Structure Formation Of Cement Stone Research Articles

Comparison of the influence of the type of acidic environment on the properties of acid-resistant alkali-activated cements

The article is devoted to the study of acid resistance of materials developed on the basis of hybrid alkali-activated cements and includes the results obtained during previous studies focused in this direction. This directly concerns the composite compositions of the received cements.The relevance of the research is ensured by the need of the world market of building materials for modern, effective materials that will retain high acid resistance indicators along with increased physical, mechanical and technological characteristics. After all, as is known, traditional acid-resistant cements based on liquid potassium and sodium glass, although they provide appropriate values of resistance to the influence of an acidic environment, are extremely sensitive to the influence of water, which greatly reduces their service life. And materials based on Portland cement are generally not characterized by acid resistance due to the high content of portlandite (Ca(OH)2), highly basic calcium hydrosilicates and ettringite in the structure of hardened cement stone. That is why alkali-activated systems were chosen as the basis, the experience of working with them confirms the effectiveness of their use in the development of this research area.In the course of this study, a comparative characterization of the influence of the type of aggressive environment on the processes of structure formation of cement stone and the formation of acid-resistant phases is conducted. 5% solutions of hydrochloric (HCl) and nitric (HNO3) acids were used for the study. The obtained results not only confirm the possibility of using such cements in the conditions of an aggressive environment with a low pH, but also reflect the degree and influence of this type of environment on the material made according to the presented compositions. Thus, the compressive strength of the samples made according to these tested compositions after 90 days of exposure in hydrochloric and nitric acid solutions ranges from 43.1 MPa to 45.7 MPa and from 47.1 MPa to 49.7 MPa, respectively.

Increasing the Hydration Activity of Tricalcium Silicate by Adding Microdispersed Ettringite as a Nucleating Agent.

Tricalcium silicate (C3S) as a binder material has a decisive influence on the processes of hardening and strength gain of cements and concretes. One of the promising directions is the introduction of dispersed additives into cement mixtures, which allow micro-level control of the composition of hydration products and change the dynamics of the structure formation of cement stone. In this paper, the effect of a microdisperse ettringite additive on the kinetics of the hydration and hardening process of tricalcium silicate was studied. It was shown that ettringite crystals selectively adsorb Ca2+ and OH- ions from a saturated solution of calcium hydroxide, which contributes to the formation of hydrosilicate nuclei on their surface during cement hydration. Hydration of C3S in the presence of ettringite proceeds more intensively; the addition of ettringite contributes to an increase in the content of calcium hydrosilicates in hydration products at the initial stage of the process. Addition of 10 wt.% ettringite to C3S reduces the induction period of the beginning of the main phase of heat release by around two times and increases the amount of heat released on the 1st day of hydration by 15% compared to the control sample. According to electron microscopy data, it was found that during the first hours of hydration of modified C3S, a significant number of nuclei of fibrous particles of calcium hydrosilicates with sizes of 0.2-2 microns were formed on the surface of ettringite crystals. According to the results of kinetic modeling of the setting process of cement pastes using the Avrami-Erofeyev model, it was shown that in the presence of the addition of microcrystals of ettringite, the setting rate is characterized by a slowdown in nucleation, whereas for a sample without an additive, this process proceeds with an acceleration of the formation of solid-phase nuclei. Based on the comparison of kinetic results and mechanical measurements, it is concluded that needle crystals of ettringite during C3S hydration and cement stone hardening are preformed centers for the growth of hydrosilicate nuclei, and they also act as a reinforcing filler, increasing the bending strength of modified samples. The results of the work can be used in practice in the development of methods for controlling the processes of hydration and hardening of cements, as well as for controllable structure formation of cement stone which is important in particular for 3D printing of building products and constructions.

