Structure Of Cement Stone Research Articles

Strength and structure of cement stone exposed to domestic chicken coop

The paper deals with two types of corrosion at the enterprises of the agro-industrial complex: chemical (induced by periodic measures for premises sanitization) and biological (through favorable for the metabolism of microorganisms enviromnent). There are the results of full-scale tests of cement stone in the conditions of a domestic chicken coop without taking measures to clean and disinfect the premises during the period of 11 months. The authors showed changes in the microstructural features of the cement stone and strength characteristics, depending on the area of operation (I – aerial; II – floor with hay and wood chips; III – poultry excrements). On the surface of the samples kept in each zone, the growth of mycelium was not detected. Zone III had the greatest negative effect on strength characteristics of cement stone, particulary 10 % decrease in strength compared to the control, while the microstructure of samples had no new formations of second generation and the presence of dissolution structures. The increase in strength by 25 % in zone II with respect to zone III is explained by the presence of a wet litter contributing to the calmatation of the cement pores and the filling of microcracks in matrix structure. It was found that the smallest external and strength changes were in cement samples exposed in the zone I.

Improvement of the modified heavy concrete properties based on the use of activated silica fume

This article deals with the use of silica fume and ways of its activation to modify the structure of cement stone and concrete on its basis. With regard to any type of filler, namely silica fume, questions that are relevant: how to enter and how many, what mechanisms are involved in the process of structure formation, how much it costs achieved by the effect of modifying the structure and others. Formation of the answers to these questions require a systematic approach to vision problems. Therefore the role of microdispersed fillers in the modification process of the cement stone and concrete structures based on it must be considered together with other sized inclusions at different scale levels. The technology of synthesis of the complex additive based on ultrafine microsilica and superplasticizer “Plastilit RK” with characteristics allowing to use it as an effective additive in concrete has been developed. Studies have confirmed the effect of micro-silica fume in an acid medium (pH=2.1), enriched with oxonium H3O + ions, oxonium cations provide H+, and in an alkaline medium (pH=10-11), enriched with hydroxyl groups OH– - anions OH-, with obtaining dimers of orthosilicic acid Si (OH)4. It was shown that orthosilicic acid particles formed during the chemical dispersion of silica fume are additional crystallization centers, which allows speeding up the process of cement hydration.

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.

Dependence of the Structure of Cement Stone from the Dispersion of the Alumina Component

Usually, sulfoaluminate clinker or a mixture of aluminate clinker with calcium sulphates is used to obtain expansive cements. For these cements ettringite is an important hydration product. This paper deals with the composition and properties of solid solution of calcium aluminate. It was studied an influence of calcium aluminate on structure and properties cement phases. The properties of cements containing these phase were also studied. The investigation of hydration and properties of aluminate cements shows that ettringite and its analogies are formed thus providing expansion and compression of cement stone.

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.

X-Ray Phase Analysis of High-Aluminate Cements under Conditions of early Compression

Study of the structure of cementitious composites under conditions of early-age compression is essential for development of measures to improve their response to mechanical and physical impact at the earliest stage of hardening. The article considers the influence of early-age compression on the structure of high-aluminate cement which has been studied using X-ray phase analysis. Concrete mixes with different water-cement ratio have been designated as targets for research. It has been established that the age of the cement to the moment of load application impacts on composition of formed hydrates, as well as on amorphousness of the structure of high-alumina cement stone. Compression at a very early age leads to an increase in the number of peaks related to hexagonal hydroaluminates and aluminum hydroxide. Load impact results in various recrystallization behaviors. Transformation of hexagonal hydroaluminates into cubical ones is proceeding faster with growth of water-cement ratio in the samples under compression. This is illustrated by an increase of a number of related peaks in X-ray patterns. Notation: C=CaO; A=Al2O3; H=H2O; S=SiO2; M=MgO.

The Topology Structure of Cement Stone with the Use of Compounding Additive Based on Amorphous Aluminosilicates

Proved the possibility of using amorphous aluminosilicate as a modifying agent for the adhesive dry mixes. The presented the technology of preparation of the additive based on amorphous aluminosilicates. Presents data on the influence of additives on the basis of amorphous aluminosilicates change the topological structure of cement stone.

Effect of Waterproofing Penetrating Capillary Mixture on Concrete Waterproofness and Cement Stone Microstructure

Results are provided for a study of concrete waterproofness, structure, and properties of cement stone treated with penetrating water insulation system Penetron. It is shown that formation of waterproofed concrete facilitates formation within cement stone pores of an additional amount of low-basicity calcium hydrosilicate of acicular shape and also calcite.

