Dissertation > Industrial Technology > Building Science > Building Materials > Non-metallic materials > Concrete and concrete products > General issues

Influence of Service Environments on the Working Performance of Chloride Sensor in Concrete

Author WangCuiCui
Tutor GaoXiaoJian
School Harbin Institute of Technology
Course Materials Science
Keywords chloride sensor concrete structure performance of electrochemistry environmental conditions real-time monitoring
CLC TU528.0
Type Master's thesis
Year 2011
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The inducement of chloride is one of the major elements in the corrosion ofreinforced steel in concrete structures. Therefore, electrochemistry sensor appears as anewly-developed technology which can measure the distribution of chloride ion timelyand accurately in concretes in recent years. However, the structure of the reinforcedconcrete will be affected by different environmental factors in practical projects, and itis likely to influence the working stability of chloride sensor in concretes. Hence, thispaper is based on the electrochemistry-based all-solid-state concrete chloride sensor,which takes Ag/AgCl as the working electrode and MnO2 electrode as referenceelectrode, and has studied the working stability of it in different environment as well asthe electrochemistry performance of the chloride sensor in concretes of different contentof the chloride ion. Thus, it will provide the theoretical evidence for the widerapplication of the technology in projects, and supply the theoretical basis for accuratelyevaluating and predicting the level of the concrete structures which is corroded by thechloride.In this paper, the ability of Nernst response and electrochemistry performance ofthe chloride sensor has been studied systematically in the mortar of different content ofthe chlorate. The results show that, in the mortar of different content of the chloride salt(1%、2%、3%), the linear relationship between the potential output value of the chloridesensor and the logarithm of chloride ion concentration corresponds well with the Nernsttheory. In the mortar of different concentrations of the chloride ion, the sensor has apoor resistance to interference under the polarization of constant current, because thepotential drift of the sensor is very high, and the time of the potential value of the sensorwhich gets back to the initial value is slow in the process of the constant electric currentpolarization test. During the cyclic voltammetry measurement, there is an anodic andcathodic peak in each cyclic voltammograms of the mortar of different concentrations ofthe chloride ion, and the ratios of the current of the anodic and cathodic peak are closeto one, which means, there is an irreversible chemical reaction happening on thechloride sensor during the cyclic voltammetry measurement.The concrete and mortar with different strength as well as different content of thechlorate are designed, and the influence of environmental conditions (such as loading,the cycle of freezing and thawing, sulfate attack, different humidities environment and adjunctive electric field) on the working performance of chloride sensor was stuied inconcrete or mortar. The results show that the working performance of chloride sensorwhich is embedded into concrete is hardly affected when the load changes between therange of 0 and 50% of the compression strength. But when the load reaches to 60% ofthe compression strength or above it, the working performance of chloride sensor isinvalid. In the environment of concrete, the higher the humidity is, the lower thepotential value of chloride sensor becomes, which means the performance of real-timemonitoring of chloride sensor is fine. Under the high-alkaline circumstance of concrete(pH=12.5), the chloride sensor shows favorable detectivity. With the decrease of pHvalue, gradually, the detectivity of chloride sensor becomes bad. After twenty cycles offreezing and thawing, the chloride sensor embedded into concrete displays excellentworking performance. With the cycle of freezing and thawing increasing, however, theperformance of the chloride sensor gets bad.After electrochemical extraction treatment on chloride, it is investigated that in themortar of different content of the chloride salt, the potential value of chloride sensorincreases gradually with the time of electrochemical chloride extraction extends, andthen in the position of the bottom of chloride sensor, which is nearby the reinforcingsteel, the concentration of the chloride ion becomes less and less. And eventually, thefinal values monitored by chloride sensor are highly close to the content of chloride ionin concrete. Consequently, it proves that the chloride sensor can also be used to in situmonitoring of chloride ions during the process of electrochemical extraction treatmenton chloride.

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