For development of the potential of nanosilica application in Portland cement concrete the effect in compressive strength Rcom increase was studied in the age from 1 to 360 d. Sol of hydrothermal nanosilica (HNS) solution produced by technology developed was used with SiO2 particles Brunauer-Emmett-Teller surface area of 500 m2/g. Concretes compositions were tested with liquid/binder ratio 0.5 and SiO2 doses of cement replacement 0.5, 1, 2, and 3 wt.%. Modification of concrete with HNS sol provided a significant increase in compressive strength Rcom up to 86.4% (14.8%–43.9% at the age of 360 d) and high values of efficiency coefficient kec 19.5–60.9 at the age of 28 d calculated using the relative increase of Rcom. Increase in compressive strength is characterized by an early gain in Rcom at the age of 1–7 d: the ratios R com 1,7 /R com 28 and R com 28 /R com 360 are higher in modified concrete. The obtained results can be used to model the hardening and predict the strength of modified concrete at the age of 2, 4, and 10 y. Results of the thermogravimetry, X-ray diffraction, scanning electron microscopy and water absorption methods provided explanations of pozzolanic reaction effects on compressive strength, water impermeability, abrasion and frost resistance, impact viscosity and durability were discussed. The dependence of kec coefficient on SiO2 dose and concrete’s age was analyzed. Using the coefficient kec for different doses of SiO2 at the age of 28 d, the corresponding clinker’s savings coefficient (23.4%–37.6%) and reduction of CO2 emissions to the atmosphere during the production of Portland cement were calculated. Economic evaluations of the efficiency of using HNS in Portland cement concrete were made in comparison with different materials: commercial nanosilicas and pozzolans such as condensed silica fume, metakaolin, fly ash; metal oxides TiO2, Al2O3, Fe2O3, ZrO2 and multi-walled carbon nanotubes nanopowders.
