Epoxy Matrix Composites Filled With Nano-Carbon Black And Their Strain And Crack Monitoring

Structure health monitoring is an attractive topic in civil engineering. It needs sensors with high sensitivity, good stability and durability to carry out health monitoring of civil infrastructure. In this dissertation, according to the requirement of civil engineering, the electrical and electromechanical properties of Carbon Black (CB)/epoxy matrix sensors are systematically researched. The sensors are also embedded in reinforced concrete structure to form self-monitoring system. The main research contents are as follows:First, taking the mean value and variation coefficient of resistivity combined with image of Scanning Electron Microscope (SEM) as the evaluating indicators, the influence of stirring time and surface modification of CB on the dispersion of CB in epoxy matrix which affects the electromechanical properties of CB/epoxy sensor is studied and the basic specimen preparation techniques are obtained accordingly. The influence of different type of electrodes on the electrical and electromechanical properties of sensor is studied by analyzing the difference of electric field formed by different type of electrodes and based on which the best type of electrode is selected.Second, mechanism of the influence of diameter and structure of CB particles on electromechanical properties of sensor is analyzed by comparing the I-V characteristic and electromechanical properties of sensors containing different diameter and structure of CB. The electromechanical properties of epoxy matrix bulk sensor under cyclic loading are studied. The electromechanical properties of CB/epoxy sensor restricted by surrounding carbon fiber under static and cyclic loading are further studied. The way to increase the sensitivity of CB/epoxy matrix sensor is found.Third, the single electrode and multi-electrodes CB/epoxy film sensors are prepared. The influence of CB content on resistivity and electromechanical properties of single electrode film sensors is studied. The percolation characteristic is found in electrical properties of film sensor. The electromechanical properties of film sensors with different type of electrodes are studied. The electromechanical properties of film sensors under cyclic loading are also studied. The reason causing the decrease of sensitivity coefficient of film sensors under cyclic loading is analyzed. Based on the analysis, the monitoring properties of film sensors under cyclic loading are improved by adding the CBs with different diameter and structure. The monitoring properties of multi-electrodes film sensors under bending are studied.Fourth, the basic properties of CB/epoxy sensors such as hysteresis, time zero-drift, full-scale values, sensitivity, linearity and repeatability are studied. The influence of temperature and humidity on the monitoring properties of sensors is also studied and the temperature compensation approach is proposed. The influence of loading velocity on the monitoring properties of sensor is investigated too. Finally, the CB/epoxy sensors are used in concrete column and reinforced concrete beam to form self-monitoring system. The compressive strain of concrete column and compressive region in reinforced concrete beam are monitored by epoxy matrix sensor. The monitoring results of epoxy-based sensor are in compliance with the results tested by displacement meter and strain gauges. Meanwhile the cracks in tensile region of reinforced concrete beam are also monitored by multi-electrodes film sensors. The results show that the self-monitoring system has good performance and high feasibility.