To date, almost none modern construction site can do without the use of cement. Ease of use and financial accessibility make this material indispensable for most construction works. Therefore, it is very important that the cement stone obtained during construction meets the necessary requirements when erecting construction projects. The theoretical aspect of the issue of dependence of the water-cement ratio on strength is considered in the article. A number of experiments were performed, taking into account the experience of other researchers with the aim of determining the reliability of data, obtained earlier. The results obtained during the experiment confirmed that the increase in water-cement leads to a decrease in the strength of the cement stone.

Keywords: Cement, water, water-cement ratio, active cement, concrete, sand, strength, compression, dispersion, Portland cement

One of the most important systems for ensuring the required air quality in Orthodox churches is the ventilation system. Mechanical ventilation is getting contaminated during operation. The air, passing through the air ducts, contains dust particles, including pathogenic bacteria. To prevent bacteria from multiplying in the ventilation system, bactericidal filters must be used. Halls of Orthodox churches belong to public buildings with a large crowd of people with a long stay. Such premises require a bactericidal efficiency of at least 90%. For the ventilation systems of the church of St. Theophan the Recluse, the authors proposed and implemented a device for bactericidal air treatment using ultraviolet radiation. The bactericidal effectiveness of this device was 92%, which is higher than required. The authors recommend using the proposed device for public buildings.

Keywords: Orthodox church, church buildings, ventilation of religious buildings, bactericidal treatment of air, ultraviolet radiation, air disinfection, bactericidal effectiveness