Modification of Cement Composites with Hydrothermal Nano-SiO2: Fid-Bau Portal

Modification of Cement Composites with Hydrothermal Nano-SiO2

Potapov, Vadim / Efimenko, Yuriy / Fediuk, Roman / Gorev, Denis / Kozin, Andrey / Liseitsev, Yury

The modification of cement concretes with various silica-containing additives is an urgent task that can significantly improve their physical and mechanical properties, as well as operational characteristics. In this paper, ${SiO}_{2}$ sols and nanopowders based on a hydrothermal solution were obtained by a technological method using ultrafiltration membrane concentration. The physicochemical characteristics of silica nanoadditives were measured by dynamic light scattering, the BET (Brunauer–Emmett–Teller) method of low-temperature nitrogen adsorption, scanning and tunneling electron microscopy, and small-angle X-ray scattering and thermogravimetry. Sol and nanopowder with particles $6.6 nm$ in diameter, a specific surface area of ${410 m}^{2} / g$ , and a density of reactive silanol groups of Si-OH $4.9 nm$ were used as modifiers of the solutions. The level of increment in compressive strength $R_{com}$ turned out to be lower for all dosages of ${SiO}_{2}$ than after modification with the sol. At low ${SiO}_{2}$ dosages (0.01%–0.25%), the increment in compressive $R_{com}$ , flexural $R_{flex}$ strength, and density $ρ$ rose with an increase in the ${SiO}_{2}$ dosage much more rapidly than at high dosages (0.5%–3.0%). The relations $Δ R_{com} / {[SiO}_{2}]$ , $Δ R_{flex} / {[SiO}_{2}]$ , and $Δ ρ / {[SiO}_{2}]$ can be approximated by the same type of equations like $Δ R / {[SiO}_{2} {] ([SiO}_{2}]) = A / {[SiO}_{2}]^{z}$ , where coefficients $A$ and $z$ depends on the age of the solid samples. The level of ( $R_{com}^{1} / R_{com}^{28}$ ) for the nanopowder was lower than for sol, especially at the lower dosages of ${SiO}_{2}$ 0.01%–0.5% by weight. The ratio $R_{flex}^{28} / R_{com}^{28}$ changed in a relatively small range of values from 0.14 to 0.18 for sol and 0.16–0.23 for nanopowders. A modification with the hydrothermal ${SiO}_{2}$ sol and nanopowder at dosages of 0.25%–0.50% and higher allows one to bring the grade of cement material to a level of low abrasion. The possibility of modifying concrete products with large dimensions by dosing liquid hydrothermal sol ${SiO}_{2}$ and increasing the product’s durability by 3–6 times in a uniform manner is shown.