Study of Concrete under Combined Action of Aggressive Environment and Long-Term Loading

A significant part of reinforced concrete structures is subjected to intensive environmental impact during operation. This can cause local destruction and failure of buildings if obligatory measures are not taken to protect them from corrosion. This is especially true for industrial buildings, where the environment could be contaminated with aggressive products or waste. An important issue is the development of methods for calculating the load-bearing capacity and serviceability of reinforced concrete structures with corrosion damage. The main reason for this is the necessity to determine the durability and reliability of buildings and structures and the estimation of their safe operation time. As corrosion damages of concrete are a critical issue, more detailed experimental studies are needed. This paper presents experimental studies of concrete prisms under the simultaneous action of an aggressive environment and a constant level of compressive force. In total, 32 prisms under different loading conditions and in different aggressive medium were tested. Samples were divided in series, for which different load levels were chosen (0.25fck, 0.35fck, 0.45fck). Additionally, control samples in the air and immersed in water were tested. During the experiment, different parameters were monitored and recorded: decrease of cross-sectional size, the temperature and environmental humidity. Results of the study showed that destruction occurred due to the presence of corrosion damages of concrete and a reduction of the cross-sectional area. The stresses in the concrete at the destruction stage were less than the value of the prism strength by 10–12%. It was established that along the contour of the section, there is a partially degraded layer of concrete of 1.5–3.7 mm thickness, with corrosion microcracks and corrosion products. Additionally, experimental and theoretical diagrams of concrete with corrosion damages were obtained and compared. The ultimate deformations of concrete with corrosion damage, which correspond to the prismatic strength of concrete, in comparison with undamaged concrete were lower by 11–18%. Therefore, the concrete strength is decreased during exploitation under loading in an aggressive environment, which needs to be taken into account during calculations.

Structural Behaviour of Reinforced Concrete Corroded Column

Worldwide in the construction industry uses reinforced cement concrete. The different types of structures which were built using reinforced cement concrete served for long period. But due to faulty design, improper quality control and corrosion of reinforcement there are notable premature failure and subsequently sudden collapse of the structure occurs. The presence of aggressive medium such as moisture and chloride ions are the main factors which are induces the steel corrosion. The cost involves for repairing the corroded structure escalate very rapidly which leads property loss to the people, if the problem is not corrected. Columns are the main structural members of R.C bridges when exposed to de-icing salt they are more vulnerable to steel reinforcement corrosion. The thorough knowledge about the corrosion can get only by proper investigation. This experimental work mainly focuses on structural behaviour R.C columns subjected to steel corrosion. Columns with two different size were cast and accelerated corrosion was induced. Structural behaviour of the columns were studied with axial load test and compared with conventional specimen. The ultimate load carrying capacity, axial strain, energy absorption capacity were reduced in all the corroded columns

ELECTROCHEMISTRY OF FUNCTIONAL MATERIALS AND SYSTEMS (EFMS)

The work is presented by the V. I. Vernad­skii Institute of General and Inorganic Chemi­stry of the National Academy of Sciences of Ukraine for the State Prize of Ukraine in the field of science and technology. A new paradigm of the processes of electrochemical synthesis of functional materials has been created on the basis of the proposed theory of discharge-ionization of electrochemically active complexes and the laws of correlation between the functional properties of coatings and the fundamental characteristics and parameters of electrochemical kinetics. New approaches of surface engineering to the electrochemical synthesis and processing of materials that are capable of operating under extreme thermomechanical conditions under the simultaneous action of an aggressive medium have been developed. Innovatively promising technologies have been proposed for the formation of nanomaterials of new generation based on superalloys, metal oxide composites, photosensitive hetero- and nanostructures, electrically conductive polymers and their composites, etc. The main research directions in this work concern electrochemistry, both directly the me­thod for the synthesis of new materials and the study and design of the electrochemical pro­perties of materials / coatings / nanoparticles that cannot be obtained by other methods. The aim of the work was to develop the theoretical foundations of directed synthesis and to create a wide range of new competitive materials and systems on the basis of establishing the structural and functional patterns of their electrochemi­cal formation. А number of novel compe­titive electrochemical materials (electrode and electrolyte materials for electrochemical po­wer sources and supercapacitors, electro- and photocatalysts, sorption and optical materials, functional coatings, etc.) have been created as a result of the performed research. These materials are used in various fields of science and technology, namely, for alternative po­wer ge­neration, electrochemical power sources, nano- and microelectronics, electrochromic systems, electrocatalysis, ecosensorics, electro­chemical synthesis of commercial products, photoelectrochemical systems, corrosion protection. The number of publications: 700, including 30 monographs (7 of them published abroad) and 39 chapters in collective monographs (30 of them published abroad), 36 textbooks (manuals), and 500 articles (350 of them published in foreign periodicals). The total number of refe­rences to the publications of the authors/h-index/i10-index (regarding the whole work) according to the databases is, respectively: Web of Science, 1856/21/52; Scopus, 2185/22/71; Google Scholar, 4903/33/148. The novelty and competitiveness of the technical solutions are protected by 33 valid patents (7 patents of Kazakhstan, China, USA). Eight doctoral dissertations (DSc) and 47 candidate's dissertations (PhD theses) on this subject matter have been defended.

