Papers by Keyword: Hydration

Abstract: Experimental studies of some physical properties of paulownia wood and identifies differences in comparison with other popular species are presented. In particular, the regularities of hydration and dehydration processes were investigated. Based on the results obtained, reliable data on the hygroscopic properties of paulownia were obtained for the first time. It was found that the hydration rapidity of paulownia (V_pl = 1.493) exceeds the similar rate of pine (V_pn = 1.1313) at a temperature of 20 °C. Changing the temperature of the liquid in which the wood is modified leads to an increase in the impregnation rapidity and, therefore, increases the productivity of the process. The dehydration rapidity of both species is almost the same (k = –0.002), which allows them to be dried simultaneously in the same chamber, optimizing production logistics. The dependence of liquid absorption on concentration was investigated. It has been found that a higher concentration outside causes a greater diffusion flux into the sample, while a higher concentration inside leads to a decrease in the sample weight. During the hydration stage, the weight of paulownia samples increased by 4 times, and pine samples – by 2.5 times. A two-stage kinetic model of wood hydration has been developed, which adequately describes the dynamics of the process. The resulting S-shaped curve clearly characterizes the features of the kinetics processes with saturation. Verification showed a high correlation – 85 % – for hydration and over 90 % for dehydration, which allows for accurate modeling and prediction of the technological processes of wood impregnation and drying.

Abstract: The paper discusses the results of studying the hardening process of a gypsum-based composite material using a thermal imager. Thermal imaging research involves periodically obtaining thermal images of hardening material with pronounced hydration exotherm. It is assumed that the intensity of hydration and heat release depend on the state of the heterogeneous system, the structure of the forming material and the degree of aggregation of particles of hydrating components. The resulting images contain both visible and hidden information about the physical and chemical processes occurring in the material. To fully obtain such information, computer image processing methods were used. Intensity histograms were constructed and analyzed, for which regular changes were observed in the process of structure formation. As a generalization of the observed patterns, a working hypothesis is proposed about the filling of scales of physicochemical characteristics and, in particular, large-scale structural scales, in the process of structure formation. An image processing algorithm has been developed that makes it possible to construct isothermal cells‒areas of material with the same temperature. The geometric characteristics of the resulting areas, forming a partition of the study area, were studied by an automated method and reflected using histograms. The interpretation of the influence of a changing temperature distribution on the properties of a material is based on the idea of an approximate correspondence between a network of temperature cells and a Voronoi network that defines regions of a disordered structure. The spatiotemporal features of thermal processes are considered, indicating a possible decrease in the strength characteristics of the material.

Abstract: This study investigates the impact of electrolyte concentration on the electrochemical behavior of copper hexacyanoferrate (CuHCF), a promising active material for aqueous zinc-ion battery electrodes. Cyclic voltammetry, charge-discharge measurements, and X-ray diffraction analysis were employed to assess the electrochemical reactions and structural integrity of the CuHCF electrode under varying electrolyte concentrations. The results revealed a significant influence of electrolyte concentration on the electrochemical performance of the CuHCF electrode. Specifically, the charge-discharge capacity exhibited an initial increase as the electrolyte concentration increased from 1.0 to 2.0 mol dm^‒3, followed by a subsequent decrease. This decrease in capacity was attributed to the occurrence of an electrode/electrolyte interfacial reaction in the low-potential region of 0.0–0.3 V, coupled with structural changes in the CuHCF active material. Notably, these findings underscore the strong correlation between the electrochemical performance of the CuHCF electrode and the hydration structure of zinc ions, as well as the pH of the electrolyte solution. Thus, optimizing the electrolyte composition holds significant potential for enhancing the performance of aqueous zinc-ion batteries employing CuHCF electrodes.

Abstract: In this article in order to verify the probability of the formation of the compound CaBaAl₄O₈, a thermodynamic analysis of the following possible solid-phase reactions of its formation was carried out: formation of CaBaAl₄O₈ from the initial components - calcium carbon dioxide, barium carbon dioxide and aluminum oxide; the probability of formation of dual compounds CaAl₂O₄ and BaAl₂O₄ from the same raw materials (since the compound CaBaAl₄O₈ is located on the BaAl₂O₄-CaAl₂O₄ conjugate) and the possibility of formation of the compound CaBaAl₄O₈ from binary compounds CaAl₂O₄ and BaAl₂O₄. As a result of our experimental studies, the existence of ternary compounds Вa₃CaAl₂O₇ and ВaCa₂Al₈O₁₅ was confirmed, and it was found that the Вa₃CaAl₂O₇ compound exists in the system at least up to a temperature of 1400 °C. Thus, our studies have determined an increase in the temperature limits of its existence, in contrast to the data of previous researchers, who indicated 1250 °C as the upper temperature of existence of Вa₃CaAl₂O₇.

