38 research outputs found

    An immittance spectroscopy study of cementitious materials during early hydration

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    Sensing of damage and repair of cement mortar using electromechanical impedance

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    Lead zirconium titanate (PZT) has recently emerged as a low-cost material for non-destructive monitoring for civil structures. Despite the numerous studies employing PZT transducers for structural health monitoring, no studies have assessed the effects of both damage and repair on the electromechanical impedance response in cementitious materials. To this end, this study was conducted to assess the effects of the damage and repair of mortar samples on the electromechanical response of a surface-mounted PZT transducer. When damage was introduced to the specimen in stages, the resonance frequencies of the admittance signature were shifted to lower frequencies as the damage increased, and an increase in the peak amplitude was detected, indicating an increase in the damping and a reduction in the material stiffness properties. Also, increasing the damage in the material has been shown to decrease the sensitivity of the PZT to further damage. During the repair process, a noticeable difference between the after-damage and the after-repair admittance signatures was noted. The root-mean-square deviation (RMSD) showed a decreasing trend during the repair process, when compared to the before repair RMSD response which indicated a partial recovery for the material properties by decreasing the damping property in the material

    A Combined Electrical and Electromechanical Impedance Study of Early-Age Strength Gain in Cement Mortars

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    From simple strain gauges to more sophisticated techniques such as acoustic emission and digital image correlation methods, a variety of non-destructive methods are proposed in the literature for inspecting civil structures. However, in addition to accuracy and simplicity, automation and timely data collection are the main requirements for an efficient in situ non-destructive testing technique. Electrical impedance and the electromechanical impedance tests of cementitious members, are perceived to be suitable candidates for fulfilling the simplicity, automation and accuracy requirements, hence providing an efficient yet relatively non-expensive remote monitoring system. Throughout the first 28 days of a cementitious composites age, significant gain of strength is typically developed. It is crucial during this period to characterize the in situ strength gain profile for both planning and quality control purposes. This study investigates the viability of both the electromechanical impedance technique and the electrical impedance spectroscopy technique as non-destructive strength testing methods. These were assessed against their ability to detect strength changes due to the ongoing hydration reaction in cementitious mortars conforming with BS EN 196-1:2016. Results from both techniques were compared with the compressive and flexural strengths. The electromechanical impedance was assessed in terms of the change in the electrical impedance signature response through time, which was obtained through surface attached PZT sensors. Concurrently the electrical impedance response was collected through embedded stainless-steel electrodes across the frequency range of 1–10 MHz. This study will act as a guide for selection of a suitable technique for in situ strength gain monitoring using electrical methods

    Crack growth and closure in cementitious composites: monitoring using piezoceramic sensors

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    Coupling piezoceramics with civil-structures represents an important approach for the development of cost-effective, fully automated damage detection systems. Such systems are particularly suited for integration with autonomic technologies for self-sensing and self-healing of cementitious members. Here we present a novel study investigating both the effect of damage (cracking) and crack-closure, on the electromechanical response of mortars, with surface attached Lead Zirconate Titanate (PZT) sensors. Transducer signals were interpreted using a new analytical procedure which effectively increases the sensitivity of the electromechanical technique for both damage and repair detection compared to conventional methods of analysing the PZT response. The frequency ranges most sensitive to the presence of damage, were demonstrated to be influenced by the distance to the sensors. Furthermore, for pre-cracked specimens, it was shown that the electromechanical impedance can act as an indirect method to detect crack-closures by detecting the increase in the efficacy of load transmission in the sample. This findings of this research will enable the cost-effective monitoring and initiation of repair for self-healing cementitious infrastructure, which is expected to pave the way for self-sensing / self-healing cementitious structures.</p

    A Combined Electrical and Electromechanical Impedance Study of Early-Age Strength Gain in Cement Mortars

    Get PDF
    From simple strain gauges to more sophisticated techniques such as acoustic emission and digital image correlation methods, a variety of non-destructive methods are proposed in the literature for inspecting civil structures. However, in addition to accuracy and simplicity, automation and timely data collection are the main requirements for an efficient in situ non-destructive testing technique. Electrical impedance and the electromechanical impedance tests of cementitious members, are perceived to be suitable candidates for fulfilling the simplicity, automation and accuracy requirements, hence providing an efficient yet relatively non-expensive remote monitoring system. Throughout the first 28 days of a cementitious composites age, significant gain of strength is typically developed. It is crucial during this period to characterize the in situ strength gain profile for both planning and quality control purposes. This study investigates the viability of both the electromechanical impedance technique and the electrical impedance spectroscopy technique as non-destructive strength testing methods. These were assessed against their ability to detect strength changes due to the ongoing hydration reaction in cementitious mortars conforming with BS EN 196-1:2016. Results from both techniques were compared with the compressive and flexural strengths. The electromechanical impedance was assessed in terms of the change in the electrical impedance signature response through time, which was obtained through surface attached PZT sensors. Concurrently the electrical impedance response was collected through embedded stainless-steel electrodes across the frequency range of 1–10 MHz. This study will act as a guide for selection of a suitable technique for in situ strength gain monitoring using electrical methods

    Electrochemical impedance spectroscopy to monitor the hydration of cementitious materials

