The Dispersion Of Carbon Nanotubes And Effects On Properties Of Cement-based Materials

The outstanding mechanical properties of carbon nanotubes(CNTs)make it a potential candidate for enhancing cement based fibers.However,the CNTs are difficult to disperse uniformly due to the presence of the Vander Waals' force.A lot of studies had been done on the dispersion of carbon nanotubes in composite materials(e.g.,resin based,ceramics).In this paper,the dispersion of carbon nanotubes in cement based materials was studied.Three types of carbon nanotubes assisted dispersion were studied.The main research results were as follows:(1)The effects of mechanical vibration mill and ultrasonic on the dispersion of CNTs in the powder were discussed.The results showed that the average particle size was similar to that of CNTs,which was more favorable for the dispersion of CNTs in the powder.The dispersion of CNTs in powder was poor for the larger particles of fly ash.The length of CNTs in silica fume was reduced but no aggregates by vibration mill.In the fly ash CNTs aggregates were found.CNTs composite powder was mixed into cement paste,the fluidity after the changed not obvious,and the mechanical strength decreased.The aggregates of CNTs were not obvious by ultrasonic dispersion method in powder.When adding CNTs composite powder to the cement,the flow of the paste decreased significantly and the flexural strength of cement matrix increased 10%.(2)The use of graphene oxide(GO)as a dispersant to overcome the agglomeration of carbon nanotubes was discussed.UV Vis spectroscopy and scanning electron microscopy results showed that carbon nanotubes could be dispersed in graphene oxide suspension,and the stability of the hybrid system was very good.Furthermore,the hybrid graphene oxide/carbon nanotubes on the fracture resistance of cement based composite materials have a significant increase.Hybrid graphene oxide/carbon nanotubes(0.02wt%GO and 0.04wt%CNTs)on the compressive strength and flexural strength were increased by 23.9% and 16.7%,respectively.Scanning electron microscope images showed that the hybrid graphene oxide / carbon nanotubes uniformly dispersed in the cement hydration products.In addition,the results of mercury intrusion porosimetry(MIP)showed that the hybrid graphene oxide/carbon nanotubes could improve the pore size of cement matrix.(3)Based on the principle of in-situ synthesis of CNTs,the synthesis parameters of CNTs on fly ash particles were studied,and the synthesized products were characterized.The results showed the effect of synthesis time,catalyst,temperature,air flow rate on yield of CNTs synthesized on the surface of fly ash.The results showed that the yield of CNTs synthesized on fly ash particles was higher at 600?.The defects in CNTs synthesized at 700 degrees were the most.CNTs / fly ash composites exhibited hydrophobicity.When the CNTs/fly ash composites incorporated into cement-based materials,the mechanical properties of cement-based materials decreased and porosity increased,indicating that CNTs on the surface of fly ash affected the interaction between fly ash and cement hydration products.