El'Shad Faih Ohly Najafov

This study investigates the finite-element and physical models of railroad sleepers made of concrete with steel and composite prestressed reinforcement. Reinforced concrete sleepers withstand mechanical loads well but have low electrical resistance, which contributes to traction current losses, leakage currents and electrocorrosion of linear structures on electrified railroads, as well as disruption of auto-lock. Since low electrical resistance is due to the electrical conductivity of steel reinforcement, its replacement with composite makes it possible to solve a number of problems in railroad operation. However, its use for sleepers is complicated by the difference from steel reinforcement in elasticity and remains insufficiently studied. Sleeper models and a scheme for their testing have been devised, which corresponds to the standard sleeper test. Calculation and full-scale experiments with loading the models have been performed. It has been established that as the models are loaded and the deformation moment increases, it evolves in three stages: crack formation; their development to the formation of a plastic hinge; failure with reinforcement slipping. In the model with composite reinforcement, compared to steel reinforcement, the moments corresponding to these stages are smaller by values that correlate with lower tension forces and the modulus of elasticity of the reinforcement. The type of reinforcement affects all moments characterizing the strength and crack resistance of the models less than the pre-tensioning forces. The results from the calculated and full-scale experiments have been compared. Correction factors were proposed for calculating the moments of crack formation in sleepers. The results make it possible to design sleepers with composite reinforcement of the required crack resistance. Such sleepers could be implemented provided that a positive result is obtained from their experimental operation on an electrified section of the railroad

Purpose. During operation on electrified direct current railways, reinforced concrete contact network pole of railways are damaged by electrical corrosion. Therefore, the development of alternative support structures, in particular, concrete with composite reinforcement, and the assessment of their bearing capacity is an urgent task. The purpose of the study is to compare the bearing capacity of conical centrifuged poles of the contact network of railways made of concrete reinforced with steel and composite reinforcement. Methodology. The comparison of the load-bearing capacity of the pole of the contact network of railways made of concrete reinforced with composite and steel reinforcement was carried out by means of a calculation experiment with the analysis of the stress-strain state of the risers using the finite element method and the LIRA-SAPR software complex. Findings. A finite-element model of poles with steel and composite reinforcement with the same cross-section and prestress was constructed. Their load during the calculation experiment was carried out until destruction, the calculation was performed in a non-linear setting. As a result of the calculated experiment, the isofield of deformations, stresses in concrete, forces in longitudinal and transverse reinforcement was obtained. It has been established that poles with both steel and composite reinforcement are destroyed due to the development of the working reinforcement. In the stretched zone of the pole with steel reinforcement, cracks do not form before failure, the pole with composite reinforcement works with cracks in the stretched zone. In a pole with steel reinforcement, the distribution of stretched and compressed zones along the cross section is uniform, in a pole with composite reinforcement, a wide stretched zone is observed, precisely in which cracks form, and a minimal compressed zone. The design of the reinforced concrete pole provides the necessary load-bearing capacity of the pole - normative bending moment, the pole with composite reinforcement - does not provide it by 21% due to the 5.4 times smaller modulus of elasticity of the composite reinforcement compared to steel. The deformation of the pole with composite reinforcement exceeds the deformation of the pole with steel reinforcement by 64%. Ensuring the required load-bearing capacity is possible by increasing the cross-section of the reinforcement and the tension of its package. Originality. For the first time, a finite-element model of a conical ring cross-section of a structure made of concrete reinforced with pre-stressed composite reinforcement and the regularity of the distribution of deformations and stresses during bending was obtained. Practical value lies in the creation of an opportunity to design poles of the contact network of railways that are resistant to electrocorrosive influences.

A comprehensive study of the technical condition, corrosion processes, damage and load-bearing capacity of the reinforced concrete chimney pipe, which removes the gas-smoke mixture formed in the technological processes of coke-chemical production and is an aggressive environment, was performed. A methodology for predicting the remaining resource of the pipe structure has been developed. It was established that the damage that determines the ultimate resource is the collapse of the lining, after which active corrosion damage of the reinforced concrete structure occurs. An analysis of the composition and temperature-moisture regime of the aggressive medium was performed. It was established that it is gaseous, the most aggressive components of which are acid gases, the degree of aggressive action is moderately aggressive, possibly strongly aggressive. Corrosion of concrete progresses in a concentric front from the inner surface of the chimney to the outer surface at a rate of 1.2 to 4.8 mm/year. The corroded layer of concrete loses its strength and protective properties to the reinforcement. An analysis of the stress-strain state of the pipe taking into account corrosion damage was performed, the most heavily loaded dangerous zone and its structure were determined, and the limit values of the wall thickness and the depth of corrosion damage in this zone were determined, which ensure the fulfillment of the conditions for bearing capacity. Based on the values of the corrosion rate, the time to reach the limit state is determined. It is shown that without repair and protection measures, the remaining service life of the pipe does not exceed 11 years. It is recommended to carry out a major repair of the pipe as soon as possible with the elimination of damage and restoration of the lining, or no later than after 10 years to carry out the liquidation of the structure with the construction of a new one.

