The purpose of the diploma thesis was to design and test the functioning of a sensor system, which could be used for long term measurements of the temperature and relative humidity in mineral binder composites. In a cooperation with the Faculty of Electrical Engineering University of Ljubljana, we have developed a fairly simple measuring system consisting of 8 sensors for measuring temperature and relative humidity, a system for receiving and processing signals, a power supply system and data transmission system.
In the first part of the thesis we assembled the sensors and checked if they are working properly. We decided to use Sensirion sensor probes, named SHT 25. These sensors are using a digital I2C interface and are offering long-term stability, commercial accessibility and acceptable measurement errors. The environment in which the sensors will be integrated is very aggressive, so sensors have been protected with a special filter cover and epoxy coating all over the sensors. All the values sensors recorded were stored on a Raspberry Pi3 computer unit. All the sensor data readings and recordings works on the basis of three written programs, which are executed every 2 minutes. To compare all the received values with SHT sensor system we used commercially well known sensor system Ahlborn ALMEMO.
In the second part of the thesis we prepared three different mixtures: pure lime mortar, cement – lime mortar and lightweight self – compacting concrete. We also prepared 8 brick units. All the mixtures were mixed by standard procedure and the sensors were installed inside them.
All the obtained values of temperature and relative humidity of both sensor system were analysed and compared with each other. We discussed the hydration process and its theoretical background in more details. By comparing all the obtained results we found that despite satisfying performance, the sensor system needs some improvements. Worse performance were observed when comparing relative humidity results. Within investigation we identified which changes and improvements are needed or can be done within the measurement system development.
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