Study On Mechanical Properties Of Carbon Nanotubes Sulphoaluminate Cement Composites

Sulphoaluminate cement is widely used in pavement and bridge repair and reinforcement,marine engineering and other engineering fields due to its fast setting,early strength,corrosion resistance and many other advantages.However,the late strength of the cement is low and brittle,so nano materials can be used to improve the mechanical properties of sulphoaluminate cement.In this paper,polyvinylpyrrolidone and polycarboxylate superplasticizer were used to disperse carbon nanotubes and prepare carbon nanotubes sulphoaluminate cement composites.The modification effect of carbon nanotubes on sulphoaluminate cement was studied.The micro mechanism of carbon nanotubes on improving the mechanical properties of sulphoaluminate cement composites was studied by nano indentation test and molecular dynamics simulation.The main conclusions are as follows.(1)Polyvinylpyrrolidone(pvpk30)was used as dispersant to disperse carbon nanotubes.The effects of dispersant concentration and ultrasonic time on the dispersion of carbon nanotubes were studied.It was found that when the ratio of dispersant concentration to multi walled carbon nanotubes concentration was 1:4 and ultrasonic time was 1 h,the dispersion and stability of carbon nanotubes were the best.(2)Carbon nanotubes sulphoaluminate cement composite blocks with different water cement ratio were prepared,and the compressive and flexural tests were carried out after 28 curing.The results show that when the water cement ratio is 0.25 and the content of carbon nanotubes is 0.04%,the compressive and flexural strength of sulphoaluminate cement blocks reach the highest,which are 113.3MPa and 24.6MPa respectively,increasing by 21.4% and41.7% compared with the samples without carbon nanotubes The compressive and flexural strength of carbon nanotubes sulphoaluminate cement composites with water cement ratio of0.40 were the lowest,92.4MPa and 11.4MPa respectively.(3)The elastic modulus and hardness of carbon nanotube sulphoaluminate cement composites were tested by nano indentation tester.The results show that with the increase of carbon nanotube concentration,the average elastic modulus and hardness first increase and then decrease.When the content of carbon nanotube is 0.04%,the average elastic modulus and hardness reach the maximum,which are 37.977 GPa and 1.836 GPa,respectively 4% and12.4% respectively.(4)Molecular dynamics software was used to model and calculate ettringite crystal,the main hydration product of carbon nanotube sulphoaluminate cement composite,and carbon nanotube/ettringite crystal.The results show that the elastic modulus and Poisson’s ratio of 1a×1b×1c ettringite unit cell are 60.18 GPa and 0.32 respectively;the elastic modulus and Poisson’s ratio of 2a×2b×2c ettringite supercell are 59.05 GPa and 0.32 respectively;3a×3b×3c The elastic modulus and Poisson’s ratio of 3C ettringite supercell are 59.20 GPa and0.32,respectively.The elastic modulus and Poisson’s ratio of ettringite unit cell with different sizes are similar.The elastic modulus of CNT/ettringite composite is 74.08 GPa and Poisson’s ratio is 0.32.