Non-contact Electrical Resistivity Measurement Research Articles

Resistivity and chloride diffusion coefficient of cement-based materials characterized by non-contact electrical resistivity method and resistivity model

The present study involves the application of the non-contact electrical resistivity measurement (NC-ERM) as a non-destructive method to continuously and in-situ measure the resistivity changes of cement-based materials. The NC-ERM was enhanced and utilized to evaluate the resistivity of the materials, and the steady-state chloride diffusion coefficients of various types of cement-based materials were experimentally determined. The results revealed that the highest resistivity was observed in mortar with a sand-to-cement ratio of 1.0 and concrete with an aggregate-to-cement ratio of 0.6, and the steady-state chloride diffusion coefficient increased with the concentration of the pore solution. Furthermore, a novel multi-level series-parallel model was developed to predict the resistivity and steady-state chloride diffusion coefficient of cement-based materials, with calculated values differing by 5% or less. The calculated chloride diffusion coefficient closely matched the value obtained from NC-ERM, indicating the satisfactory accuracy of the non-destructive experiment and theoretical calculation model.

Non-destructive characterization of pore structure and chloride diffusion coefficient of cementitious materials with modified non-contact electrical resistivity method

The intricate pore structure of cement-based materials passively influences chloride ion transport and mechanical properties. Existing non-contact electrical resistivity measurement (NC-ERM) methods lack precision for rigorous studies. the NC-ERM was upgraded in this research, which is suitable for assessing the pore structure and transport characteristics of hardened cementitious substrates. The results obtained from this method closely correspond to those obtained from CEMHYD3D, Mercury intrusion porosimetry (MIP), and other methods. Additionally, the impact of mixture proportions on the resistivity, pore structure parameters, and chloride ion diffusion coefficient of cementitious materials is discussed. With an increase in sand ratio and sand-to-stone ratio, the resistivity exhibits an initial rise followed by a decline. Chloride diffusion of 5 wt% NaCl-saturated specimens is 1.2–1.3 times higher than 3.5 wt% NaCl. This study provides a novel non-destructive, convenient and accurate method for characterising the pore structure and testing the transport properties of cementitious materials.

A study on the hydration of calcium aluminate cement pastes containing silica fume using non-contact electrical resistivity measurement

In this study, a non-contact electrical resistivity method is employed to investigate the hydration process of calcium aluminate cement (CAC) pastes incorporating silica fume (SF) at an early age. The CAC-SF pastes have a water-to-binder ratio (w/b) of 0.6 and a replacement of SF for CAC at 0, 5, 10, and 20% (by weight of the binder). The pastes are tested for electrical resistivity, thermal analysis (internal temperature), setting time, and compressive strength, and the hydration products of the pastes are also examined. The results indicate that the evolution of electrical resistivity is closely related to the hydration process of the CAC pastes, and the conversion stage is closely associated with the setting time of pastes. As the increase of SF replacement, the hydration process of CAC pastes was accelerated within 24 h, and the development of compressive strength was hampered at an early age but increased later. SF replacement inhibits the conversion of metastable CAC hydrates (CAH10 and C2AH8) to C3AH6 through filling, seeding, and reacting with CAC, thus reducing the heat of hydration.

Assessment of Electrical Resistivity and Oxygen Diffusion Coefficient of Cementitious Materials from Microstructure Features

A newly proposed modified non-contact electrical resistivity measurement was used to test the resistivity of concrete and cement mortar. The oxygen diffusion coefficients of concrete and mortar were determined by a gas diffusion measurement, and the capillary porosity of concrete and cement mortar was measured by mercury intrusion porosimetry (MIP) measurement. The obtained electrical resistivity and capillary porosity results were verified with other researchers’ data, the measured electrical resistivity results can be estimated by a simple equation from the capillary porosity results. The obtained oxygen diffusion coefficient results were quantitatively correlated with capillary porosity and electrical resistivity measurement results. The proposed equations can be practically used to assess the electrical resistivity and oxygen diffusion coefficient.

Correlating the Chloride Diffusion Coefficient and Pore Structure of Cement-Based Materials Using Modified Noncontact Electrical Resistivity Measurement

AbstractThe electrical resistivity of hardened cement-based materials was measured in this work by a modified noncontact electrical resistivity measurement (MN-CM). The resistivity was further proc...

