Study And Simulation Of Rheological Properties Of Nano-SiO₂ Modified Cement Based Materials

The introduction of nano-SiO₂ into the cement-based material can modify the material from the microscopic level,effectively improve the mechanical property and durability of the mixture after hardening,but it has a negative impact on the flowability,besides the explanation of influence mechanism on flowability is not mature.With the knowledge of rheology,accurate quantification of the flowability of the mixture can be achieved and linked to various microscopic analyses in order to explain the influence mechanism of nano-SiO₂ in the cement paste.In addition,the flow simulation of nano modified self-compacting concrete is carried out,and the concrete composition suitable for the specific working conditions is determined,based the comprehensive analysis of casting condition and mechanical property.The main research content is divided into the following four points:（1）The initial and time-dependent rheological properties of nano-SiO₂ modified paste with different particle sizes were analyzed,and microscopic interpretation was carried out by free water content,hydration heat analysis,thermogravimetric analysis and Raman spectroscopy.The above research shows that effects of nano-SiO₂ on rheological property can be divided into physical and chemical effects which dominates in turn.The free water content declines caused by nano-SiO₂ adsorbing water on its surface and flocculation structure is the main cause of the decline of flowability in the early stage,and this phenomenon becomes more obvious with the decease of particle size.The difference in the flowability loss over time is due to the various degrees of secondary hydration caused by nano-SiO₂,and the smaller the particle size,the more obvious promotion.（2）The rheological behavior of nano-SiO₂ modified cement paste under different temperature and hydration time were studied,and the above analysis methods were also employed for explanation of rheological changes.The above research shows that the increase of temperature leads to the enhancement of Brownian motion of nano-SiO₂ and thus the adsorption of more water,which brings about the decrease of initial rheological properties.With the extension of hydration time,the differences between growth rate of rheological parameters are more obvious,the reason of this phenomenon is that the hydration activity of nano-SiO₂ increases with temperature,the degree of hydration of cement increases,and the ratio of solid to liquid decreases.（3）Nano-SiO₂ is used in combination with mineral admixture,and the optimal mixture ratio is analyzed by combining the rheological and mechanical properties.The research shows that when the water-binder ratio is low and superplasticizer is used,the paste tends to show a shear thickening phenomenon.By comparing the rheological parameters under different mix proportion,and the compressive strength of the corresponding specimen,it can obtain the best mineral ratios for the experiments are SF3 and GBFS30SF3 based on this experiment with 1.0% nano-SiO₂ content..（4）Based on the measured rheological data of nano modified self-compacting concrete,Flow 3D was used to simulate the concrete flow.Firstly,the model is verified by the regular fluidity tests,and then the typical complex component is selected for the casting simulation.Finally,the most optimal concrete mix proportions which are suitable for the specific structure are chosen with the comprehensive analysis of casting state and compressive strength.This study provides a new idea for selecting the best concrete mix proportion for a component.