Study On Self-sensing Nickel Powder Cement-based Composites And Their Application

Owing to such advantages as high sensitivity, excellent compatibility with concrete,good durability, nickel powder cement-based composites have widely potentialapplication in the field of structural health monitoring and traffic detection. Focusing ontwo themes of nickel powder cement-based composites and their application, sensingmechanism of nickel powder cement-based composites and their sensing characteristicmodel, the numerical simulation of the mechanical properties of nickel powdercement-based sensors embedded in concrete and their production parameters, thenumerical simulation of the coordination degree of sensors when they are embedded inconcrete member, and the traffic detection based on nickel powder cement-basedcomposites are studied in this paper. The main works of this paper are as follows:(1) Comparing the electrical and sensing properties of cement-based compositeswith the spherical and the spiky spherical nickel powder, their differences result fromthe different surface morphologies of nickel particles. The composites with spikyspherical nickel powder display non-linear current density-electric field characteristics.This phenomenon confirms that the sensing mechanism of composites with spikyspherical nickel powder is the field emission effect. The sensing characteristic model ofspiky nickel powder cement-based composites is established based on the field emissioneffect. A third-order polynomial model can be well used to describe the relationshipbetween the resistivity and the compressive stress/strain.(2) The mechanical properties of nickel powder cement-based sensors embedded inconcrete are analyzed by ANSYS. The stress of sensors is non uniform and there islarger difference of stress between sensors and surrounding concrete. However, thestrain of sensors is approximately equal to that of surrounding concrete. According tothe strain coordination degree between the sensors and concrete, the suitable size ofsensors is20×40×20mm, and the appropriate voltage electrode spacing is5mm.Furthermore, the surface of the sensors should be as rough as possible.(3) The strain coordination degree between the sensors and concrete when sensorsare embedded in concrete member is analyzed by ANSYS. The buried position ofsensors, the skew angle of sensors, the strength grade of concrete, the magnitude of loadand the load type all have some influence on the strain coordination degree. Themonitoring results should be amended in order to monitor the strain of concrete.(4) The nickel powder cement-based sensors are embedded into a concretepavement to set up a self-sensing pavement for vehicle detection. The result of vehicledetection confirms that the nickel powder cement-based sensors are feasible for vehicledetection. The structure of the self-sensing pavement is optimized to achieve the vehicleflow and speed detection. The mechanical properties of nickel powder cement-based sensors embedded in concrete pavement are analyzed by ANSYS. The concrete aroundthe sensors has strong restriction on them. This will not affect the traffic flow and speeddetection, but has great effect on the vehicle weight detection.