huang, B. Dong, Carbonation study of cement-based material by electrochemical impedance method, ACI Mater. J. 114 (4) (2017). C. Xiong, L. Jiang, Y. Zhang, H. Chu, P. Jiang, Characterization of sulfate diffusion into cement paste by low frequency impedance spectroscopy, Mater. Lett. 174 (2016) 234–237. L. Kong, L. Hou, Y. Wang, G. Sun, Investigation of the interfacial transition zone between aggregate-cement paste by AC impedance spectroscopy, J. Wuhan Univ. Technol.-Materials Sci. Ed. 31 (4) (2016) 865–871. F. He, R. Wang, R. Zhang, C. Chen, L. Lin, X. An, Evaluation of sample-electrode contact impedance in two-point measured AC impedance spectroscopy of cementbased materials, Int. J. Mater. Sci. Appl. 7 (3) (2018) 106. M. Cabeza, M. Keddam, X. Nóvoa, I. Sánchez, H. Takenouti, Impedance spectroscopy to characterize the pore structure during the hardening process of Portland cement paste, Electrochim. Acta 51 (8–9) (2006) 1831–1841. C. Alonso, C. Andrade, M. Keddam, X. Novoa, H. Takenouti, Study of the dielectric characteristics of cement paste, Mater. Sci. Forum: Trans. Tech. Publ. (1998) 15–28. L. WU, P. YAN, Review on AC impedance techniques for chloride diffusivity determination of cement-based materials, J. Chin. Ceram. Soc. 40 (5) (2012)

14