The Role of Water and Aqueous Solutions in the Formation of Induction Periods of Hydration and Structure Formation of Cement Stone

The Role of Water and Aqueous Solutions in the Formation of Induction Periods of Hydration and Structure Formation of Cement Stone

Change in the strength properties of modified concrete over time

To date, there is no data on the change in the strength of hyper - compacted concrete. The conducted field observations summarize the data of a long-term period and allow us to draw a number of conclusions. As shown by numerous studies, the nature of the development of the strength of concrete over time depends mainly on the type of cement, the composition of the concrete mixture, the temperature and humidity conditions of hardening, and also on many other factors. Obtaining highly efficient building materials is possible by modifying the structure of cement stone and concrete. Consequently, the modification of the concrete structure in this direction is intended to improve the technological properties of the material. By modifying it is possible to change the kinetics of the growth of physical properties and the final values of the strength of concrete. Without considering the physico-analytical mechanism for changing the structure formation of concrete, we note that it is primarily aimed at reducing the amount of water - a mixing agent per unit volume of the material. However, various studies have shown that in the initial period, the structure formation of cement stone develops in the optimal direction only at certain volumetric water content. The limiting reduction in water content complicates the process of hydration of the binder, limiting the final strength properties of the material. At the same time, the final strength properties of the material are improved by reducing the volumetric water content of the mixture in every possible way. In all cases, the modification of concrete assumes its composition to be unchanged from the mixing of the mixture to the final stage of the formation of the concrete structure.

THE ROLE OF THE MIXING LIQUID IN THE PROCESSES OF HYDRATION AND HARDENING OF CEMENT STONE

The paper shows that the activation of the mixing fluid by an alternating electromagnetic field of a given signal shape with an energy even a billion times less than the thermal motion energy leads to an increase in the strength of the cement stone hardening structures. As follows from the ultraviolet absorption spectra of the mixing liquid, after repeated treatment with a magnetic field, an increase in the optical density of hydrogen bonds is observed. Thermophysical and acoustic methods have established the inhomogeneity of the temperature distribution at various points of a given volume of water and the formation of spatial structures on its surface at certain frequencies. A wide range of electrophysical methods shows the correlation of changes in the properties of water and the characteristics of the processes of hydration and structure formation of cement stone.

The Influence of Physical Activation of Portland Cement in the Electromagnetic Vortex Layer on the Structure Formation of Cement Stone: The Effect of Extended Storage Period and Carbon Nanotubes Modification

The article presents research of the influence of the electromagnetic vortex layer on the structure formation of cement stone during the activation of portland cement, both without additives and with carbon nanotubes modification. It has been shown that the storage of portland cement powders in open air for 60 days after activation in the electromagnetic mill leads to partial carbonization, wherein the role in absorption reducing of the super plasticizer additive is increased since there is more uniformly localization of the additive on the surface of the portland cement particles. The processing of portland cement in the electromagnetic mill leads to the physical activation of portland cement, which is accompanied by an increase in the amount of heat generated by the hydration of portland cement and the rate of hydration. Thus, the rate of hydration of compositions activated in the electromagnetic mill isincreased 1.615 times at the temperature of the thermostat 22 °C; 1.85 times at 40 °C; 2.71 times at 60 °C; 2.3 times at 80 °C. The modification of cement stonewith carbon nanotubes, which was obtained from portland cement activated in an electromagnetic mill, leads to a higher quantity of silicate phase of portland cement (by 12–39%), as confirmed by a decrease in the number of portlandite in these compositions by 8% in comparison with control composition.

The Structural Formation of Cement Stone Modified by a Solution of Superabsorbent Polymer

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.

Особенности химического состава гидросиликатов бария, полученных по различным технологиям

The article considers the procedural factor effect on the chemical composition of barium hydrosilicates used to control the structure formation of cement stone. It is established that the initial characteristics of sodium hydrosilicate solutions (liquid glass) can influence the carbonation of the deposition product. It has been revealed that during prolonged washing of the deposition products of liquid glasses (barium hydrosilicates), their chemical composition does not change. Concentrations of solutions for synthesis also have an effect on carbonation - so, the use of low-concentration salt solutions increases the content of barium carbonate in the product. It is proposed to study the chemical composition by FTIR spectroscopy method only for powders of deposition products subjected to temperature treatment at a temperature of 800 °C for 60 minutes.The results of the study can be used to control the quality of hydrosilicate additives used at producing composite mineral binders.

