The results of experimental studies aimed at improving the strength characteristics of cement stone and fine-grained self-compacting concrete through the use of polyfunctional modifying additives based on nano-silicon dioxide (nano-SiO2) and micro-dispersed mineral components are presented. It was established that the introduction of 0.03% nano-SiO2 by weight of cement increases the compressive strength of cement stone by up to 32%, which is associated with the intensification of clinker mineral hydration processes, the formation of an additional amount of low-base calcium hydrosilicates, and an increase in the number of crystallization centers in the early stages of hardening. The effectiveness of the combined use of nano-SiO2 with microsilica and micro-calcite, which are similar in composition to cement but differ in structure and functional activity, has been experimentally confirmed. The use of two-component systems made it possible to increase the flexural strength of cement stone by up to 29% compared to the reference samples. The greatest effect was achieved by adding a polyfunctional three-component additive, including nano-SiO2, microsilica, and micro-calcite, to the composition of fine-grained self-compacting concrete. The use of this system increased the compressive strength of concrete by 44% (to class B60) and the flexural strength by up to 12.5 MPa (an increase of 53.7% relative to the reference composition). It was additionally established that the complex of additives contributes to the acceleration of self-organization processes in the early stages of hardening by increasing the density of crystallization centers and a more uniform distribution of hydration products in the cement matrix volume.

The problem of designing mix compositions for fine-grained self-compacting concrete is addressed. The relevance of the study is associated with the limitations of conventional approaches based on the principle of densely packed aggregate systems. It has been established that existing methods, including those proposed by Okamura, are not sufficiently effective for high-strength multicomponent systems. In this study, a new mathematical model is proposed based on the criterion of excess of the cement-dispersed matrix over the sand volume (Ipcd) and the criterion of excess of the cement-dispersed-sand rheological matrix over the coarse aggregate volume (Ishchcdp). A fine-grained self-compacting concrete mix incorporating stone powder and microsilica has been developed. Experimental results demonstrated intensive strength development kinetics: more than 60% of the compressive strength is achieved within the first 3 days, frost resistance in aggressive environments reaches the F200 level, and a linear increase in transverse deformations is observed up to medium load levels. The research was conducted within the framework of the scientific project IRN AP27511185 «Energy-saving technology for the production of non-prestressed reinforced concrete products using fine-grained self-compacting concrete».

The use of fly ash as a supplementary cementitious material in concrete is increasingly important due to environmental sustainability and enhanced performance requirements. This study examines the effect of fly ash replacement levels of 10%, 20%, and 30% by cement weight on the properties of B20-grade concrete. Fresh concrete showed reduced workability: slump decreased from 200 mm to 190 mm, 158 mm, and 136 mm (by 5%, 21%, and 32%), while air content dropped from 3.1% (control) to 2.8%, 2.9%, and 2.5% respectively. Hydration heat monitoring revealed significant reduction in peak temperature from 26.2°C (plain concrete) to 25.8°C, 25.7°C, and 25.0°C. Compressive strength at 28 days reached 97%, 86%, and 72% of the control mixture. The results confirm that 10–20% fly ash replacement optimally reduces hydration heat in massive structures while maintaining sufficient strength development, offering practical recommendations for sustainable concrete design in construction practice.

This study presents a multiscale investigation of cement-based systems modified with silica fume (SF) and fly ash (FA) for self-compacting concrete (SCC). Cement pastes and mortars with replacement levels of 0%, 5%, 10%, and 15% were evaluated for rheological behavior, hydration kinetics, and microstructural evolution using rotational rheometry, semi-adiabatic calorimetry, scanning electron microscopy, and X-ray diffraction. The results show that SF increases plastic viscosity and promotes structural build-up due to its high specific surface area and pozzolanic reactivity, while its influence on yield stress depends on dispersion conditions and superplasticizer efficiency. In contrast, FA reduces both yield stress and viscosity, improving flowability due to its spherical particle shape. Thermal analysis indicates that SF modifies hydration by reducing and slightly delaying the main exothermic peak at higher dosages, whereas FA mainly lowers the peak temperature with limited effect on its timing. Microstructural analysis reveals that SF contributes to a denser, more homogeneous matrix through pore refinement and increased C–S–H formation, whereas FA systems exhibit a more heterogeneous structure with slower early-age development. The results demonstrate a clear relationship between rheology, hydration, and microstructure. The combined use of SF and FA has been shown to be an effective approach to improving the performance and sustainability of SCC.