The theoretical substantiation of the production of especially fine-grained concrete (EFC) from the waste of the Poltava Mining Concentration Plant as a fine-grained aggregate has been performed. Its structure is substantiated taking into account the contacts between the angular aggregate grains, the possibility of increasing strength by introducing mineral fillers and microfillers with particles 5 times smaller than the aggregate grains and cement particles, respectively, is proved. The determination of the composition of EFC from the waste of the Poltava MCP was substantiated by determining and ensuring the optimal value of the coefficient of displacement of aggregate grains by cement paste m opt = 1.89 with the inclusion of dusty fractions of the aggregate. The optimal composition of EFC Aggregate : Cement : Water = (3–3.15):1:0.5 with mandatory use of superplasticizer additive to ensure W/C = 0.5 was determined and experimentally confirmed. The dependences of compressive and tensile strength of EFC on: type and content of superplasticizer additives were experimentally investigated; ratio of aggregate content to cement content; microsilica content; pressing pressure. It was established that the maximum strength of EFC is achieved in the case of the use of superplasticizers: polycarboxylate 1.5 % or sulfonaphthalinformaldehyde 1 % by weight of cement. It was also established that with the same A:C = 3:1 and W/C = 0.5, the strength of EFC on the waste of Poltava MCP exceeds the strength of fine-grained concrete on natural, especially fine-grained sand: in compression - by 2 times, in tension - by 1.9 times and reaches 35 MPa at the age of 28 days. The addition of microsilica in the amount of up to 15 % of the mass of cement allows to further increase the compressive strength by 44 %, and the tensile strength by 20 %. It is proposed to form EFC products by layer-by-layer pressing with a layer thickness of 5 mm. It was experimentally established that the maximum strength is achieved at a pressing pressure of 12 MPa.

Experimental studies of the influence of electric potentials on the intensity of corrosion processes in reinforced concrete structures of under-rail foundations have been conducted.A research methodology has been developed that involves the creation of these influences on models and the assessment of their consequences. The effects of capillary rise, evaporation, diffusion, crystallization of salts, electric potential have been created, and the impact of electric potential on the acceleration of transfer processes and manifestations of corrosion signs has been estimated.Models and experimental installations were made, research was conducted. The exposure of the models was carried out in an aqueous environment and in a sodium chloride solution without electrical influence (as a control) and under the influence of a pulsating unidirectional electric potential of the PUEP. It was established that the current through the models decreases under the influence of PUEP, and the specific electrical resistance of the models increases. PUEP accelerates the penetration of ions into the model by 4.43 times, and also causes stronger manifestations of signs of electrocorrosion of the armature. As a result of the exposure of the models without electrical influence in the water environment, weak corrosion of the armature outlets was noted, no corrosion of the armature was observed inside the model; in the sodium chloride solution, strong corrosion of the armature outlets and weak corrosion inside the model was observed. As a result of the influence of PUEP in the water environment, weak corrosion of the fittings was observed, inside the model, no corrosion of the fittings was observed; in the sodium chloride solution, weak corrosion of the armature outlets and strong corrosion was observed inside the model. It has been confirmed that the influence of PUEP significantly accelerates the transfer of ions in concrete and intensifies the corrosion processes of reinforcement. Acceleration of ion transport should also accelerate corrosion processes in concrete, but it is advisable to conduct their research with longer exposure periods of models and with the use of physicochemical methods. Means of draining the currents flowing from the rails through the sleepers were recommended and it was suggested to eliminate the armature discharges from their ends. Проведено експериментальні дослідження впливу електричних потенціалів на інтенсивність корозійних процесів у залізобетонних конструкціях підрейкових основ.Розроблено методику досліджень, яка передбачає створення цих впливів на моделі, та оцінювання їхніх наслідків. Створено впливи капілярного підняття, випаровування, дифузії, кристалізації солей, електричного потенціалу, передбачено оцінювання впливу електричного потенціалу на прискорення процесів перенесення та проявів ознак корозії. Виготовлено моделі та експериментальні установки, проведено дослідження. Експозицію моделей здійснювали у водному середовищі та розчині хлориду натрію без електричного впливу (як контроль) і під впливом пульсуючого однонаправленого електричного потенціалу (ПОЕП). Встановлено, що під час впливу ПОЕП сила струму крізь моделі знижується, питомий електричний опір моделей зростає. ПОЕП прискорює проникнення іонів у модель у 4,43 раза, а також обумовлює більш сильні прояви ознак електрокорозії арматури. Прискорення перенесення іонів має прискорювати й корозійні процеси в бетоні, але їхнє дослідження доцільно проводити з більшими термінами експозиції моделей і з застосуванням фізико-хімічних методів. Рекомендовано засоби дренування струмів, що стікають із рейок крізь шпали, і запропоновано усунути випуски арматури з їхніх торців.