Research of Mechanochemical Corrosion of Steels С1020 and А516-55

During operation many metal structures are under conditions of combined impact of aggressive media (natural and/or technological) and mechanical loads. At the same time, the damage caused by the combined effect of corrosion and stress is often more significant than with simple "superimposing" of damage caused by mechanical load and influence of aggressive medium acting separately. When carrying out destructive tensile tests of equipment materials, there is a possibility of inaccuracy of results for determination of mechanical characteristics of this material due to actual operation of the material under conditions of aggressive environment. This, in turn, can lead to an erroneous calculation of the strength and life of the equipment. In this regard, it is particularly relevant to study the behavior of materials under the influence of various mechanical loads in aggressive media, as well as to determine the limit state of the metal based on the results of measurement of its electrode potential.

Corrosion of pipe steels 20 and 17G1S-U in ground electrolytes with a hydrogen indicator close to neutral

Purpose: of this paper is to analyse the mechanism of near-neutral pH corrosion of main gas pipelines. The stages of main gas pipelines in model environments that meet the soil conditions of Ukraine have been studied. Design/methodology/approach: The corrosion rate of steel specimens from steels 17G1S-U and 20 and the influence of borate buffers on their protective properties were evaluated. The influence of corrosion time on changes in pH of model media is shown. Morphological features of surface damages of pipe steels are established. The defect analysis of specimens from steels 17G1S-U and 20 by electron scanning microscopy is carried out. Findings: The effect of borate buffers on the protective properties of the steel grades studied was revealed, and changes in the pH of the model media during corrosion processes were described. The main regularities in corrosion, as well as the surface morphology of damaged specimens, were studied by scanning electron microscopy. Research limitations/implications: Detailed investigation of localised corrosion phenomena induced by inclusions that are present in steels 17G1S-U and 20 is extremely critical. In particular, there is still ambiguity as to whether the localised corrosion initiation induced by non-metallic inclusions is an electrochemical process or a chemical process. Practical implications: The research findings will be used when testing specimens from pipe steels under cyclic loading in the model media studied, as well as for predicting the residual life of gas pipelines with corrosion defects. Their generalization will make it possible to develop the effective methods of ground diagnostics and prediction of SCC of main pipelines. Originality/value: It was found that the corrosion rate is determined by internal (nature and properties of the metal) and external (properties of the aggressive medium and the corrosion process conditions) factors. The protective effect for steel 17G1S in medium NS4 + borate buffer (1: 1) was 61.5%. Steel 20 had the greatest protective effect in medium NS4 + borate buffer (1: 3), which was 87.05%.

Electrochemical Corrosion of Galvanized Steel in Binary Sustainable Concrete Made with Sugar Cane Bagasse Ash (SCBA) and Silica Fume (SF) Exposed to Sulfates

This research evaluates the behavior corrosion of galvanized steel (GS) and AISI 1018 carbon steel (CS) embedded in conventional concrete (CC) made with 100% CPC 30R and two binary sustainable concretes (BSC1 and BSC2) made with sugar cane bagasse ash (SCBA) and silica fume (SF), respectively, after 300 days of exposure to 3.5 wt.% MgSO4 solution as aggressive medium. Electrochemical techniques were applied to monitor corrosion potential (Ecorr) according to ASTM C-876-15 and linear polarization resistance (LPR) according to ASTM G59 for determining corrosion current density (icorr). Ecorr and icorr results indicate after more than 300 days of exposure to the sulfate environment (3.5 wt.% MgSO4 solution), that the CS specimens embedded in BSC1 and BSC2 presented greater protection against corrosion in 3.5 wt.% MgSO4 than the specimens embedded in CC. It was also shown that this protection against sulfates is significantly increased when using GS reinforcements. The results indicate a higher resistance to corrosion by exposure to 3.5 wt.% magnesium sulfate two times greater for BSC1 and BSC2 specimens reinforced with GS than the specimens embedding CS. In summary, the combination of binary sustainable concrete with galvanized steel improves durability and lifetime in service, in addition to reducing the environmental impact of the civil engineering structures.

Investigation of a Steel Local Corrosion in Chloride-Containing Media

Aspects of the development of local corrosion on the metal surface under the influence of aggressive media containing chloride ions are presented. The main mechanisms leading to the formation and development of local damage of the surface of metals are described. The process of electrochemical corrosion of steel under the influence of chloride-containing medium is experimentally investigated. By constructing corrosion diagrams, the main indicators of steel corrosion in a 10% sodium chloride solution were determined, which allows one to judge the rate of development of corrosion processes with local damage to the protective coating and the degree of steel resistance depending on the aggressiveness of the medium. It is shown that protective coatings, such as modified phosphate and oxide-phosphate films, prevent the penetration of an aggressive medium to the surface of the protected metal and, accordingly, the anodic dissolution of the metal.

The changes of LD-PE films after exposure in different media

This work deals with the study of polymers, and, in particular, polyethylene; its production, types, properties, and usage. The experimental part evaluates the changes of properties of the polyethylene film to be reused under various exposure conditions and selection of the most suitable medium for its application. The film made of low-density polyethylene (LD-PE) was influenced by aggressive media with different pH, specifically Savo for the disinfection, Savo as a Saponate for dish washing and Coca-Cola. On LD-PE films the water absorption and melting temperature evaluation tests were performed. Carried out tests show that the most aggressive medium for LD-PE film from used media is Coca-Cola. The most effective application of LD-PE film like wrapping on container transported is the Savo used as a Saponate for dish washing.