Study On Mechanical Properties And Freezing Resistance Of Cement-based Materials With Different Diameters Of Carbon Nanotubes

Carbon nanotubes have good mechanical properties and chemical stability,and can play a significant role in bridging,filling and nucleation when they are mixed into cement,thus effectively optimizing the structure of interface transition zone.However,the large aspect ratio and Van der Waals force between the pipes make the pipes entangled or agglomerated.Effective dispersion is needed before they are applied in cement-based materials.At present,the research mainly focuses on the influence of single carbon nanotubes on the properties of cement-based materials,while the research on the influence of different diameter carbon nanotubes on the mechanical properties and frost resistance of cement-based materials is still less.Therefore,the effects of carbon nanotubes with different diameters on mechanical properties and frost resistance of cement-based materials were studied,and their microstructures were analyzed in this paper.The main work is as follows:(1)Dispersion effect of carbon nanotubes.Surfactant,magnetic stirring and ultrasonic dispersion were combined to disperse carbon nanotubes,and the optimal ultrasonic dispersion parameters were determined through experiments.The mechanical properties of carbon nanotubes cement-based samples prepared under different dispersion time and strength were tested.The dispersion effect of carbon nanotubes was evaluated by improving the mechanical properties.It was found that the dispersion effect of carbon nanotubes was the best when the ultrasonic dispersion time was 60 min and the ultrasonic intensity was 1050 W.(2)The effect of carbon nanotubes on the mechanical properties of cement-based materials.The mechanical properties of carbon nanotubes cement-based specimens were tested at 7 and 28 days of age.It was found that the compressive strength and flexural strength of carbon nanotubes increased most obviously when the carbon nanotubes content was 0.1wt% and 0.2wt%,respectively.Carbon nanotubes with diameters of 10-20 nm had the best effect on the compressive strength of cement-based materials,while carbon nanotubes with diameters of 40-60 nm had the best effect on the flexural strength of cement-based materials.Comprehensive thermal analysis results show that the addition of carbon nanotubes can promote cement hydration and improve the performance of cement-based materials.It was found by SEM that carbon nanotubes had the effect of bridging,pulling out and nucleating.The larger the diameter of carbon nanotubes,the better the dispersion effect.(3)The influence of carbon nanotubes on the frost resistance of cement-based materials.The effect of carbon nanotubes on the frost resistance of cement-based materials was studied through the mass loss rate,relative dynamic modulus and strength variation of carbon nanotubes cement-based samples under different freeze-thaw cycles.It is found that the addition of carbon nanotubes can effectively improve the freeze resistance of cement-based materials.The addition of 0.1wt% carbon nanotubes can improve the freeze resistance of cement-based materials.The frost resistance of cement-based materials can be improved better when the content of carbon nanotubes is 0.1wt% and their diameter is 10-20 nm.(4)The effect of carbon nanotubes on the pore structure of cement-based materials.The pore structure of carbon nanotubes was tested by mercury porosimeter,and the effect of different diameter carbon nanotubes on the pore structure of cement-based samples and the pore structure of samples during freeze-thaw cycles was studied.It is found that the addition of carbon nanotubes can effectively improve the pore size distribution of cement-based materials,and effectively restrain the increase of porosity and the formation of harmful pore in the freeze-thaw cycle of cement-based materials.