The thesis paper for the degree of Doctor of philosophy in specialty 192 "Construction and civil engineering". – Kyiv National University of Construction and Architecture, Ministry of Education and Science of Ukraine. Kyiv, 2023.
The thesis paper is devoted to solving the problem of restoring the protective layer of reinforced concrete structures. In the analyzed scientific works, methods of repairing the protective layers of reinforced concrete structures of horizontal (floor) and vertical (side) surfaces are mainly considered. At the same time, it is proposed to restore the lower surfaces of span structures by shotcrete, manual application of repair mixtures, or embedding the mixture in the formwork. In turn, research aimed at restoring protective layers by forming a mixture into the formwork is virtually nonexistent, and the experience of using this technology specifically for restoring the lower surfaces of span structures is a rare example. This means that this work is aimed at solving an urgent scientific problem, the results of which will make it possible to form a scientifically based technology for restoring the protective layer of reinforced concrete structures.
In the introduction the relevance of the direction of scientific research is substantiated, the purpose and main objectives of the research are formulated, the object and subject of research are determined, the scientific novelty and practical value of the results obtained are revealed.
In the first section the prerequisites for the relevance of studying the technology of restoring the protective layer by forming a repair solution into a formwork are considered. In the direction of scientific work, well-known technologies for repairing reinforced concrete structures were analyzed and their advantages and disadvantages were determined. The main factors that worsen the condition of reinforced concrete structures are also identified and classified. Technological factors that can affect the design parameters of restored reinforced concrete structures and shape the technology of work are identified.
In the second section an analytical study aimed at determining the importance of technological factors that have the greatest impact on the design parameters of restored parts of reinforced concrete structures was carried out. A general research methodology which is based on theoretical studies aimed at identifying technological factors that arise in the process of repair and restoration works and experimental studies aimed at identifying dependencies of the influence of such factors on the design parameters of the restored structure.
In the third section the methodology of experimental research is presented, according to which research work was carried out in stages to identify the influence of technological factors on the design parameters of the restored structure.
On the first stage experimental studies have determined how the mobility of the repair mixture affects the quality of filling the formwork structure during restoration and the strength of adhesion of the repair layer to the base.
Also, the first stage of experimental studies provided for determining the influence of the method of preparing the concrete surface and the spatial position of the repair site relative to the horizon line on the adhesion strength of the repair solution to the restored concrete.
On the second stage the influence of the state of preparation of concrete samples' surfaces and the spatial position of the repair surface on the strength of the joint layers was determined.
At the third stage of experimental tests studies have established the influence of the humidity of the restored surface and the duration of vibration of the formwork during the restoration of samples on three surfaces (top, side and bottom) on the design parameters of the restored structure.
On the fourth stage experimental studies have determined the dependence of the adhesion strength of the repair layer to the base on its thickness. At the same time, studies were conducted aimed at determining the effect of ambient temperature on the adhesion strength of structural layers.
At the final stage, a study of the technical and economic indicators of the improved restoration technology and alternative technologies for repairing the protective layer of lower span reinforced concrete structures was carried out.
In the fourth chapter the main provisions of the technology for restoring the protective layer of reinforced concrete structures by embedding the repair mixture in the formwork are developed and described. The proposed technology was tested in semi-natural and full-scale conditions.
Keywords: reinforced concrete, protective layer, restoration, repair mortar, formwork, technological factors, adhesion strength.
