Introduction. The article is devoted to the study of the features of the use of combined steel-reinforced concrete floors made on the basis of lightweight steel thin-walled structures in the construction of buildings in seismic areas. These structures are lightweight, have a high load-bearing capacity relative to their own weight and accelerate the construction process. Together, these properties make them a competitive alternative to traditional technologies used in the construction of buildings erected in seismic areas.

The aim of the study is to review, demonstrate the current progress, problems and future directions of research, features of the use of combined steel-reinforced concrete floors of buildings based on lightweight steel thin-walled structures in seismic areas.

Materials and methods. A systematic review and analysis of domestic and international studies on the seismic resistance of composite steel-reinforced concrete floors based on lightweight steel thin-walled structures were conducted. The study used systematization, structural, comparative, and correlational analyses, as well as theoretical generalization of materials obtained from normative and technical documents and research literature regarding the seismic performance of these floors.

Results. The findings of experimental studies on the seismic resistance of composite steel-reinforced concrete floors based on lightweight steel thin-walled structures were reviewed and summarized. Current achievements, pressing challenges, and future research directions were demonstrated. The analysis confirms that these floors offer a competitive and effective solution for construction of buildings being erected in regions prone to seismic activity. The synergy between the steel frame, profiled decking, and concrete layer ensures an optimal balance of stiffness and ductility, which is critical for resisting seismic loads and ensuring structural reliability and mechanical safety. However, the lack of normative documents regulating the design of such floors in seismic regions hinders their broader adoption in construction practices.

Conclusions. The study confirms the necessity for theoretical and experimental research, as well as the development and refinement of normative and technical documents. These efforts will facilitate the wider application of composite steel-reinforced concrete floors based on lightweight steel thin-walled structures, ensuring the reliability and mechanical safety of buildings constructed with their use, particularly in regions prone to seismic activity.

Introduction. Transport tunnels and metro systems are complex engineering structures subjected to significant loads and diverse environmental impacts, necessitating a systematic approach to ensuring their operational reliability. Concrete and reinforced concrete structures, which form the backbone of these facilities, frequently experience damage that compromises their functional characteristics and safety. The need to update and systematize approaches to repairing of such structures has become urgent due to updating of the regulatory framework, increasing demands for infrastructure resilience, and the adoption of advanced technologies.

The aim of developing the draft Code of Practice is to establish the technical foundations for designing, organizing, and conducting of the repair and restoration work on concrete and reinforced concrete structures of transport tunnels and metro systems. This applies to structures under construction, in operation, or temporarily taken out of service, which are subject to constant exposure to water and water vapor, loads, and impacts from surrounding rock masses. The work also considers the possibility of restoration being limited to the internal contour of the lining or the structural elements of subsurface sections.

Materials and methods. As part of the work, an analysis of existing regulatory documents in the field of repair of concrete and reinforced concrete structures was carried out, along with the review of provisions and recommendations of international organizations. Additionally, the results of research and development (R&D) were studied and taken into account.

Results. The result of the work is a Draft Code of Practice that includes key provisions for the design, organization, and implementation of repair works, including methods for restoration, reinforcement, and sealing of the structures. The project incorporates modern repair technologies and takes into account the operational specifics of underground transport facilities. The document has undergone a stage of public discussion, received expert evaluations from professional communities and authorities, and is being prepared for approval and implementation.

Conclusions. The implementation of the Code of Practice will enhance the quality and reliability of repair works, reduce costs, and extend the intervals between repairs, thereby contributing to the sustainable development of transport infrastructure.

Introduction. One of the most important reserves for saving material and energy resources in the construction industry is the re-involvement of recycled (concrete) crushed stone in the production sector, in particular for the production of heavy concrete of classes B7,5–B35 for general construction purposes. Solving this problem will practically ensure the implementation of the most important principle of waste-free technological processes (in the production of precast and monolithic concrete and reinforced concrete structures) and create conditions for fulfilling important social, economic and environmental tasks.

Aim. Conducting experimental studies to determine the standardized durability characteristics of concrete and reinforced concrete based on recycled (concrete) crushed stone and natural sand, as well as comparing them with similar concretes based on natural crushed stone and sand.

Materials and methods. For the research, recycled (concrete) and granite (natural) crushed stone according to State Standard 8267-93 were used as coarse aggregates. Natural sand according to State Standard 8736-2014 was used as a fine aggregate. Portland cement according to State Standard 31108-2020 was used as a binder. Superplasticizer C-3 according to State Standard 24211-2008 was used as an additive. The mixing water was used according to State Standard 23732-2011.

