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| Study on thermal deformation and astuteness of conductive concrete sensors |
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Abstract Abstract Sensors are widely used in the field of concrete structure health detection. Compared with traditional sensors, cement-based sensors have better compatibility with concrete. However, Addition of conductive dope will change its characteristics. Therefore, it is necessary to study the sensitivity of cement-based sensors in concrete. In this paper, cement-based sensors with different sensitivity are designed. The thermal deformation characteristics and the law of astuteness of the sensor are tested. The feasibility of the sensor being embedded in concrete for structural deformation detection is verified. It is found by experiment that the conductive concrete, which contains carbon nanotubes, possesses thermal expansion - thermal contraction characteristics. Therefore, there is a thermal expansion - thermal contraction transition temperature. When the environment temperature is less than such a transition temperature, the material will undergo expansion with the temperature. However, if the environment temperature is greater than the transition temperature, the material shrinks with the temperature. The experiment proves the transition temperature linearly decreases with content of carbon nanotube. The experiment also indicates that the piezoresistive effect of carbon nanotube could be affected by the concrete dry shrink stress if sensors are embedded in concrete samples. The nucleation and growth of micro-damage lead to an increase in the spacing of conductive fillers, and this could cause an increase in the resistivity of the sensor. Therefore, there is a competition mechanism, namely, compressive load leads to decrease of resistivity of sensors, while damage evolution causes the increase of the resistivity. The piezoresistive effect of sensors has non-linear characteristics due to such a competition mechanism. Based on the experimental results and the tunnel effect theory of electronic leap, the piezoresistive model of cement-based sensor is established. It is believed that the experimental results and theoretical model obtained in this paper have guiding significance for the design of cement-based sensors.
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Received: 30 November 2020
Published: 14 December 2021
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2021, Vol. 42 
