Research On Dynamic Properties Andmechanism Of Carbon Nanotubes Cement-based Composite Materials

As a kind of nano material with excellent mechanical properties, carbon nanotubes is suitable to enhance the performance of composite materials in theory. At present, the academia has made significant achievements in the study of the static mechanical properties of carbon nanotubes cement-based composite materials, but research on the dynamic performance of carbon nanotubes cement-based composite materials is still in the exploratory stage. This paper tries to study the dynamic performance of carbon nanotubes cement-based composite materials systematically and explore its action mechanism. Firstly, experimental study on the dynamic performance of carbon nanotubes cementbased composite materials was carried, the effect of carbon nanotubes on the dynamic performance of the composite materials was obtained; Secondly, mechanism analysis on carbon nanotubes cement-based composite materials was done with the experimental methods of SEM, hydration heat, XRD, TG-DSC and AC impedance spectrum. Main research contents of this thesis are as follows:The effect of mixing amount of carbon nanotubes on the dynamic performance of cement-based composite materials was studied with the method of mechanical strength test, damping test, fracture toughness test and dynamic thermal analysis test. Results show that carbon nanotubes can improve the flexural strength, fracture toughness, crack-mouth opening displacement, loss factor of composite material and first-order damping ratio of structure in varying degrees, and the compressive strength and storage modulus of composites decreased.In order to provide the theoretical basis for the improvement of composite materials dynamic performance, a microcosmic test on carbon nanotubes cement-based composite materials was carried with SEM test, hydration heat test, XRD test and TG-DSC test. The results show that the increase of flexural strength, fracture toughness, crack-mouth opening displacement, loss factor of composite material and first-order damping ratio of the member are mainly attributed to the energy consumption of carbon nanotubes, including the carbon nanotubes bridging effect, breaking off effect, pulling out effect and changing cracks development. While the decrease of compressive strength and storage modulus is mainly attributed to the inhibition of the cement hydration reaction during carbon nanotubes re-aggregate which reduces the hydration product and forms matrix defects which can lead to stress concentration phenomenon.Electrochemical impedance spectroscopy(EIS) was employed to study the the effect of carbon nanotubes on hydration reaction of cement and electric conductivity of cement-based composite materials.The results show that carbon nanotubes inhibit the hydration reaction of cement and make the internal charge transfer resistance of cement-based composite decrease. Decrease of composite charge transfer resistance is mainly attributed to that carbon nanotubes increase the conductive ions content of pore solution and pore water ratio. Another reason is that good conductive property MWCNT fo rms a short circuit in the matrix material, thereby reducing the resistance of the composite. Therefore, it can be seen from the EIS analysis that carbon nanotubes inhibit the hydration reaction of cement and improve the water retention property of composites, this is identical with the result of microcosmic test.