Durability Of Injection Grouts Modified By Multi-Walled Carbon Nanotubes Under Sulfate Attack And Drying-Wetting Cycles

This study mainly concentrated on the performance of Carbon nanotubes that can play a significant role in bridging,filling,and nucleation when they are mixed into ultra-fine cement grout materials,thus effectively optimizing the structure of the interface transition zone.However,the large Carbon nanotubes content ratio and Van der Waals force between the pipes make them entangled or agglomerated.Effective dispersion method is needed before they are incorporated into cement-based materials.This research is conducted to investigate the influence of well-dispersed carbon nanotubes on the properties of cementbased grouting materials.Since a research on the influence of carbon nanotubes on the mechanical properties and sulfate attack resistance of cement-based grouts is still not studied yet.Therefore,the effects of carbon nanotubes with different dosages on mechanical properties and wetting-drying cycles’ resistance of cement-based grouts were investigated in this study.The microstructure properties were evaluated and analyzed as well in this research.The main work of the study 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 times and strengths were tested.The dispersion effect of carbon nanotubes was evaluated by improving both the mechanical and microstructural 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 content on the mechanical properties of cement-based grout materials were investigated.The specimens were tested after 7 and 28 days of age.The results showed 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 with a diameter of 10-20 nm.(3)The influence of carbon nanotubes on wetting-drying cycles and sulfate attack resistance of cement-based grout materials was studied through visual appearance test,the mass-loss rate,and the compressive strength loss under different drying wetting cycles.It was found that carbon nanotubes can effectively improve the resistance of cement-based grout materials and with 0.1wt% of carbon nanotubes content,the resistance improvement of cement-based grouts was most obvious.(4)The pore structure and microstructural properties of carbon nanotubes grout materials were tested by SEM,MIP,and Thermal analysis.The effect of different dosages of carbon nanotubes on the pore structure of cement-based samples and the pore structure of the samples under different cycles was studied.It was 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 during the wet-dry cycles of cement-based grouting materials.Thermal analysis results showed that the CNTs can promote the cement hydration and improve the performance of cement-based grouting materials.Through the SEM test analysis,it was found that carbon nanotubes had a perfect effect of bridging,pulling out,and nucleating roles within the cement matrix.