Prepration And Smart Properties Of Carbon Fiber/Sulphoaluminate Cement Composites

The health monitoring of structures in civil engineering requires embedding the all kinds of sensor in its key position. The carbon fiber reinforced cement composite (CFSC) has excellent smart properties. The sensor made by the carbon fiber reinforced cement is suitable to the application in civil engineering fields. CFSC has good compatibility with concrete. Therefore, research and development of the carbon fiber reinforced cement play an extremely important role in advancing all kinds of civil engineering structure to be intelligent. The carbon fiber/sulphoaluminate cement composite (CFSC) is prepared when the cement matrix is sulphoaluminate. The dispersion technology of carbon fiber is studied. The piezo-resistivity, piezo-capacitivity, temperature-resistivity and temperature-capacitivity effects are studied and the influences of surrounding and hydration age on the smart properties of CFSC are discussed. The following conclusions and innovation can be obtained.The effects of concentration of dispersant, mixed technology and fly ash on the dispersion of carbon fiber are studied. The dispersion degree of carbon fiber has the maximum value with the constration of dispersant rising. The dispersion degree of carbon fiber is good when the concentration of methylcellulose is 0.051 g/mL. And the first mixed method is used in the mixed technology. The dispersion degree is improved with fly ash.The influences of carbon fiber content on the piezo-resistivity and piezo-capacitivity effects of paste, mortar and concrete of CFSC are analyzied. The influences of nano-TiO₂, carbon nanotube, fly ash and oxided carbon fiber treatment on the piezo-resistivity and piezo-capacitivity effects of CFSC are studied. The chang extents of the piezo-resistivity and piezo-capacitivity effects of the paste, mortar and concrete of CFSC have the maximum value with carbon fiber content rising. The paste, mortar and concrete of CFSC possess good piezo-resistivity and piezo-capacitivity effect when CFSC contains 0.5% carbon fiber content. However, the extents of piezo-resistivity and piezo-capacitivity effects decrease in turn when the carbon fiber content is the same. 6% nano-TiO₂ can improve the piezo-resistivity effect of CFSC, but the flexural strength decreased when Nano-TiO₂ is superfluous. The change extent of the piezo-resistivity effect of CSFC gains the maximum value when carbon nanoruber content is 0.6%, and the change extent of the piezo-capacitivity effect of CFSC gains the maximum value when carbon nanotube content is 0.4%. The piezo-resistivity and piezo-capacitivity effects of CSFC are improved when 10% fly ash is added, and carbon fiber is oxidized by nitric acid. The piezo-resistivity effect is improved and the piezo-capacitivity effect of CFSC decreased when carbon fiber is oxidized by nitric acid. The carbon nanotube has the superiority to improve the piezo-reisitivity and piezo-capacitivity effects.The effects of carbon fiber, nano-TiO₂ and carbon nanotube content on the temperature-resistivity and temperature capacitivity effects of CFSC are discussed. CFSC possess good temperature-resistivity and temperature-capacitivity effects when the carbon fiber content is 0.5% and temperature is in the range of -40℃and 86.7℃. The resistivity of CFSC is stable in thermal holding process when temperature is 50℃or 70℃. The curve of the temperature-resistivity effect is unchanged in the thermal circle. The influence of nano-TiO₂ particles on the temperature-resistivity effect of CFSC is small. 0.4% carbon nanotube can improve dramatically the linear change of the temperature-resistivity effect. CFSC possesses good temperature-capacitivity effect. When the carbon fiber content is 0.5%, the temperature-capacitivity effect of CFSC is stable, and this characteristic is sable at fixed temperature of 70℃for a long time. The shape curve of the temperature-capacitivity effect is stable in thermal circle. Carbon nanotube can improve dramatically the linear change of the temperature-capacitivity effect. Therefore, CFSC mixed by carbon nanotube can be developed into temperature sensor to sensen temperature based on its temperature-resistivity and temperature-capacitivity effecs.The influences of pressing pressure on the smart properties of CFSC are studied. Whenthe circle load is the same, the change extents of piezo-resistivity and piezo-capacitivity effects of CFSC prepared by pressing technology are smaller than the CFSC's prepared by casting technology. When the pressing pressure is 7MPa or 10MPa, CFSC possesses excellent piezo- resistivity effect (the carbon fiber content is 0.5%). This is related to the porosity of CFSC. The temperature-resistivity and temperature-capacitivity effects of CFSC prepared by pressing technology are similar to the CFSC's prepared by casting technology. And the curves of the temperature-resistivity and temperature-capacitivity effects of CFSC prepared by pressing technology are much stable. Compared to the Arrhenius equation curve of CFSC prepared by casting technology, the Arrhennius equation curve of the temperature-resistivity effect of CFSC prepared by pressing technology is much linear. The change extent of the temperature- resistivity effect decreases with pressing pressure rising. The extent of the temperature- capacitivity effect increases with the pressing pressure rising. The pressing technology can improve the linear change of the smart properties of CFSC. This is benefit to control the measure singal.The effects of surrounding and humidity on the smart properties of CFSC are discussed. The resistivity of CFSC decreases and the capacitivity effect of CFSC increases with the humidity rising. Therefore, the piezo-resistivity effect of CFSC is weakened. The change extent of the piezo-capacitivity effect increases with humidity rising. And when the humidity is higher, the piezo-capacitivity effect becomes stable. The resistivity of CFSC decreases with the hydration age rising. At the same time, the curve of the piezo-resistivity effect becomes much stable and linear. The capacitivity of CFSC increases with the hydration age rising. However, the change trend of the piezo- capacitivity effect of CFSC is similar to its piezo-resistivity effect. The resistivity and capacitivity of CFSC is unstable with hydration age. In order to gain the stable temperature-resistivity and temperature-capacitivity effects curves, the hydration age of CFSC must be enough.By optimizing the processing conditions and composition, and discussing the influencing factors on the smart properties of CFSC, good CFSC with smart properties was obtained. The influencing mechanisms of pressing pressure, surrounding and humidity on the smart properties of CFSC were obtained. Our works will provide some useful information and theory basis for preparing sensor with CFSC. And it will play an extremely important role in advancing all kinds of civil engineering structure to be intelligent.