Abstract
Commonly used humidity sensors are based on metal oxides, polymers or carbon. Their sensing accuracy often deteriorates with time, especially when exposed to higher temperatures or very high humidity. An alternative solution based on the utilization of Portland cement-based mortars containing in-situ grown carbon nanofibers (CNFs) was evaluated in this study. The relationship between the electrical resistivity, CNF content and humidity were determined. The highest sensitivity was observed for samples containing 10 wt.% of the nanomodified cement which corresponded to 0.27 wt.% of CNFs. The highest calculated sensitivity was approximately 0.01024 per 1% change in relative humidity (RH). The measured electrical resistivity is a linear function of the RH in the humidity range between 11 and 97%. The percolation threshold value was estimated to be at around 7 wt.% of the nanomodified cement, corresponding to ~ 0.19 wt.% of CNFs.
Highlights
Used humidity sensors are based on metal oxides, polymers or carbon
Test sensors were produced as mortar beams composed of a mixture of an ordinary Portland cement (OPC) type CEM I 42.5 provided by Cementa-Sweden and the so-called SmartCem
The study aimed to determine the sensitivity of novel sensors to variations in the humidity. These humidity sensors are based on mortars containing various amounts of the nanomodified Portland cement (SmartCem)
Summary
Used humidity sensors are based on metal oxides, polymers or carbon. Their sensing accuracy often deteriorates with time, especially when exposed to higher temperatures or very high humidity. Sensors based on matrixes containing Portland cement measure changes of r esistivity[14] In this case, the measured changes were related to alterations of the pore structure leading to either shrinkage or expansion of the matrix, water absorption or desorption hysteresis at the interface. The measured changes were related to alterations of the pore structure leading to either shrinkage or expansion of the matrix, water absorption or desorption hysteresis at the interface Humidity sensing of such matrixes depends on the amount of the incorporated conductive material like carbon fibers (CFs). The humidity sensing is based on an interaction of water molecules with the sensitive core layer This results in a change of the effective refractive index of the fiber core and in a shift of the Bragg w avelength[22]. The results showed that an increasing amount of CNTs/CNFs tends to worsen the fresh mix workability
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