| Smart concrete has both structural and functional properties,and has the potential of self-monitoring of concrete structure.At the same time,single-phase conductive smart concrete has the problems of low mechanical properties,high preparation cost and poor resistance stability.In this paper,carbon fiber and graphite are used as conductive materials.The strength,conductivity and pressure sensitivity of composite conductive smart concrete are studied.Finally,the electrical resistance tomography of smart concrete is preliminarily studied by simulation method.The experimental results show that increasing the length of carbon fibers and the mesh number of graphite is more conducive to the preparation of smart concrete with high strength and good electrical conductivity.Graphite,silica fume and water cement ratio significantly affect the strength of smart concrete,while carbon fibers have a relatively small impact.Adding carbon fibers or graphite alone can significantly reduce the resistance of concrete.The percolation threshold of carbon fibers is about 0.2%~0.6%.Graphite has no obvious percolation phenomenon.When the content of carbon fibers reaches the percolation threshold,adding a certain amount of graphite can further reduce the resistance of concrete.Adding silica fume and increasing watercement ratio can reduce the resistance of multiphase conductive smart concrete,but the influence of both is small.The resistance of smart concrete tends to be stable at 28 days of age.The resistance of smart concrete under natural curing is about twice as high as that under standard curing.The resistance of smart concrete is greatly affected by temperature.With the increase of temperature,the resistance value of smart concrete decreases.Environmental humidity has little effect on the resistance of smart concrete,but the moisture content of smart concrete itself will affect its resistance.The higher the moisture content,the smaller the resistance.When the loading direction is perpendicular to the direction of the test electrode sheet,the measured pressure sensitivity is more remarkable.The influence of loading rate on the pressure sensitivity is less.When loading is faster,the pressure sensitivity is slightly enhanced.The resistance of the smart concrete remains basically unchanged under constant load.The resistance of the composite conductive smart concrete can be divided into four stages during the whole process of loading to failure.Rapid descent stage,slow descent stage,almost invariable stage and rapid ascent stage.The pressure sensitivity of smart concrete under cyclic loading has good repeatability.In the test range,increasing the content of carbon fiber and graphite can help to improve the pressure sensitivity of smart concrete.Comsol software can be used to simulate the forward problem of smart concrete resistance tomography.The results show that the boundary shape of the field has a great influence on the minimum and dynamic range of the measured voltage.The change of resistance caused by compression and cracking of smart concrete can cause the regular change of the measured voltage at the boundary.The boundary voltage signal can respond to the size,position,shape of the compressed area,the length,position and angle of the crack,but it is insensitive to the width of the crack.The linear back projection algorithm program and conjugate gradient algorithm program are compiled.According to the data obtained from forward simulation,the imaging simulation of compression and crack of smart concrete is carried out.The results show that the linear back projection algorithm has high efficiency and poor accuracy,and the conjugate gradient algorithm has good imaging effect.The imaging simulation of single point seepage and uneven strain distribution of the shaft lining is carried out using the shaft lining as the prototype.The results show that ERT has a certain application prospect in the field monitoring of Smart Concrete. |
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