One of the most important elements of the primary protection of concrete structures against chemical aggression is the correct choice of the type of cement. Specialists have done a lot of work to clarify the comparative stability of various types of cement systems in aggressive media containing various aggressive components [1-3]. Resistant cements for certain types of corrosion are known, but there is no complete concept of their choice. This causes difficulties in choosing the type of cement for specific types of corrosion in organic media, for complex types of corrosion, when the application of empirical approaches is unsuitable. This work is devoted to this issue.

It is proposed to distinguish the false setting from the abnormal one, considering the false as a variety of the latter. With false setting, the start of setting occurs in a short time, but then it spontaneously disappears, reappearing after a while. Such cements, in which the beginning of setting occurs faster than 50 minutes, and the end – after 5-12 hours, are proposed to be called abnormal cements. It is shown that when the start time of setting is more than 50 ∼ 60 minutes, the probability of abnormal setting decreases sharply. The kinetics of structure formation of cements with different setting patterns is considered. Methods for the identification of abnormal setting by the setting interval (τfinal – τstart)/τstart > 3, the kinetics of structure formation, heat release, and changes in the activity of calcium ions in the liquid phase of cement paste of normal density are proposed. It is shown that the measurement of the kinetics of heat release and the activity of Ca 2+ ions in the liquid phase of cement paste is of great interest for the development of automated and rapid control of the presence of anomalies during setting. It is established that the mixture of the inhibitor and the booster of the setting acts according to the rule of additivity, the use of mineral additives of acidic composition weakens the abnormal properties of cement systems. To combat the belated anomaly, it is necessary to monitor the properties of the cement 1-2 days before its application.

The paper studies the influence of aggregates and fillers with negative and positive electrical surface properties on the corrosion resistance of concrete. The advantage of resistance of fine-grained concrete on marble sand in comparison with concrete on quartz sand, regardless of the type of aggressive environment, is established. At the same time, the stability of samples of powdered concrete with 10 and 30% of fine-grained filler changed little when replacing the quartz powder with marble one. It is shown that the resistance coefficients of powdered concrete samples with quartz filler (10%) do not differ from the resistance coefficients of samples of a similar composition with crushed marble filler, and with an increase in the dosage of the filler (30 %) slightly exceed. It was found that in powder concretes without aggregates, the contact layer between the cement matrix and the aggregate is absent, so the composition of the mineral powder plays a much smaller role in the corrosion processes of cement stone. The obtained results allowed establishing that electrokinetic phenomena play a secondary role, and the main influence on the stability of fine-grained concrete is the processes of pore colmation by chemical reactions, as well as the interaction of the surface layers of the aggregate with the cement matrix.

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Introduction. One of the problems of developing new generation concrete is to ensure the rational granulometric composition of a mixture of cement and fine additives to ensure the densest packing of all particles of the cement system. In this regard, the paper considers the optimization of the dispersed structure of quartz filler, taking into account its specific surface area, concentration in the composition of the binder and water-solid ratio.Materials and methods. In the studies, Portland cement TSEM I 42.5 N (GOST 31108-2020) of ZAO Belgorod Cement and fine quartz were used. The compressive strength samples were tested on a PGM-100 MG4 laboratory press. The granulometric composition of the fillers was determined using Analysette 22 NanoTec plus laser diffraction particle size analyzer.Results. The conducted studies have allowed to determine that the optimal dosages of microdispersion filler are closely related to the specific surface area and the V/T of the mixture. It is shown that with an increase in the dispersion of quartz filler, a decrease in the range of optimal dosages is observed, which narrows with an increase in the water-solid ratio. The mechanisms of structure formation affecting the properties of dispersed-optimized cement systems are described. With the growth of the specific surface of the filler, the specific activity of the unit of the surface of the filled binder decreases, which is accompanied by a decrease in the number of crystallizationcoagulation bonds between the hydrate phases of cement.Conclusion. The experimental data obtained confirm that for a cement stone made of a mixed binder, the watersolid ratio is no less significant than the concentration of a mineral additive, therefore, a decrease in the V/T of mixed cements is a necessary condition for achieving a given strength.