Research On The Mechanism Of Modifiing Cement-Based Materials By The Use Of Nanopowders

At the present time that cement-based composite materials are researchedin many countries with the help of great investment, The cement-basedcomposite materials are not only the building materials but also new technologymaterials for severed utilitiesafter improving the cement properties, and then thestudy on cement-based materials will become the other direction of studyingmaterials and an important branch of cement-based composite materialdevelopment in future. Improming properties of cement-based materials withhelp of technology nanometer materials technologies are very important and thetechnologies of HPC are promoted further.The progress and problems on cement-base composite material research aredetially summaried in this thesis. The hydration theories of composite cementadded ultra-fine powders were discussed, and the nanopowders inductionhydration theories were proved.Through experiments of cement paste, the influnce of cenment paste wereresearched for diffierent amount of nanopowders added in cement paste. Theresults showed that amount of the water used increased and setting time changesdecreased when adding nano-SiO₂ powders in cement paste, however, amount ofthe water used decreased and setting time decreased when adding nano-ZrO₂powders in cement paste. The soundness of these kinds of composite cementpaste above still was better.Through strength experiments of cement mortar, the compressive strength were remarkably enhanced, when amounts of nanopowders added were little andreduces water agent (UNF-5) existed at the same time, By impermeability test ofcement mortar, the results indicated that the impermeability of cement mortarwas remarkably enhanced, and this principles of changing were consistent withthese strength of changing cement mortar.Through the cement mortar hydration experiments, the rate of hydrationheat released quikly and the max exothermic temperature was obviouslyenhanced after nanopowders of SiO₂.The rate of hydration heat released slightlyat first, after eight hours hydration released quikly and the max exothermictemperature also was slightly enhanced after nanopowders of ZrO₂. Therefornanopowders can promot hydrating process in the cement paste.By modem test methods, such as SEM and XRD, the microstructure ofcement hardened mortar humidity was analyzed. The results showed thatnanopowders of SiO₂ or ZrO₂ cound not only increase the rate of hydration andalso could improve remarkably the microstructure of cement hardened mortarhumidity, such as counld increased density of hydration products and increasedamount, of these in cement mortar, and counld reduced the percentage of poresand the distrabution of pores and so on. The effects above enhanced the strengthof cement mortar.That nano-SiO₂ and nano-ZrO₂ could improve effectively the internalmicrostructure of cement hardened mortar humidity. Nano-SiO₂ powders couldabsorpted Ca(OH)₂ to produce the C-S-H gel and reduced the size of Ca(OH)₂crystals; Moreover, The nanometer induction hydration of nano-ZrO₂ powderspromoted cement mortar hydration deeply, induced hydration could produceswere formed, for example ,C-S-H gel, AFt/AFm ect. Although the two kinds ofnanopowders differently influnced the process of cement mortar hydration, butboth had a function to improve hydration process. The properties of cementmartor, such as the mechanics properties, the physical performance and thedurability were improved.