Study On Conductive Theory Of Carbon Fiber Alkali-activated Materials And Preparation Of Sensor

Large structures and infrastructure need to serve for decades or even hundreds of years,in the long-term load of concrete structure will continue to produce damage.When the cumulative damage of concrete exceeds its limit capacity,it will cause great threat to the safety of people’s life and property,so it is very important to monitor the structure health.Sensing element is the hardware foundation of structural health monitoring,high cost,poor durability of existing sensors and the poor compatibility with concrete structure,the induction of concrete is a kind of set in the integration of intelligent materials,structures and sensing can sense its own stress/strain/internal injury has high sensitivity,good durability,high compatibility with concrete structure,etc.Alkali-activated material has free alkali ion migration in conductivity has the advantages of natural alkali-activated conductive material good electrical performance for sensor research provides the basis of favorable conditions,but for alkali-activated material research at present is mainly as a green alternative materials of ordinary cement concrete.However,there are few researches on alkali-activated piezoresistivity sensors.In this research,such as slag,fly ash as raw materials,the use of carbon fiber as the conductive phase,after research the alkali-activated mortar and add carbon fiber conductive,piezoresistivity performance,respectively from the macro and micro perspective to explore the conductive mechanism of piezoresistivity,on the basis of the composite mortar was prepared by alkali-activated sensors,sensor as the feasibility of the concrete cube to study the structure of the monitoring.The main conclusions of this research are as follows:（1）After the addition of conductive carbon fiber,the electrical conductivity of each sample is significantly improved.The SL70 system with better electrical conductivity is more stable and the strain sensitivity is higher,reaching 301.33.Under different sodium oxide content,the Na₂O 4 system has better conductivity,higher pressure sensitive stability and better sensitivity.The electrical properties of Si O₂6 system are the best under different silica content.（2）Ionic conductivity is dominant in the system without carbon fiber.After the carbon fiber is added into the system,under the condition that the bond between the matrix material and the carbon fiber is good,the drying treatment can evaporate the water film on the fiber surface,thus improving its electrical conductivity.（3）The effect of pore structure on conductive materials is great,but the effect of pore size less than 2nm is not obvious.The bond between carbon fiber and matrix and the dispersion in matrix are the most important factors affecting the electrical properties of alkali-activated conductive materials.In the system with higher slag content,the bond between carbon fiber and matrix is better,and the dispersion degree is more uniform,so the conductivity and piezoresistivity are better.Under different silica content,carbon fiber in Si O₂6 system has more perfect lap,so its electrical properties are better than those of the system with lower silica content.（4）The larger sensor size is,the better the carbon fiber conductive path can be built,which can make the sensor have better electrical conductivity and sensitivity.The higher the sand rate is,the smaller the sand particle size is,the greater influence on the working performance of the sensor.（5）The larger sensor is able to share more of the stress of the concrete and therefore give more accurate piezoresistivity results.The alkali-activated sensor can effectively reflect the crack development and stress redistribution process of concrete samples during the process from pressure to failure,and achieve the purpose of structural health monitoring.