The effect of a complex additive on the structure formation of cement stone in conditions of dry hot climate and saline soils

In DHC and saline soils and groundwater conditions, the cement mix quickly loses its mobility and workability. In this regard, it is necessary to plasticize it by introducing various surfactants. However, the surfactant additive used should not slow down the process of hydration and hardening. To ensure salt resistance, it is necessary to increase the density and the strength of concrete. The proposed complex additive was obtained by joint grinding in a ball mill of a soda-sulfate alloy (SSA) and gossypol resin (GR) to a specific surface area of 2800 cm2/g at the rate of 05, -1.5%, and 0.1-0.3%, respectively, of the cement mass. The complex additive was introduced into the mixing water of the cement mix. From the research results obtained, it is seen that with an increase in the content of GR from 0.1 to 0.3%, the normal density decreases by 1.4-4 points, and the setting time (due to the accelerating action of the SSA) decreases at the beginning by 20-50 minutes, and at the end by 60-240 minutes. In 28 days, the control cement gained the strength of 56 MPa, and with a complex addition - 60-68 MPa. The introduction of a complex additive led to an increase in the salt resistance coefficient in the reference cement up to 0.55-0.65, and in the cement with a complex additive up to 0.80-0.86; an increase was observed due to the strength and density of the samples. By increasing the strength, it is possible to save 17-21% of cement.

Specifics of Structure Formation of Cement Stone with Silica Raw Material - A Substrate of Photocatalytic Composite Material

The increasing urbanization of urban areas poses the challenge of the development of materials capable of self-cleaning from organic pollutants formed. Previous papers substantiated the possibility of the coating of titanium oxide as the main agent of the photocatalytic method of cleaning structural materials on silica raw materials in order to increase the degree of its distribution in the volume of cement matrix and, as a result, increase its efficiency.It is obvious that a silica substrate will affect the processes of structure formation during hardening of a cement matrix. During the research, the processes of phase transformations of cement stone modified with silica raw materials of natural and technogenic origin were studied. As a result, the influence of siliceous modifiers on the strength characteristics of the cement stone was determined, which allowed ranking them according to the degree of decrease in efficiency as follows: technogenic raw materials; natural raw materials of silicate composition; natural raw materials of aluminosilicate composition. Quantitative assessments of the degree of efficiency showed the irrationality of using aluminosilicate composition as a silica modifier of natural raw materials, which is explained by its low pozzolanic activity.

Heavyweight Concrete Based on Hydromechanochemically Activated Binder

The results of the influence hydromechanochemical activation of the cement with superplasticizing admixtures, both individually and jointly, on the structure formation of cement stone, the physical and technical properties of heavyweight concrete. An analysis of the microstructure and chemical elements in the spectrum of the surface of a cement stone prepared with preliminary hydromechanochemical activation of the binder with superplasticizing admixtures is presented. The method of hydromechanochemical activation of cement with a superplasticizing admixtures can be recommended for the production of quick-hardening concrete and mortars. The production of quick-hardening concrete is especially important: monolithic concreting in winter, when it is necessary to gain critical strength in concrete in a short time; precast concrete production at precast concrete plants, where it is possible to reduce energy costs for steaming products; modern additive printing technologies using a 3D building printer, requiring the development of new effective quick-hardening mortars and concrete.

