Study On Sulphate-corrosion Resistance And Freeze Resistance Of Carbon Nanofibres Reinforced Cement-based Composites

Carbon Nanofibers(CNFs)are novel nano-scale carbon fibers with high strength,high aspect proportion and high Young’s modulus,which are applied widely.In recent years,the research on the properties of nano-materials reinforced cement-based materials has been a hot topic.The mechanical,conductive,thermal and deformation properties of nanomaterials reinforced cement-based materials are studied,and the mechanism of function is analyzed and discussed.The purpose of this paper was to study the dispersion properties of CNFs in water and cement granular systems,the physical properties,mechanical properties,sulfate-corrosion resistance and freezing resistance of CNFs reinforced cement-based composites.In this paper,the dispersion property of CNFs in aqueous solution was studied by means of ultraviolet-visible absorption spectroscopy(UV-vis),static and centrifugal methods of CNFs suspension,combined with ultrasonic dispersion method and orthogonal experiment.The results show that polycarboxylic acid water reducer(PCs)with dispersing time of 30 min,concentration of dispersant of 0.6g/L and dispersing power of 40% is the best combination for effectively dispersing CNFs.Surface carboxylic acidification of CNFs was carried out using FT-IR technique to measure chemical groups.It turns out that after carboxylic acidification,the-OH and-COOH groups turned on the surface of acidified CNFs to enhance the surface activity of CNFs.The effect of different CNFs content on the mechanical properties of cement paste and mortar was studied by strength test.The micro-morphology and pore structure of cement paste and mortar were analyzed by SEM and MIP.The results show that 0.10 wt.% CNFs has the best effect on the mechanical properties of cement paste and 0.15 wt.% CNFs has the best effect on the mechanical properties of cement mortar,and CNFs can play a bridge and network filling role in cement-based materials and can refine the pore size and reduce porosity.The tests of internal corrosion mixed with sodium sulfate and external long-term immersion of sodium sulfate were carried out to study the sulphate-corrosion resistance of CNFs reinforced cement paste.The experimental results show that CNFs can reduce the crack development of the specimen surface and prevent the reduction of strength.Wet-dry cycles in different concentproportionn of sodium sulfate solution and long-term immersion in the same concentproportionn of different salt solution were used to study the effects of different CNFs content on the sulfate resistance of cement-based materials.The experimental results show that CNFs can improve the corrosion resistance of cement-based materials.By testing its compressive and flexural strength,mass loss rate and relative dynamic modulus of elasticity,it can be seen that when the CNFs content is 0.15 wt.%,the corrosion resistance of cement-based materials could be effectively improved.Through surface observation,the surface of the control group samples obviously spalled more,quartz sand aggregate exposed.The strength and mass loss of samples were tested to study the freeze resistance test of CNFs cement mortar.The results show that CNFs can improve the freeze resistance of cement-based materials especially when the content of CNFs is 0.15 wt.%.And deduce that the mechanism of strengthening is that CNFs can reduce the porosity and play a bridge role.