Research On The Effect Of Nano Materials On Cement Paste System And Its Mechanisms

This research focuses on the role and mechanism of nano SiO₂ and nano CaCO₃ in cement paste.Adding nano materials in cement can significantly improve the performance of the cement paste.But it also brings some adverse effects.The working performance,mechanical properties,mechanical properties and electrical resistivity of the cement paste were studied by means of some experiments combined with electron microscope scanning.In this study,the fluidity of cement paste mixed with different kinds and different doses of nano materials were tested under the same proportion.The test results show that the fluidity of cement paste decreases with the increasing of nano material dosage.This is because adding nano materials in cement paste could increase the amount of water required in the surface of the cement particles.Thereby the amount of water between the cement particles is reduced.The fluidity of cement paste mainly comes from the moisture content between the cement particles,so it can decrease the fluidity of cement paste after adding nano materials.In the mechanical properties test,mixed with a certain amount of nano materials in cement paste can improve the compressive strength and flexural performance of cement paste,but when the nano material content is too high,it will reduce the strength of the specimen.When the content of nano SiO₂ is 1%?relative to the mass fraction of cement?,the compressive strength and flexural strength is the highest;when the content of nano CaCO₃ 1.5%?relative to the mass fraction of cement specimens?,flexural strength and compressive strength is also the highest.This is because the nano material can fill the tiny holes,improve the internal microstructure,and make cement paste more dense,so as to improve the compressive strength and flexural strength.From the experiment of drying shrinkage of cement paste,we can find that the specimen shrinkage with the incorporation of nano materials appears different degrees of growth compared with ordinary specimens.The shrinkage is highest when the incorporation of nano SiO₂ is 1% or the nano is CaCO₃ is 1.5%.With the incorporation of nano materials,the internal humidity of cement paste will be reduced.At the same time,the number of meniscus will increase which makes the specimen shrinkage rate rise.By monitoring in the resistivity of cement paste,we found that the resistivity of cement paste with nano materials inside is higher than that without nano materials inside,and each stage of the hydration appears in advance.This is because the incorporation of nano materials could fill the tiny pores of cement paste,while internal humidity is also decreased,so that the resistivity of cement paste with nano materials increases.In addition,the surface energy of nano materials is very high,and it can accelerate the hydration reaction of cement,so that the various stages of hydration is ahead of time.We analyzed the microstructure of the specimens by using electron microscopy?SEM?and other techniques.Because the size of nano materials is very small,it can be effective to fill some holes and defects inside the specimen.Through the observation of the microstructure,it was found that the density of the specimens was greatly improved compared with the ordinary specimens.