| Carbon fiber reinforced concrete(CFRC)is a new type of composite material made of carbon fibers in ordinary concrete.CFRC has good mechanical properties,and also has a certain degree of dexterity.With the sensitivity of materials,self detection of building structures can be realized.In recent years,more and more scholars have studied the electrical properties of CFRC.However,because of the difficulty of carbon fiber dispersion,the practical application of carbon fiber reinforced concrete is not extensive.From the point of view of practical application,the short carbon fiber is chosen as the conductive material,and its mechanical and force sensitive properties are studied.Firstly,the research status of carbon fiber reinforced concrete and shaft lining monitoring at home and abroad is reviewed.Then,through the laboratory test,the effects of the processing technology,the dosage of dispersant,the amount of carbon fiber and the length of carbon fiber on the compressive properties and resistivity of CFRC are discussed.Then the resistance of carbon fiber reinforced concrete under different loading conditions is studied.The study of the mechanical properties of CFRC shows that the fabrication process of CFRC has a certain effect on its compressive strength,but the smaller the size of carbon fiber,the less affected.With the increase of carbon fiber content,the strength of concrete decreases and rises and decreases.The optimum content of carbon fiber is 0.6%~1.0% of cement quality.The shear strength of the interface between CFRP and plain concrete is greater than that of ordinary concrete,and the two materials can be used together.Different fabrication processes can effectively reduce the resistivity of concrete,and the resistivity decreases with the increase of carbon fiber content.Under normal conditions,the resistance of CFRC is generally stable,and it will be affected by polarization,which will increase by about 2%.The CFRC has a good negative temperature coefficient(NTC)effect,that is,the temperature rises,the resistance of concrete decreases,the temperature decreases,and the resistance of concrete increases.The CFRC has good force sensing properties,and the resistance of concrete is approximately linearly reduced even when loading uniformly.Under cyclic loading,when the stress level is low,the magnitude of each cycle resistance is basically the same.After unloading,the resistance value basically revert to the initial state.When the stress level is high,the resistance value is higherthan the initial value after unloading,and the resistance increases with the increase of cycle times.Under the same stress level,the magnitude of resistance change is directly proportional to the carbon fiber content.Using the material sensitivity,CFRC can be used to monitor the safety of the wellbore.By comparing with the traditional vibrating wire sensor data,the change of the resistance value of the shaft wall can be used to reflect the change of the stress of the shaft wall.Considering the factors of strength,force sensitivity and field implementation,carbon fiber with 0.1mm length is used to make CFRC with 0.6% content,and a high3.6m and diameter 5.5m smart wall of carbon fiber concrete is built at the-618 m of shaft shaft,and the circular electrode arrangement is used to monitor the safety of the wellbore.and it is arranged by ring electrode to monitor the safety of well wall.The monitoring results show that the resistance change of CFRC can reflect the change of the stress of the wall well.By linear fitting,the quantitative relationship between the resistance change and the strain is found.The result is in agreement with the traditional vibrating wire sensor monitoring data.The strain of each electrode is calculated back,and the distribution of strain along the shaft wall is given,so that the borehole wall can be monitored in an all-round way,thus laying the foundation for the realization of intelligent wellbore in the future. |
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