Determining porosity and pore network connectivity of cement-based materials by a modified non-contact electrical resistivity measurement: Experiment and theory

A modified non-contact electrical resistivity measurement is proposed to determine porosity and pore network connectivity of cement-based materials. The porosity of mortar with different water-to-cement ratios was tested by mercury intrusion porosimetry (MIP) and the tortuosity was calculated from pore entrapment volume fraction. The relationship between pore structure and resistivity was studied using the three most commonly used theories. It was observed that the multi-phase phenomenological model can indicate the effect of porosity and pore connectivity on the resistivity of cement-based materials. The parameter m in Archie's Law as an index of pore connectivity can be expressed as a variable that varies with the tortuosity. The parameters in the GEM model are closely related to the nature of the material: the parameter M should be related to the composition of the material and the degree of hydration of the cement, and the parameter t is a variable that varies with the pore connectivity. Based on these theories, equations are derived to correlate the porosity and pore network connectivity to the formation factor of cement based materials. The developed approach thus has a potential to be used as a simple and effective tool for pore structure investigation of cement based materials.

Critical features of microstructure development of early-age cement paste revealed by non-contact electrical resistivity measurement

The microstructure evolution of cement paste governs the material properties on the macrostructural level. Recently, a non-contact electrical resistivity measurement has been applied to study the pore structure evolution of early-age cement-based materials. In this study, the capillary pore tortuosity development of early-age cement paste is predicted by the non-contact electrical resistivity measurement. The results demonstrate that the capillary pore tortuosity of cement paste evolves slightly at the first few hours but begins to increase substantially at the percolation threshold of the hard core/soft shell (HCSS) particles. By coupling the predicted evolution with the HCSS model, it is found that the capillary porosity and the thickening rate of the hydration product shell increase with the increase of the water to cement (w/c) ratio. Early-age C-S-H gel is revealed to grow in a lengthened manner, and the greater is the w/c ratio, the more elongated is the C-S-H gel. The juxtaposition of the nanometre-sized elementary bricks is the hidden force for the elongated growth of C-S-H gel. It is disclosed that the initial distance between cement particles is a fundamental factor that governs the microstructure development of cement paste. The hydration of cement preferentially achieves the particle percolation, and the hydration products grow more loosely when the initial distance between cement particles is greater.

Study on the hydration parameters in hardening paste, mortar and concrete based on electrical resistivity measurement

Specimens of fresh paste, mortar and concrete with W/C ratios of 0.30, 0.35, 0.40, 0.45, 0.50 and 0.55 were prepared to monitor electrical resistivity for a period of 24 h from casting using non-contact electrical resistivity measurement. A general equation $$\rho (t) = K_{\text{P}} \left( {1 - V_{\text{a}} } \right)^{ - m} \ln (Dt)$$ was obtained from the electrical resistivity development of the mixtures during the decelerating period of the hydration process, and the physical meanings of the parameters in the general equation were identified. The densification rate of the hydration system was obtained from the slope of electrical resistivity development with time, and the hydration rate of each cement particle in unit volume of the cement paste matrix was identified. The influence of aggregate and W/C on the parameters was analyzed. The same aggregate volume fraction was used in all of the mortar and concrete samples. A mortar sample has a faster densification rate than that of a concrete sample at each W/C due to the higher specific surface area of the total aggregate particles in the mortar, resulting in a higher tortuosity for the ions migration. The very close D values of the pastes, the mortars and the concretes with the same W/C, and the slightly increasing trend with W/C, present the characteristics of the hydration rate of each cement particle in unit volume of the cement paste matrix. Mixtures with lower W/C have higher densification rates, and the quantitative relationships were obtained for the paste, mortar and concrete samples, respectively. The densification rate of a mixture can be used as an index for deriving its W/C based on the quantitative relationship obtained from electrical resistivity measurement. The densification rate of a hydration system and the hydration rate of each cement particle in the hydration system, as important hydration parameters, can help to reveal the hydration kinetics that are correlated with hardening properties of concrete.