Abstract: The use of carboxylic acids in mix design alters the hydration process of cement, the resulting pore structure of the obtained cement paste, and, consequently, the mechanical properties of concrete. All these changes are directly related to the structure of the calcium silicate hydrate phase. In the present study, the effect of acetic acid and oxalic acid on the hydration of Portland-limestone cement was monitored using solid state ²⁹Si NMR spectroscopy. The results showed that acetic acid facilitated alite and belite hydration, however, the formation of polymerized silicate chains, incorporating Q²_p species, begun later than in pure cement paste. Oxalic acid accelerated the polymerization, but slowed down alite and belite hydration. Such behaviors may correspond to decreased porosity (acetic acid addition) and increased strength (oxalic acid addition). Both acids accelerated belite hydration, compared to the pure paste, likely due to an increased acidity of the pore solution. The findings provide structural information about C─S─H phase, to be considered for thaumasite sulfate attack investigations on Portland-limestone cement pastes containing carboxylic acids.

Abstract: The possibility of increasing the basic properties of concrete products by using Portland cement with additions of sulfated clinkers as a binder is considered. It was found that when the binder is hydrated, aluminate and ferruginous ettringite are formed, which reinforce the hardening structure of the stone, increase its strength properties and resistance to the corrosive effect of sulfates.

Abstract: With the development of 3D technologies in construction, the development of formulations that are indifferent to the influence of the environment is in demand. Conditions of intense water loss from cement systems arise during the layer-by-layer printing process. This leads to a decrease in density, high shrinkage, and a decrease in the strength and durability of the composite. The use of superabsorbent polymer (SAP) solutions, in contrast to granules, will provide hardening Portland cement with a water supply for internal care of hydration processes. The aim of the work is to study the effect of SAP solution on the processes of structure formation of cement stone, hardening in unfavorable conditions. In this paper, the features of the structure formation of cement systems in the presence of SAP are established. It is shown that the use of polymer in an amount of no more than 1.5% by the weight of Portland cement provides the formation of a more perfect crystalline structure of the cement stone, which allows for an increase in the degree of cement hydration. When the amount of SAP is ≥ 1.5% by the weight of Portland cement, a decrease in the intensity of the maxima corresponding to hydration products is observed.

Abstract: Hemp concretes are the most widely used biobased concretes in France. However, their growth is still limited by the lack of knowledge and high variability of the performances of biobased concretes, especially for their mechanical properties. These results are related to interactions between the mineral binder and plant compounds that modify the hydration of the cement. In this work, the interactions between cement and eight types of hemp shiv, and a flax shiv are studied by isothermal calorimetry. The setting delays observed in the presence of plants are interpreted by analyzing the molecules extracted from these plants in water. A link can be observed between the setting delay and the coloration of the extract solutions or their concentration in reducing sugars and in polyphenols. These results constitute a basis in the objective to define an indicator enabling to predict the compatibility between plants and mineral binders.

Abstract: Organic admixtures are an indispensable component of modern concrete. Thus, their purposeful application is not only technically and economically viable but in addition an inevitable tool to make concrete more environmentally friendly. In this context, the use of polysaccharides has increasingly gained interest in the built environment as sustainable resource for performance enhancement. However, due to its origin, biopolymers possess a vast variety of molecular structures which can result in incompatibilities with other polymers present in concrete, such as superplasticizers. The present study highlights effects of the joint application of different types of starches and polycarboxylates with respect to their influence on cement hydration and structural build-up of cement pastes.

Abstract: Ordinary Portland cement (OPC) is widely used building material, and its hydration products can be recycling as low-cost absorbents. The loading of iron oxide is helpful to further improve their adsorption performance. In view of the fact that green rusts are frequently occurrence intermediate products in the co-precipitation of iron salt and prone to be oxidized into stable iron minerals. This study simulated co-precipitation to carry out iron-modification on hydration OPC. The results demonstrate that as the carrier materials, hydration OPC behaves excellent affinity with green rusts. Under the conditions of high temperature (70 oC) and high alklinity (pH=11), green rusts mainly transformed into feroxydrate, and a minor part are into magnetite. The enrichment and transformation of green rust can be regarded as an efficient approach for immobilization of iron oxide (oxyhydroxide).