The article is a continuation of the research on increasing the durability of heavy concrete and extending the life cycle of structures. The objective of the study is to determine the effect of the action of microsilicon and trepel additives introduced into the concrete mixture on increasing the strength characteristics of concrete. A control composition of a given concrete class in terms of strength B60, class F400 frost resistance and W20 water resistance, with the addition of superplasticizer ST 5.0, was selected. A comparative analysis of various concrete compositions was carried out in order to increase their strength characteristics and density. As a result of experiments, it was found that the introduction of 5% silica or trepel, as well as their combinations, helps to achieve a given strength class of B60 and increase the density of concrete. The use of superplasticizer ST 5.0 ensures the necessary mobility of the mixture without increasing the water-cement ratio, which improves the durability and performance of the materials. The results obtained allow us to recommend additives for the production of high-strength concrete with improved technical performance.

Keywords: silica, concrete strength, trepel, concrete mix, superplasticizer, water-cement ratio, heavy concrete, active mineral additives, concrete, MCU-85

The article discusses the use of recycled materials obtained during the dismantling of facilities during renovation in St. Petersburg. The districts of St. Petersburg with "problematic" houses, such as panel "Khrushchev" and "ships" of the first type, are highlighted. Data on the types of waste, volumes of concrete scrap, features and applications of secondary rubble are presented. Examples of organizations in St. Petersburg dealing with waste recycling are given. The purpose of the work is to study the possibilities of recycling construction waste for reuse in construction and landscaping of the region.

Keywords: secondary materials, dismantling, renovation, concrete scrap, construction waste, recycling, crushed stone, sustainable development, St. Petersburg, ecology

The article is devoted to the problems of the use of building waste in the demolition of houses, as well as substandard products at housing enterprises. The issues of concrete scrap processing, methods of its crushing to obtain materials that can be reused to create reinforced concrete products and structures are considered. Concrete scrap has been investigated for compliance with requirements for large aggregate for construction works. Compositions based on conventional coarse aggregate, concrete scrap and conventional fine aggregate have been developed. For the compositions, the technological characteristics of the concrete mixture are determined, as well as the physical and mechanical characteristics of the concrete at 28 days of age. The use of such compositions for the production of reinforced concrete structures is justified.

Keywords: concrete scrap, secondary crushed stone, concrete, characteristics of concrete scrap, recycling, construction waste, large aggregate from concrete scrap, application of concrete scrap