Non-contact Impedance Measurement Research Articles

In situ monitoring of hydration of magnesium oxysulfate cement paste: Effect of MgO/MgSO4 ratio

This work systematically investigated the early hydration process of magnesium oxysulfate (MOS) cement pastes by non-contact impedance measurement (NCIM) and other microstructural tests. According to the evolution of impedance response, the hydration process of MOS cement pastes can be divided into three stages (dissolution, acceleration and hardened stages). The identification of hydration is strongly related to the transformation of solid phases and alkalinity of pastes. The presence and crystalline degrees of 517 phase and 318 phase are evaluated by DTG and XRD tests, respectively. It seems that MgO/MgSO4 ratio does not affect crystalline degree of hydrated products much. MH crystals and cracks are considered to result in the low mechanical strength of MOS cement paste. It can be inferred from experimental results that NCIM is a good method to analyze the hydration evolution of MOS cement pastes in-situ.

In situ monitoring of pore structure of magnesium oxysulfate cement paste: Effect of MgSO4/H2O ratio

This work systematically presented the pore structure evolution of different magnesium oxysulfate (MOS) cement pastes by non-contact impedance measurement (NCIM), fractal theory and other microstructural experiments. According to the evolution of electrical impedance response, three hydration stages (dissolution, acceleration and hardened stages) can be identified in the pastes. Furthermore, based on the results obtained from NCIM and fractal theory, the porosity, incremental pore volume, pore tortuosity, average pore diameter and maximal pore diameter of MOS cement pastes are investigated. The influence of MgSO4/H2O ratio on pore structure of MOS cement paste is primarily explained. It can be inferred from predicted and experimental results that NCIM is a good method to analyze the microstructure evolution of MOS cement pastes in-situ.

The investigation of early hydration and pore structure for limestone powder wastes blended cement pastes

This work systematically investigates the early hydration process and pore structure evolution of high limestone powder wastes content blended cement pastes by non-contact impedance measurement and microstructural tests. According to the evolution of impedance response, the early hydration process of blende cement pastes can be divided into four stages, denominated as dissolution, acceleration, dynamic balance and hardened stages, respectively. Dynamic balance stage not present in hydration process of pure cement, is a characteristic hydration stage for blended cement pastes. Furthermore, fractal approach for predicting the evolution of pore structure is proposed originally, based on the impedance results.

The early hydration of metakaolin blended cements by non-contact impedance measurement

This paper aims to study the early-age hydration process of metakaolin blended cement pastes. The hydration characteristics of different stages, i.e. first dissolution, acceleration, second dissolution and hardened stage, are analyzed by non-contact impedance measurement (NCIM), X-ray diffraction (XRD), derivative thermogravimetric analysis test (DTG), and Fourier transform infrared spectroscopy (FTIR). Through the comprehensive investigation, the second dissolution stages corresponding to the plateau segments appearing in impedance modulus curves for metakaolin blended cement pastes, seem to be associated with the dissolution behavior of metakaolin in alkaline condition. The larger amount of metakaolin in the paste results in the more distinct plateau or descent segment. Furthermore, 15% metakaolin replacement is most favorable to enhance the hydration rate and broaden the range of pore size distribution of blended cement paste. Meanwhile, the compressive strength, water requirement of normal consistency and setting time of blended pastes are examined to study their macro-physical performances.

CONTINUOUS MICROSTRUCTURAL CORRELATION OF SLAG/SUPERPLASTICIZER CEMENT PASTES BY HEAT AND IMPEDANCE METHODS VIA FRACTAL ANALYSIS

This paper presents a preliminary work to evaluate the influence of slag and superplasticizer on the early-age hydration of cement pastes by an innovative non-contact impedance measurement, heat evolution method, compressive strength and setting time tests. Besides, the cumulative pore volume obtained from modulus and phase of impedance in different hydration sections is taken to continuously correlate the cumulative heat releasing of cement pastes via the fractal analysis. Retarded phenomena and mechanism of hydration in cement pastes incorporated with slag and superplasticizer are studied, respectively. It is found that the compressive strength and setting time have a good linear relation with the slag amount in blended cement pastes.

Hydration process of fly ash blended cement pastes by impedance measurement

This study focuses on the early-age hydration development in fly ash blended cement pastes. The characteristic features in different hydration stages and the evolution of zeolites phase, viz., gismondine, are identified in high-dosage fly ash blended cement-based materials using the innovative non-contact impedance measurement (NCIM), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), heat evolution test and pore solution analysis. It is found that the zeolite formation stage is comparatively distinct at the late hydration period. Besides, the influence of fly ash dosages in cement pastes on setting time and compressive strength are further examined.

