The Mechanical-electrical-smart Properties Of Conductive Cement Based Materials

Building projects are constantly degraded by service induced damage under external loading and result in the decrease of bearing capacity.According to this issue,the real-time monitoring of damage in concrete structure might have a significant value in practice.Traditional monitoring methods such as built-in sensors exhibit disadvantages of high cost,poor durability and environmental restrictions which hinder the application of these methods.Conductive cement based material is a functional material which is doped with conductive components.Whereas,the well-dispersed conductive component is able to form electric conduction network in the matrix and subsequently possesses the facility to self-sensing of its deformation and damage in concrete,thereby offering new potentials for real time monitoring of internal damage and use statement in concrete structure.The mechanical,smart properties and electrical conductivity of cement based materials were investigated in this paper and research contents and conclusions are as follows:The effects of different functional materials on the electrical conductivity of paste and mortar were studied.The resistivity of paste decreased with the increase of functional materials content.The percolation threshold of carbon fiber in paste is about 1%,the value rises up to 10% for graphite in paste.The 28 d resistivity of paste decreased and then increased,then decreased and then increased with the increase of substitution ratio when carbon fiber was partially replaced by graphite.The resistivity of conductive paste modified with polymer increased with the increase of polymer-cement ratio while the mechanical property shown the opposite trend;The optimal substitution ratio of carbon fiber was 25% and the optimal polymer-cement ratio of modified conductive mortar was 0.02.The smart properties of carbon fiber-graphite concrete were studied.The resistivity of specimen experienced the descent stage,balance stage and surge stage during the process of according to compression stress,which indicated that defects or cracks were compacted then new defects and cracks appeared finally the specimen broken.The addition of polymer prolonged the balance stage since the polymer effectively restrain the crack development;The resistivity decreased during loading and increased after unloading when the specimens were under cyclic loading.The variation of each cycle are basically the same;Conductive concrete with 0.75% of carbon fiber and 2.5% of graphite exhibited the most excellent performance in smart property under flexure while the resistance change rate reached a maximum of 8.60%.Temperature distribution of conductive concrete slab was analyzed by ANSYS.The result shown that temperature decreased from the center position to the surrounding position,the highest temperature in the center position reached 47.36? while the lowest temperature in the four corners reached 41.72?;The experiments shown the similar result with the simulation conducted by ANSYS and indicated the correctness of this method;The variation in deformation and strain of conductive concrete during the process of heating were also analyzed.The deformation of the specimen increased from the center position to the surrounding position,the maximum deformation of 0.13 mm appeared in the four corners of specimen,and the minimum deformation of 0.89×10-3 mm appeared in the center of the upper surface.