Theoretical foundations of the structure formation of cement stone and concrete

The analysis of resource-saving technologies led to the main conclusion that up to now high-intensity methods for physical modification and hyper-consolidation of concrete mix and concrete have not been developed. Taking into account the physicochemical principles of the structure formation of cement stone and concrete, the production of particularly high-strength concrete (Kb q> 100 MPa) is possible by using methods of modifying the concrete mixture, hyper-consolidation of the molded concrete taking into account the development of the optimal structure of the material, capable of significant stretch perception. The implementation of this idea in industrial production, apparently, is possible using simple technological methods for preparing concrete mixture, forming axisymmetric products, methods of hyper-consolidation of molded concrete and physical modification of concrete mixture, for example, by squeezing excess mixing water and entrained air [1].

Ultrasonic modifications of fine-grained limestone concrete

The structure formation of cement stone of fine-grained limestone concrete during hydration hardening of cements and filler based on them occurs due to the development of polydisperse and polymineral conglomerate, a process associated with an increase in the volume of crystallohydrates in relation to the volume of the original cement minerals, mixed with water. Structure formation is accompanied by the process of compaction of the developing system and polycrystallization with the formation of floccules of a porous hydrating mass. In the paper, ultrasonic processing is viewed to accelerate the all- side process of modification of concrete structure and hardening thereby stipulating the growth of strength and durability of concrete.

Regulation of the Properties of Construction Composites Depending on the Material Composition

This paper is devoted to research of directional regulation possibility of the properties of a composite based on the Portland cement by using limestone waste. It is shown that the introduction of limestone waste contributes to changing the nature of crystallization and structure formation of cement stone. With the introduction of limestone waste, in the amount of 15 % by weight of cement, it is possible to obtain the compositions of the class not less than B25-B35.

Study Of Structure Formation Of Organic-Mineral Compositions With Fibrous Filler By Electron Microscopy Method

The article presents the study of processes of structure formation of cement stone and products of hardening of organic-mineral compositions with fibrous filler (shavings) by the electronic scanning microscopy method. It is established that the additive-free cement stone at the age of 28 days has a dense and homogeneous structure, consists of calcium hydro-silicates, Portlandite and calcite - newgrowths characteristic for cement systems. Cellulose fibers, which make up the bulk of the substance of shavings, are sufficiently active, which determines the high adhesion of the hydration products of the cement binder to their surface. It is shown that the introduction of shavings into the organo-mineral composition leads to inhibition of cement hydration processes. Organo-mineral compositions with different shavings content (two compositions) were analyzed. The first composition is characterized by a fairly dense structure, the cement stone consists of globular nanoscale nuclei of hydrosilicates, Portlandite and calcite. The second composition has a loose porous structure, cement stone consists of non-hydrated cement grains, newgrowths are represented by calcite and vaterite. The structure of the contact zone "osprey fiber-cement stone" in the organo-mineral composition of the first composition indicates a good adhesion of the filler surface with the phases of hydrated cement. The use of shavings as a fibrous filler (the first composition) increases the tensile and bending strength, as well as the wear resistance of organo-mineral compositions. The data obtained by scanning electron microscopy are confirmed by the results of studying the processes of structure formation of cement stone by quantitative x-ray phase analysis.

Influence Of Composition Of A Liquid Phase At Hardening Of Cements

The processes of structure formation of cement stone are considered. The change in the composition of the liquid phase and change in the hydration of polymineral cement over time are studied; the change in the concentration of ions of calcium in the course of cement hydration is determined. The effect of calcium chloride and sodium nitrite additives on the composition of the liquid phase during hydration of polymineral cements was investigated. It is shown that these additives significantly increase the metastable concentrations of calcium ions in the liquid phase of hydrating cements, differently affect the amount of supersaturation of the liquid phase and create different conditions for hydrate formation. The determining role of tricalcium silicate in the character of changes in the composition of the liquid phase and the conditions of subsequent hydrate formation during hardening of polymineral cements has been established. High concentrations of calcium ions in the liquid phase cause the removal of the hydrate formation zone from the surface of the initial cement grains into the volume of the intergranular space, which increases the uniformity of the distribution of the solid component in the volume of the cement stone.

