Browsing by Author "Rudenko, Dmytro V."

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Peculiarities of Structural Characteristics of Modified Concrete Cement System at the Early Stages of Hardening
(Придніпровська державна академія будівництва та архітектури, 2019) Pshinko, Oleksandr M.; Rudenko, Dmytro V.
EN: Abstract. Purpose. Determination of the types of bonds formed in the modified concrete cement matrix and the evaluation of the quality of these bonds in a inhomogeneous material for the determination of geometric and physical relationships between the structure of modifiers and the cement matrix at the early stage of structure formation. Method. Investigation of the processes of hydration and structure formation of conventional and modified cement systems was carried out using X-ray diffraction, differential-thermal and microscopic analyses, and infrared spectroscopy. The analysis of the structural parameters of the cement matrix of concrete was carried out by the method of mercury porosimetry, as well as the adsorption of water and nitrogen vapor. Results. The system of assembling with the corresponding structure is formed during the layout and contact of the mineral components of the cement system and aggregate grains in the process of mixing with water, stirring and placing of concrete mixture. The change in the quantitative characteristics of the structure of modified concrete was observed at the change in the intensity of modification. Observed changes in the morphological structure of the cement matrix cannot be random, as they are confirmed by repeated experiments at reproducibility from 82 to 96 %. At the same time, such a change in the morphology of new formations was not observed in normal concrete. From the given data, a significant increase in the lamellar-prismatic component in the cement matrix of modified concrete is obvious. The number of formed crystalline new formations increases with the increase of curing time. This can be explained by the system approach: the morphology of the structure of the cement matrix − the result of the interaction of systems of assembly and growth. At the same time, the growth system (recrystallization and development of the structure in time) can effectively develop without a sufficiently complete development of the system of assembly (accumulation of primary products of hydration). Scientific novelty. For the first time, the peculiarities of the structured formation of the modified cement system have been established, they consist in the fact that magnesium chloride hydrate crystals grow rapidly in the space between the hydrated new formations of clinker minerals, and as the result, the mechanical bond is responsible for the development of initial strength and stiffness. Since the free growth of crystals is hindered by the lack of space, the crystals mutually germinate, forming a dense structure that causes the growth of strength; it was first established that in a modified hydrated cement system, as a result of the interaction of different macroions, a structure-forming process develops with a predominance of active parts that significantly exceed its dissipative part in comparison with normal cure conditions. The results obtained in modeling the behavior of the modified cement system, which is hydrated, show that the system has fluctuations in the concentration of intermediate products of hydration, identified with the appearance of the spatial-temporal structure. Practical relevance. Physico-chemical modification of the cement system provides a change in the morphotropy of new crystalhydrate formations, which will contribute to the formation of the design properties of concrete.
Properties of Modified Concrete for Special Purpose Structures
(Дніпропетровський національний університет залізничного транспорту ім. акад. В. Лазаряна, Дніпро, 2018) Rudenko, Dmytro V.
EN: Purpose. The paper is aimed at developing the scientific fundamentals of new-generation monolithic concrete technology for special purpose structures by controlling the processes of structure formation of a modified cement system under natural hardening conditions. Methodology. The kinetics of interaction between the cement system and aggregates was evaluated by microcalorimetry. The measurements were carried out continuously for 24 hours after preparation of the mixture. The differential and integral characteristics of the heat release of the solidifying system were recorded. nvestigation of the rheological properties of concrete ixtures was carried out on the mixtures with 10...15 cm consistency. The microhardness of contact layers was investigated on concrete cubes with dimensions from 20×20×20 to 0×50×50 mm. When determining the structural characteristics, x-ray phase and differential-thermal analyzes of the concrete cement matrix were used. Infrared spectroscopy was used to determine the effect of physicochemical modification on the cement system. Tensile creep was studied over a wide load range from 0.2Rt to 0.8Rt. Findings. It is determined that the reason for changing the concrete properties of natural hardening is the change in its ygrometric and thermal state, as well as the harmonic fluctuations of these environmental factors. The hygrometry of concrete depends on the thermal moisture conditions of the environment, the type and composition of concrete, the massiveness of concrete elements. An analysis of these factors and experimental data made it possible to establish the exponential dependence of the change in the hygrometric state of monolithic natural hardening concrete. The change in the moisture state of concrete makes it possible to predict its volumetric deformations. Originality. For the first time, the features of the structure formation of a modified cement system are established, consisting in the fact that magnesium chloride hydrate crystals grow rapidly in the space between hydrated clinker minerals, and the resulting mechanical cohesion defines the development of initial strength and rigidity. Since the free growth of crystals is hampered by a lack of space, the crystals mutually intergrow, forming a dense structure, contributing to the growth of strength. The developed organo-mineral modifying complex provides disperse reinforcement of the cement matrix of concrete. Practical value. The obtained ependences of structural concrete stresses make it possible to analyze their effect on the structure of modified concrete: to determine the probability of formation around the filler particles of the plastic flow zone, the material microcrack formation zone, the crack initiation period, the microcrack onset conditions, and the change of elasticity modulus of the material caused by microcracks in its structure. Disperous modification of cement matrix allows to obtain durable oncrete of special purpose with design operational roperties. The developed binder disperse modification technology, the established features of the structure formation mechanism for the modified cement system, as well as the use of the principle of congruence of a complex of technological influences to the physico-chemical processes of hydration of clinker minerals allowed developing the scientific fundamentals for the special purpose concrete technology. This helps to expand the use of modified concrete in various types of construction.
Research of Operational Properties of Modified Specialized Concrete for Transport Constructions
(EDIS, University of Zilina, Slovakia, 2019) Pshinko, Oleksandr M.; Shcherbak, Andriy S.; Rudenko, Dmytro V.
EN: It was established that the polymeric component of the organomineral modifying complex changes the nature of the super-molecular structures in the activated cement system - at optimal filling, globules decrease in size preventing the phase surface diffusion, which contributes to increase of the waterproofness of modified concrete. When introducing a modified cement system into the concrete mixture, the reduction of the open porosity to 3-5 %, depending on the composition, has been achieved. Conducted tests for water resistance and frost resistance of the repair layer of concrete showed that the modified concrete corresponds to the mark on water resistance W14 and the brand on the frost resistance F300. The developed technology of physico-chemical activation of the cement system allows the use of conventional cement for obtaining durable concrete of special purpose, which allows to reduce the cost of such concrete by 27-34 %.
Study of Rheological Properties of Modified Concrete Mixtures at Vibration
(Trans Tech Publications LTD, Switzerland, 2019) Pshinko, Oleksandr M.; Hromova, Olena V.; Rudenko, Dmytro V.
EN: Abstract: Study of rheological properties of concrete mixtures based on modified cement systems in order to determine process parameters. Methodology. To study structural-mechanical properties of modified concrete mixtures of different consistency at their horizontal vibrating displacement an oscillatory viscometer was designed. Results. The optimization of the process of vibration displacement of concrete mixtures with the specification of parameters of vibration impacts taking into account structural-mechanical properties of the mixture is performed. It has been established that the viscosity of the modified cement system of the concrete mixture is a variable quantity, which depends on the parameters of the vibration impacts. Scientific novelty. The mechanism of interaction of the modified concrete mixture with the form and the table vibrator during its vibration compaction is determined. On the basis of this, a model of concrete laying process control is proposed, that allows to predict the ability to form a dense concrete structure. Practical significance. Disclosed physical nature of the process of vibrating displacement of modified concrete mixtures using the principles of physical-chemical mechanics of concrete allows reasonably choose the best options for vibration impacts.