Peculiarities of structural characteristics of modified concrete cement system at the early stages of hardening

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.