Studying the Structure of a Cement Composite Modified by Hydrothermal SiO2 Nanoparticles and MCNTs by the IR-Spectroscopy Method.

The influence of hydrothermal small doses of SiO₂ nanoparticles (NPs) and multiwalled carbon nanotubes (MCNTs) separately and combined with adding a polycarboxylate superplasticizer (SP) at the water–cement ratio W/C = 0.21 has been studied by the IR-spectroscopy method. From the shift of the frequency of absorption of silicon–oxygen tetrahedrons SiO₄ to the region of reciprocal electromagnetic-radiation (EMR) wavelengths 900–1100 cm^–1, it has been established that the nanoparticles added increase their kinetics and the degree of their polycondensation. The influence on the degree of polycondensation of silicon–oxygen tetrahedrons was more significant than on the rate of hydration of clinker minerals and the gross amounts of hydration products of cement. The effect of influence on the kinetics and the degree of polycondensation of silicon–oxygen tetrahedrons depended on the chemical composition of the added nanoparticles (SiO₂, MCNTs, and SiO + MCNTs) and on the age of hardening of the cement composite: it was more pronounced at the age of 28 days than at the age of 1 day for the combination of nanoparticles (SiO₂ + MCNTs) and was absent at the age of 4 h. Increase in the dehree of polycondensation of silicon–oxygen tetrahedrons corresponds to the rise in the crystallinity of a CSH gel and to the increase in the volume density of packing of nanogranules of the gel, and also determines the increment in the mechanical characteristics of the cement composite. [ABSTRACT FROM AUTHOR]