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    The electrical properties of Portland cement, and cements containing supplementary cementitious materials (SCM), were obtained over the frequency range 1Hz-10MHz during both the initial 24-hours after gauging with water and up to 1 year. During the initial 24-hours period, the response was measured in terms of conductivity and permittivity with both parameters exhibiting significant temporal changes. It was also evident that whilst the conductivity increased only marginally with increasing frequency of applied electrical field, the permittivity decreased by several orders of magnitude over this range. Moreover, certain features of the permittivity response – which are related to bulk polarization processes – only revealed themselves in the higher frequency range (100kHz-1MHz), and went undetected at lower frequencies. The detailed frequency- and time- domain measurements allowed identification of several stages in the early hydration of cement-based materials and the response can be interpreted in terms of hydration kinetics, physico-chemical processes and microstructural development. It is shown that the methodology can be equally applied to cement-pastes and concretes. In the hardening stage, the conductivity response showed a clear influence of the SCM type, the age of the samples and the used water binder ratio (w/b) in the mixes. The pore solution conductivity has been shown to have a significant effect on the conductivity values particularly at the high replaced mixes. The electrical permittivity showed two different polarization signals depending on the frequency range used, as at frequencies in the range of 100kHz-1MHz, the permittivity response is more related to the samples electrical conductivity, however at higher frequencies (1MHz-10MHz) the permittivity is influenced more by the SCM type and the replacement level in the mixes when w/b is constant. The durability ranking which was obtained from the non-steady-state migration coefficient and the electrical conductivity, showed a strong linear relationship which is in contrast to the relationship between the ranking obtained from the formation factor. This would suggest that both the non-steady-state migration coefficient and the conductivity are affected by the pore solution conductivity of the mixes which, consequently, would give a false indication with regard to the real ranking of the mixes

    Insights into the piezoceramic electromechanical impedance response for monitoring cement mortars during water saturation curing

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    Lead Zirconate Titanate (PZT) based electromechanical impedance (EMI) sensors were used to monitor the mechanical properties development of different water to cement ratios (w/c) cementitious mortar mixes, during the first 28 days of curing under water. Through using the analytical procedure proposed in this study to analyse the EMI data, the different mixes mechanical properties development through the curing period were detected, and the EMI response was able to provide a more detailed interpretation regarding the difference between the surface and the bulk material mechanical properties development. Both the peaks from the impedance signature (Z) and the first difference of the impedance signature (dZ) showed shifts to higher frequency ranges as the age of the samples increased, indicating an increase in the material stiffness. Furthermore, the compressive and the flexural stresses showed an R2 &gt; 0.8 and &gt; 0.9, respectively in relation to the frequency shifts. The relationship between the PZT-EMI response through the curing period and the sample’s mechanical properties was shown to be frequency-dependent; hence a numerical analysis using ANSYS Workbench 18.1 was undertaken to understand this frequency-dependence phenomenon. From the numerical model, the impedance signature response at higher frequency ranges was shown to be dominated by the response from the surface of the hosting material, whereas the response from the specimen's interior dominated the lower frequencies EMI response. The analytical approach proposed in this study is expected to assist in differentiating between internal cementitious materials processes, such as internal curing, and those originating at the surface, such as aggressive chemical agents’ penetratio

    Sensing of damage and repair of cement mortar using electromechanical impedance

    Get PDF
    Lead zirconium titanate (PZT) has recently emerged as a low-cost material for non-destructive monitoring for civil structures. Despite the numerous studies employing PZT transducers for structural health monitoring, no studies have assessed the effects of both damage and repair on the electromechanical impedance response in cementitious materials. To this end, this study was conducted to assess the effects of the damage and repair of mortar samples on the electromechanical response of a surface-mounted PZT transducer. When damage was introduced to the specimen in stages, the resonance frequencies of the admittance signature were shifted to lower frequencies as the damage increased, and an increase in the peak amplitude was detected, indicating an increase in the damping and a reduction in the material stiffness properties. Also, increasing the damage in the material has been shown to decrease the sensitivity of the PZT to further damage. During the repair process, a noticeable difference between the after-damage and the after-repair admittance signatures was noted. The root-mean-square deviation (RMSD) showed a decreasing trend during the repair process, when compared to the before repair RMSD response which indicated a partial recovery for the material properties by decreasing the damping property in the material

    Insights into the piezoceramic electromechanical impedance response for monitoring cement mortars during water saturation curing

    Get PDF
    Lead Zirconate Titanate (PZT) based electromechanical impedance (EMI) sensors were used to monitor the mechanical properties development of different water to cement ratios (w/c) cementitious mortar mixes, during the first 28 days of curing under water. Through using the analytical procedure proposed in this study to analyse the EMI data, the different mixes mechanical properties development through the curing period were detected, and the EMI response was able to provide a more detailed interpretation regarding the difference between the surface and the bulk material mechanical properties development. Both the peaks from the impedance signature (Z) and the first difference of the impedance signature (dZ) showed shifts to higher frequency ranges as the age of the samples increased, indicating an increase in the material stiffness. Furthermore, the compressive and the flexural stresses showed an R2 &gt; 0.8 and &gt; 0.9, respectively in relation to the frequency shifts. The relationship between the PZT-EMI response through the curing period and the sample’s mechanical properties was shown to be frequency-dependent; hence a numerical analysis using ANSYS Workbench 18.1 was undertaken to understand this frequency-dependence phenomenon. From the numerical model, the impedance signature response at higher frequency ranges was shown to be dominated by the response from the surface of the hosting material, whereas the response from the specimen's interior dominated the lower frequencies EMI response. The analytical approach proposed in this study is expected to assist in differentiating between internal cementitious materials processes, such as internal curing, and those originating at the surface, such as aggressive chemical agents’ penetratio
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