Experimental study on chloride permeability in concrete by non-contact electrical resistivity measurement and RCM

A new non-contact electrical resistivity (NC-ER) measurement technique was proposed to measure the chloride diffusion coefficient of cement-based materials, and the results from testing were compared with the rapid chloride migration test, traditionally called RCM. Cement pastes with water cement ratios of 0.30, 0.35 and 0.40, and concrete with a water cement ratio of 0.4 were prepared for the chloride diffusion coefficient measurement by the two methods.The chloride diffusion coefficient results obtained by both approaches show a reasonable decrease with hydration age and increase with the increase of water cement ratio. The results for the pastes from the RCM test are in range of (0.69∼3.15)×10−7cm2/s at 3d∼80d, and the results from the NC-ER test are in the range of (0.53∼1.71)×10−7cm2/s., which are of the same order of magnitude and follow a linear relationship DRCM=1.8821DNC-ER−0.3506 (R2=0.9205).From the NC-ER test, the chloride diffusion coefficient of concrete C0.4 is lower than that of paste P0.3 at the same ages and was verified by the porosity and formation factor analysis, while the RCM test obtained opposite trends. A better linear correlation between the chloride diffusion coefficient of the concrete and paste samples was obtained based on the NC-ER test. It can be deduced that the NC-ER set-up has advantages over the RCM set-up in measuring the chloride diffusion coefficient of concrete, such as there being no electrodes in the NC-ER setup which eliminates errors, and taking a much shorter time (about 5min) to complete a test.

Characterising cement carbonation curing using non-contact electrical resistivity measurement

Carbonation curing of cement paste and concrete promotes early strength gain, improves durability and recycles carbon dioxide in a beneficial manner. To examine the carbonation curing mechanism, fresh cement pastes and concretes subject to carbonation are characterised using a non-contact electrical resistivity measurement method. Resistivity measurements reveal that characteristic features of the hydration accelerated by carbonation are different from conventional hydration. The typical induction period is absent in the carbonation curing owing to the rapid precipitation of calcium carbonate. The resistivity measurement method produces a superimposed result of early hardening and multiple instances of progressive hardening by carbonation curing. The electrical resistivity is 3–6 times higher in the carbonated cement paste and about 8–16 times higher in the carbonated concretes in comparison with the hydration references. The carbonated lightweight concrete shows lower bulk resistivity than the carbonated normal-weight concrete, possibly owing to the release of internal water from the lightweight aggregates during carbonation. This is evidence of internal curing by lightweight aggregates.

Hydration of cement with retarder characterized via electrical resistivity measurements and computer simulation

Development of the electrical resistivity with time was measured for cement pastes with the addition of citric acid monohydrate (0%, 0.03%, 0.05% and 0.07%) using a non-contact electrical resistivity measurement device. As the retarder content increases, the electrical resistivity becomes larger in the dissolution and precipitation period but smaller after the setting period because of the protective layer formed around the clinker grains. The setting-time test confirmed that the time of the second peak in the curve of the electrical-resistivity development rate can reflect the setting behavior of the pastes. The time of the third peak in the curve of the electrical-resistivity development rate reflects the transition from a phase-boundary mechanism to a diffusion-controlled mechanism during cement hydration, and thus it was treated as the critical time in a computer simulation of the cement hydration. The computer simulation enabled the visualization of the microstructural evolution and the development of the hydration degree and porosity with time. The simulated results demonstrate the strong retarding effect of citric acid on cement hydration in the early stage. The hydration degree determined by the simulation is in consistent with the results of a non-evaporable water test. The microstructural observations obtained via scanning electron microscopy (SEM) show that the retarder delays cement hydration during the early stage, which confirms the findings of the computer simulation.

Mechanical and Microstructure Characterization of Fresh High- and Normal- Strength Concrete with Non-Contact Electrical Resistivity Measurement

This paper reports the investigation on both high and normal strength concrete using a non-contact electrical resistivity facility. The bulk resistivity development (ρ(t)-t curves) of the fresh concretes was evaluated from casting to 72h. The relationship between the electrical resistivity and the pore structure obtained from mercury intrusion porosimetry (MIP) method was analyzed. And the compressive strength evolution of fresh high- and normal- strength concrete was studied based on the bulk resistivity at early ages. The experiment results indicated a linear relationship between the fractional porosity and electrical resistivity. A further correlation between the compressive strength and electrical resistivity was analyzed with Archie’s law. Based on these studies, it appears that the electrical resistivity test could provide information for the design, quality control, quality assurance, and utilization of both high- and normal- strength concrete.

