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Title: Hardening of Concrete with Hydrothermal Nanosilica

Author(s): VadimV. Potapov, Yuriy V. Efimenko, Alexander A. Karabtsov, and Denis S. Gorev

Publication: Symposium Paper

Volume: 326


Appears on pages(s): 15.1-15.10

Keywords: concrete strength, hydrothermal solution, nanopowder, puzzolanic reaction, silica, sol

DOI: 10.14359/51710985

Date: 8/10/2018


Experiments were carried out to obtain sols and nanopowders of SiO2 on the basis of hydrothermal solutions. Processes of orthosilicic acid polycondensation, ultrafiltration membrane concentration and cryochemical vacuum sublimation were carried out to achieve the result. Physical and chemical properties of sols and nanopowders of SiO2 were determined with the help of the set of methods. Samples of silica sols and powders were characterized by Dynamic Light Scattering, Scanning and Tunneling Electron Microscope, X-Ray Diffraction, BET Surface Area. In particular, it was shown that diameters of SiO2 nanoparticles in sols and nanopowders were in the range of 5-100 nm. The possibility of obtained silica use as a modifying additive for concrete strength increase was substantiated. The test results on concrete compressive strength rise using nanosilica additive extracted from hydrothermal solution are presented. Experiments were made using nano-SiO2 in the coarse-grained concrete of the same mobility mixtures with the same water-cement ratio W/C=0.715 when SiO2 consumption was 2.0 wt. %, and the consumption of superplasticizer polycarboxilate (PCX) was 1.0 wt % with respect to cement consumption. The addition of sol in conjunction with the PCX significantly increases the strength of concrete in all periods and in all modes of hardening. The compressive strength after 28 days was 40% higher compared to reference sample without additives of nano-SiO2, while in the initial stages of hardening (1 day) this indicator reaches 90-128 %. It was obtained by X-Ray diffraction and thermogravimetry that SiO2 can increase the rate of calcium silicates hydrates formation in puzzolanic reaction through its great specific surface area and high density of surface silanolthat leads to increasing strength.