INFLUENCE OF THE SCOPE ADDITION ON THE STRUCTURE FORMATION OF THE CEMENT STONE BY THE METHOD OF QUANTITATIVE X-RAY PHASE ANALYSIS

Introduction. The processes of structure formation of cement compositions and the development of effective technologies of building materials is an urgent task for building material science. The use of large-scale man-made product of pulp and paper enterprises – osprey as a fibrous filler in organic and mineral compositions is the successful decision of the problem. The paper analyzes the ways of using osprey in the building materials’ production. The aim of the research is to study the osprey influence on the processes of structure formation of cement stone by quantitative x-ray phase analysis.Materials and methods. The organic and mineral compositions were obtained on the basis of portland cement and osprey. The authors studied the compositions’ phase of osprey, portland cement and the processes of cement stone structure formation in organ and mineral compositions by quantitative x-ray phase analysis.Results. The authors determined the compositions’ phase of mineral impurities of osprey, cellulose, cement, cement stone, organic and mineral compositions and two compositions containing 25 and 75% by weight.Discussion and conclusions. The osprey application as a filler in the organic and mineral composition causes inhibition of processes of cement hydration. The presence of osprey in the hardening organic and mineral composition leads to a change in the composition and structure of the cement stone in comparison with the phase composition of the cement stone without additives. The result of these changes is a significant increase in the amount of calcite, waterite and a significant decrease in the amount of portland. The authors establish that the effective joint work of the reinforcing component of the osprey with the cement matrix is possible with a limited amount of osprey in organic and mineral compositions.

Composite Binders for Concretes with Improved Impact Endurance

The chemical engineering principles of optimization of the physical and mechanical properties and performance characteristics of dispersed reinforced composite materials are proposed which consist in the integrated effect of a composite binder consisting of jointly ground Portland cement, rice husk ash, a complex of inert fillers, and a hyperplasticizer on the processes of structure formation of cement stone. Here, the effect of increasing the impact endurance increases up to sixfold. It is found that dispersed reinforced concretes with an increased ratio of static tensile strength to static compressive strength Rtens/Rcompr and ductility possess the best endurance to dynamic action. It is proved that this ratio can be increased by using dispersed reinforcement of concretes (so-called fibrous concretes). In experimental studies on penetration of both unreinforced and fiber-reinforced concrete slabs, it is noted that samples of unreinforced concrete are completely fractured into large and small pieces, while samples of fiber-reinforced concrete are not completely fractured, and only through penetration at the impact site was observed; that is, fibrous concrete possesses better impact resistance. These results can be applied to the design of various special structures, such as defense structures of civil defense and emergency situations, fortifications of the Russian Ministry of Defense, and concrete structures of nuclear power plants.

Properties of cement stone structure depending on the dispersion of calcium sulfoaluminate

Effect of expanding aluminate hardening additives dispersity on formation of cement stone structure is studied. It is shown that the greatest expansion effect in combination with stone high strength is due to 4CaO3Al2O3CaOSiO2 mineral fractions of 45-63 μm in size. Large crystals of ettringite are gradually formed in hardening stone, when finely ground component of Portland cement becomes highly strong due to its rapid hydration. Under these circumstances, ettringite crystallization results in system expansion.

Investigation into effect of metakaolin-based additives incorporation on formation of cement stone structure

The paper presents studies on the evaluation of the effect of complex additives, including metakaolin, microsilica and superplasticizer on the formation of the phase composition of cement stone. The change in the structure of the modified cement stone was studied and the dependencies were established. A comparative analysis of two complex additives to evaluate the effect of metakaolin on the change in the phase composition of cement stone was carried out. The possibility of obtaining high-performance concrete with low porosity, high early and vintage strength, durability, using additive accelerators and structure modifiers has been investigated. It is established that the use of metakaolin leads to the formation of a cement stone structure, mainly consisting of metastable calcium hydroalumates. It is necessary to use metakaolin together with microsilica and superplasticizer to create a dense structure of cement stone with low capillary porosity from stable low-basic weakly crystallized hydrate phases that are stable when the medium pH is changed.