Application of GEM Equation in Microstructure Characterization of Cement-Based Materials

This study proposes an analytical model to relate the evolving microstructure of neat cement paste during hydration to the electrical resistivity measurement. The model is based on the general effective media theory and considers the contributions of both the low-resistivity phase (capillary pores) and the high-resistivity phase (gels and solids) in cement-pastes. The major parameters in the proposed model are the microstructural properties such as capillary pore percolation threshold and pore structure parameter, capillary pore phase and solid-gel phase resistivities. To validate the model, an empirical relationship between the resistivity formation factors and the phase volume fractions of a series of cement pastes has been built up with the assistance of noncontact electrical resistivity measurement and mercury intrusion porosimetry technique. The good agreement between the model and experimental data shows that it is feasible to obtain better understandings of the evolving microstructure of cement pas...

New Understanding of Cement Hydration Mechanism through Electrical Resistivity Measurement and Microstructure Investigations

The new understanding for the hydration mechanism of cement has been achieved based on the noncontact electrical resistivity measurement. The cement hydration process is divided into dissolution, dynamic balance, setting, hardening, and hardening deceleration stages according to the characteristic points on the electrical resistivity development curve p(t)-t and the differential curve dp(t)/dt-t. The microstructure analysis corresponding to each hydration stage is conducted with scanning electron microscope, x-ray diffraction, differential thermal analysis, and Fourier transform infrared spectroscopy techniques. This study provides the theoretical foundation for understanding the relationship between setting behavior, hardening properties, and resistivity development.

Early-age hydration of fresh concrete monitored by non-contact electrical resistivity measurement

This paper reports the investigations on the early hydration process of fresh concrete using a non-contact electrical resistivity measurement. The bulk resistivity development ( ρ( t)– t curves) and the pore solution resistivity development ( ρ 0( t)– t curves) of fresh concrete, with and without fly ash replacement, were obtained for the period from casting to the age of 48 h. The porosity development ( ϕ( t)– t curves) was obtained from the ρ( t)– t and ρ 0( t)– t evolution curves with the calculated initial porosity and the measured porosity at 1 day by mercury intrusion porosimetry (MIP). The degree of hydration ( α( t)– t) of the cement-based materials was then obtained based on the porosity change with time, which was caused by the increase of hydration products with a lower density as compared to that of the original cement in the hydration system. The comparison of the degree of hydration predicted from the porosities ( ϕ( t)– t) and obtained from the experimental measurement of non-evaporable water showed a good agreement of the two. The setting and hardening behavior of fresh concrete was characterized by the characteristic points on the ρ( t)– t and d ρ( t)/d t– t curves. The retarded hydration caused by the fly ash incorporation could be identified by the characteristic points.

Noncontact electrical resistivity measurement technique for molten metals

A noncontact technique of measuring the changes in electrical conductivity (or resistivity) of conducting liquids is reported. The technique is based on a conducting drop that is levitated by the high-temperature electrostatic levitator in a high vacuum. This technique, which utilizes the principle of the asynchronous induction motor, measures the relative changes in torque as a function of temperature by applying a rotating magnetic field to the sample. Changes in electrical resistivity are related to the changes in measured torque using the formula developed for the induction motor. Validity of this technique was demonstrated using a pure aluminum sample around its melting temperature. When the measurement results were calibrated by a literature value of resistivity at the melting point, our resistivity data around the melting point could be expressed by rliq=24.19+1.306×10−2(T−Tm) μΩ cm over Tm∼1160 K, rsolid=10.77+1.421×10−2(T−Tm) μΩ cm over 700 K∼Tm, and the thermal conductivity as determined by the Wiedemann–Franz–Lorenz law from the resistivity data was given by κliq(T)=94.61+4.41×10−2(T−Tm) W m−1 K−1, κsolid(T)=211.13−7.57×10−2(T−Tm) W m−1 K−1. Both electrical resistivity and thermal conductivity are in close agreement with the literature, confirming the validity of the present technique.