Study On The Action And Mechanism Of Nano-SiO₂ Formation On Cement-based Materials

Improving the performance of concrete is the focus of research on cement-based concrete materials in the 21 st century,and the modification of cement concrete by using ultrafine minerals is one of the main ways of concrete material evolution.The nano-SiO₂ precursor solution is an acidic solution in which nano-SiO₂ particles have not been precipitated.After being added to the cement slurry,SiO₂ in the solution is precipitated as nanoparticles,and can be uniformly dispersed in the cement slurry.This method not only can eliminate the agglomeration problem of the nanometer ore powder,but also has a simple preparation process and low cost.Also it has great significance for using nano materials to improve the performance of the concrete.The p H value of the precursor solution,the concentration of water glass,the type of acidic medium and its concentration on the precursor solution are analyzed by experiments.And studing the preparation method of nano-SiO₂ precursor solution with the most effective precipitation effect.The hydration mechanism of cement-based materials in nano-SiO₂ is analyzed by hydration heat test and SEM energy spectrum analysis.Based on the above research,the influence mechanism of the amount of precursor solution and the p H value of the precursor solution on the rheological properties of cement-based materials in nano-SiO₂ is analyzed.The mechanical properties of cement-based materials generated in nano-SiO₂ show that the precursor solution has better effect on the compressive strength of cement-based materials than nano-mineral powder.When the p H value of the precursor solution is 6,and the amount of acetic acid solution in the precursor solution is 8.9% of the mass of the cement,the compressive strength of the mortar specimen reaches a maximum value and is higher than that of the nano-mineral powder in the same solid content.The micro-test results of cement-based materials in nano-SiO₂ show that when the amount of nano-SiO₂ precursor solution is mixed,it can not only accelerate the dissolution of Ca2+ in cement particles,but also accelerate the formation of a large amount of C-S-H gel.The elongated C-S-H gel starts from the cement attachment and grows inward while growing outward.The in-growth C-S-H gel closely connects the cement particles with the thin hydrated calcium silicate shell,and the outwardly grown C-S-H gel tightly bonds the different cement particles together to form the structure of the C-S-H gel network skeleton.The results of rheological properties of cement-based materials in nano-SiO₂ show that the hydration speed of cement slurry with pre-mixed solution is accelerated,and theflocculation structure formed by hydration greatly increases the force between cement particles.With the increase of the amount of nano-SiO₂ precursor solution and the increase of p H value,the yield stress and plastic viscosity of the cement slurry gradually become larger,the rheological properties of the slurry deteriorate rapidly,and the slurry rapidly condenses.