Hydration stage identification and phase transformation of calcium sulfoaluminate cement at early age

This paper studies hydration stages and phase transformation mechanism of fresh calcium sulfoaluminate (CSA) cement. Features of different hydration stages of CSA cement paste are identified by non-contact impedance measurement (NCIM), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), heat evolution test, ion chromatograph and inductively coupled plasma. Ettringite (AFt) and monosulfate (AFm) are found as metastable phases and have poor crystallization degree at the early-age hydration. The unique transformation between AFt and AFm is observed. The influence of different w/c ratios is further studied by NCIM, setting time and compressive strength test.

A fractal approach to determine thermal conductivity in cement pastes

This paper presents a preliminary work to evaluate the thermal conductivity performance in pure and blended cement pastes with fly ash, slag and silica fume. The thermal conductivity of cement pastes cured in saturated and dry status with different hydration ages are also measured and predicted by quick thermal conductivity meter (QTM) and innovative non-contact impedance measurement (NCIM) based on a newly proposed fractal model. Besides, a corresponding simulation of fractal-like network is developed to evaluate the influences of pore structure parameters, intrinsic thermal conductivity coefficients of solid and water or gas phase on thermal conductivity performance of cement pastes.

Characterization of early-age hydration process of cement pastes based on impedance measurement

This paper investigates the hydration process of cement pastes using an isothermal calorimetry, Fourier transforms infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis and non-contact impedance measurement (NCIM). The reliability of impedance data from NCIM is checked by classical Kramers–Kronig transformation. Hydration behaviors of pure cement paste in different stages (dissolution, competition and acceleration stages) are interpreted by FTIR, XRD and NCIM. Influences of water to cement ratios, fly ash, slag, silica fume and curing temperature are investigated by compressive strength test and NCIM. It is found that the compressive strength and impedance data have a good linear relationship.

Permeability interpretation for young cement paste based on impedance measurement

This paper evaluates the permeability assessment of young cement pastes using innovative Non-Contact Impedance Measurement (NCIM). A fractal permeability model based on NCIM is proposed in this work. The permeability value of young cement pastes can be measured non-destructively and continuously with hydration by means of this model and NCIM. Furthermore, a fractal simulation is conducted to study the influence of porosity, minimal and maximal pore sizes on permeability. From the comparison of experimental and simulated results, the fractal model and simulation based on NCIM may provide an alternative way to evaluate the permeability of young cement-based materials in situ.

Impedance measurement to characterize the pore structure in Portland cement paste

This paper proposes an alternative way to characterize the pore structure in cement pastes using an innovative non-contact impedance measurement. This methodology is based on the pore fractal theory: the fractal dimension for pore space is solved from two networks (fractal electrical network and pore structure network); the minimal pore diameter in the pore fractal theory is evaluated from electrical double layers model; the applicable scope of non-contact impedance measurement is addressed through frequency dispersion mechanism. Through the pore fractal theory and this impedance measurement, the relationship between the cumulative pore volume and impedance response of cement pastes is revealed.

New Pore Structure Assessment Methods for Cement Paste

AbstractIn this study, two new approaches for pore structure assessment of cement paste are investigated and compared with mercury intrusion porosimetry (MIP)-based methods. One is based on a status-oriented computer model; the other is based on fractal analysis on the impedance measured by a noncontact impedance measurement system. In the computer model, cement paste microstructure is simulated as a function of cement properties, water-to-cement ratio (w/c), and degree of hydration. With the simulated microstructure, large capillary pores are characterized by image processing. A model developed based on nitrogen adsorption results and physical rules is applied to predict the small capillary pore structure, as a complementation to cover the whole range of capillary pores. In the impedance measurement based approach, fractal dimensions corresponding to specific pore size ranges are determined from the fractal networks and the impedance responses of the material. Then the pore size distribution curves are d...

Lineshapes, shifts and broadenings in dynamical X-ray photoelectron spectroscopy

We describe in detail a model that can be used to estimate the X-ray photoelectron spectroscopic data of surfaces when a time varying bias or a modulation of the electrical properties of the surface is applied by external stimulation, in the presence of a neutralizing electron beam. Using the model and spectra recorded under periodic sample bias modulation, certain electronic properties related to charging dynamics of the surface can be estimated. The resulting technique is a non-contact impedance measurement technique with chemical specificity. Typical behavior of spectra under a square wave bias is given. Alternative modulation schemes are investigated, including small-signal square wave modulation, sinusoidal modulation and modulation of sample resistivity under fixed bias.