Results. Concretes based on recycled crushed stone and natural sand have slightly lower strength, density and identical indicators of water resistance and frost resistance compared to similar concrete based on natural crushed stone and natural sand.

Conclusions. Based on the results of the work carried out, it was revealed that concrete based on recycled crushed stone and natural sand ensures the initial passive state of steel reinforcement and retains the passive state of steel reinforcement for a long time (more than 100 years) with a protective layer thickness of 10 mm. Concretes based on recycled crushed stone and natural sand can be used as traditional structural concretes for general construction purposes.

Introduction. One of the most important properties of facade plasters is their ability to resist the effects of atmospheric moisture or hydrophobicity. Water penetrates into the facade plaster layer by adsorption. In this case, the passage of moisture through the plaster solution is caused by capillary action (water absorption, moisture permeability).

Hydrophobization is a sharp decrease in the ability of materials to be wetted with water and aqueous mortars while maintaining vapor permeability. In this paper, a comparative study of the moisture-proof properties of lightweight mineral hydrophobic plaster based on foam ceramic granules "SPADAR", plaster mixtures with other similar lightweight fillers, in relation to aerated concrete. The values of capillary water absorption of plaster compositions, as well as water absorption by weight and the depth of water penetration into the body of aerated concrete samples uncoated and coated on all sides with the studied plaster compositions were compared.

Aim. To investigate the moisture-proof properties of a plaster composition with foam ceramic granules "SPADAR" and similar plaster compositions (on foam ceramic granules "KERWOOD" (another manufacturer), granular foam glass and perlite sand) in relation to aerated concrete.

Materials and methods. To conduct the study, previously developed lightweight hydrophobic plaster compositions for facade work with a dry density of no more than 600 kg/m³ and aerated concrete samples with a density of 600 kg/m³ were used. Water absorption by weight values of a control sample of aerated concrete, as well as aerated concrete samples coated on all sides with the studied hydrophobic plaster solutions were compared. The depth of water penetration into the body of these samples was also compared.

Results. Water absorption by weight of control samples of aerated concrete and plastered with lightweight plaster mortars and the depth of water penetration into the aerated concrete layer after 1.5 hours were established. The advantages of the plaster composition using foam ceramic granules "SPADAR" are revealed.

Conclusions. Based on the data obtained, the composition of a light hydrophobic plaster mortar was developed using foam ceramic granules "SPADAR" and further studies of these plaster compositions on vapor permeability and frost resistance are planned.

Introduction. The problem of “monolithicity” of structural concrete under construction has been and remains one of the most controversial in acceptance control in construction practice. The lack of clear criteria for assessing of cold joints presence arising during forced breaks in concreting, as well as differences in concreting conditions and properties of concrete mixtures, are among the main factors causing uncertainty in making a decision to reject the erected structure, or making a decision on the need for repair measures, or recognizing the erected structure complies with the project and does not requiring additional costs to ensure the design operational reliability. Lack of homogeneity of physical and mechanical properties of concrete separate parts of the monolithic structure creates stress-strain states of the power frame of the building that are not foreseen by the project and can provoke a threat to the safety of the structure, and lead to a reduction in the inter-repair service life of load-bearing structural elements.

Aim. The aim of the work is to clarify the conditions of cold joints occurrence when concreting depending on the technological properties of concrete mixtures and laying technology, to develop methods of their diagnosis, as well as the subsequent specification to define of the term “cold joint”, its characterization and formulation of proposals in order to make appropriate changes in regulatory documents.

Results. The results of the performed experiment do not support the requirement of the regulations to consider the boundary of the onset of setting as significant in terms of damage to the structure of concrete and the ability to have a noticeable effect on the drop in average strength due to the “loosening” of the “coarse aggregate – mortar” system. Despite the fact that in the series of such experiments it is required to consider more extended statistics, the obtained trends reduce the probability of identifying the beginning of setting as an indicative boundary of the rheological state, when the influence of vibration on reducing of concrete strength after its subsequent curing under favorable conditions becomes determinant.

Conclusions. The formulated and duplicating each other requirements of normative documents on the boundary condition of loss of conditional “continuity” of concrete properties in the body of the structure at simultaneous placement require revision and clarification based on the analysis of the previously performed and additionally conducted experimental studies.