Research On The Influence Of Nanocellulose On The Performance Of Cement Concret

The rapid development of the construction industry has caused serious damage to the environment,and the consumption of building materials such as cement accounts for a large part of this,so the search for a new green and environmentally friendly material is an urgent problem.Nanocellulose is mainly extracted from plants and is a major component of plant cell walls.Given its low density,low toxicity,low cost,high aspect ratio,high specific surface area and excellent mechanical properties,nanocellulose has become a promising nanofibre material for improving the properties of cement paste.In this thesis,we will investigate the effects of different CNFs admixtures on the properties of concrete and cementitious materials through pretreatment of CNFs,testing of mechanical properties of concrete,testing of chloride ion diffusion resistance and frost resistance,and experiments on hydration,microstructure and rheological properties of cementitious materials.The main studies are as follows:(1)To study the effect law of dispersion of CNFs on the mechanical properties of concrete,and to test the mechanical properties of CNFs modified cement concrete with different predispersion treatments,it was found that CNFs could effectively improve the mechanical properties of concrete after dispersion,and different pre-dispersion methods would affect the modification effect of CNFs,and the pre-dispersion DP5L2 type CNFs The pre-dispersed DP5L2 CNFs had the most significant effect on the improvement of the mechanical properties of concrete.(2)Different amounts of CNFs were added to the concrete to investigate the effect of CNFs on the mechanical properties of concrete.The compressive and flexural strengths of concrete were tested using a SANS universal testing machine.The results of the study showed that the mechanical properties of concrete showed a trend of first increasing and then decreasing with the increase of CNFs admixture.When the CNFs admixture was 0.15%,the CNFs modified the concrete with the best effect,the compressive strength increased by 33.60% and flexural strength increased by 24.80% compared with the blank group;however,when the CNFs admixture was0.2%,the CNFs admixture was too high and agglomeration occurred,which led to the reduction of the CNFs modification effect.(3)In order to investigate the effect of CNFs on the diffusion resistance of chloride ions and the frost resistance of concrete,different CNFs were added to the concrete and the frost resistance of concrete was tested by the RCM method and the fast freezing method.It was found that the addition of CNFs could effectively prevent the diffusion of chloride ions in the concrete matrix and improve the frost resistance of the concrete.When the CNFs was 0.15%,the depth of chloride ion diffusion in the concrete matrix was reduced by 36.64% compared with the blank group,and the non-stationary chloride ion migration coefficient was reduced by 41.62%;the relative dynamic modulus of elasticity of concrete was increased by 27.11% compared with the blank group,and the mass loss rate was reduced by 2.13 times.(4)Concrete specimens were cut and gold sprayed,and SEM scanning electron microscopy was used to analyze the effect of CNFs on the microstructure of concrete from a microscopic perspective.The test results show that the addition of CNFs can improve the compactness of the matrix,reduce the pores and cracks in the concrete matrix,and effectively improve the structure of hydration products in the matrix.(5)To investigate the effects of CNFs on the hydration and rheological properties of cementitious materials,isothermal calorimetry,truncated cone circular mode method and rotational rheometer were used to test the exothermic pattern of hydration and rheological properties of cementitious materials with different CNFs admixtures.The results showed that the addition of CNFs could delay the early hydration and promote the later hydration of cement,and the slurry of CNFs-modified cementitious materials showed shear thinning,with the increase of CNFs dosing,the flow degree of cementitious materials decreased,and the yield stress and plastic viscosity increased gradually,which was in accordance with the modified Bingham model.When the CNFs dosing was 0.20%,the maximum exothermic rate of hydration of the cementitious material appeared about 7 h later than that of the blank group,but the cumulative exothermic rate was significantly higher at the later stage,indicating that the later stage could promote the hydration of the cement.The flow distance of the cementitious material was reduced by 22.26% compared with the blank group,and the yield stress and plastic viscosity were increased by 1.85 and 2.55 times,respectively,compared with the blank group.