STRUCTURE CHANGES IN THE REFRACTORY CALCIUM-ALUMINATE CONCRETES

The influence of both the organic and inorganic additives to the calcium aluminates on the cement hydration and the cement stone's structure formation both at the normal and elevated is regarded in the article. The investigating results are given for the phase transformations in the hardened calcium aluminate samples being heated between 20 and 900 °C. The structure change mechanism and the reasons of the cement stone's strength reduction under the high temperature's influence are described. Ill. 3. Ref. 22. Tab. 3.

Phase analysis of the structure of cement stone isolated at its early loading

Phase analysis of the structure of cement stone isolated at its early loading

Application of cementitious composites in mechanical engineering

The paper presents the results of the development of composite fiber-reinforced concrete for use as basic parts of machine-tools and machines. It was revealed that the additions of fly ash and limestone significantly reduce the cracking of concrete. Thus, a clear relationship between the properties of concrete and the features of the structure of cement stone was revealed. The strength and crack resistance of concrete is increased due to an increase in the number of low-basic calcium hydrosilicates, as well as increased gel porosity and reduced capillary porosity (especially at the submicroscopic level).

Modeling of structuring processes at hardening of expanding cements and concretes on their basis

This paper reports the results of experimental research of the effect of strain-restriction conditions on the structure and properties of sulfoaluminate expanding cementitious materials. Theoretical analysis of the development of pattern formation processes is performed by applying the developed rheological model, illustrating features of the kinetics of structure-forming processes according to the ratio of the potential index of extension with linear, flat and volumetric limitation of deformations of the extension. The results show that rheological model adequately correlates with the results of experimental studies and can be described mathematically. Found that with the volume limitation of deformations arising when mixing crystallographic phases with high density and strength, the pore structure of the cement stone contains mainly gel pores. This is the main prerequisite for obtaining a dense, high-strength and durable structure of cement stone and concrete on its basis.

Исследование влияния комплексного модификатора на основе углеродных нанотрубок на процессы структурообразования цементного камня

Исследование влияния комплексного модификатора на основе углеродных нанотрубок на процессы структурообразования цементного камня

Исследование химического состава «летучей» золы и ее влияние на прочность цементного камня

Статья посвящена проблемам, связанным со снижением негативного воздействия золошлаковых отходов ТЭЦ Казахстана на окружающую среду. Вырабатываемая в больших количествах летучая зола как продукт сгорания топлива на энергостанциях отрицательно влияет на внешнюю среду, загрязняя воздух, почвы, сточные воды и т.п. В статье приведены результаты химического состава золошлаковых отходов. Рассмотрены возможные пути использования золы. Также изучен фазовый состав цементного камня с добавлением летучей золы с помощью современных методов анализа: рентгенофазовый и рентгенофлуоресцентный. Было выявлено, что к основным макроэлементам золы относятся Si, Al, Fе, О, Ca, Ti, Mg, S, K, Na. Помимо изучения размеров и форм микросфер в работе ставились задачи определения видов термоактивных фаз, составляющих цементного камня при термообработке; изучение структурных изменений при термообработке. Рентгенофазовый анализ по исследованию зольных микросфер показал следующие фазы: муллита Al6Si2O13, кварца SiO2 и аморфной стеклофазы. Применение золы как источника оксидов алюминия и кремния не только позволит снизить использование невозобновляемых ресурсов, но и получить материалы с улучшенными теплофизическими характеристиками (прочность, термостойкость и теплопроводность). Выбор оптимального количества золы уноса взамен части цемента способствует образованию желательной структуры цементного камня.

Investigation of the structure of cement stone, obtaining and optimization of high-strength concrete on mechanically activated binder

Physico-chemical methods of the study of hydrated cement by mechanically activated binding substance with organo-mineral additive (microsilica + C-3) were presented. It was explored the influence of the additive into the kinetics of formation lowly-basic calcium hydrosilicate. The experiment conducted in accordance with a three-factorial D-optimum plan enabled to establish an influence of blending and technological factors (x1 – content of microsilica in the binder - 5±5%; x2 – binder consumption in concrete - 450±100 kg/m3; x3 – specific area (Ssp) of Portland cement 400±100 m2/kg) on physical and mechanical properties of concrete (compression strength, water absorption). It was established that the use of the mechanically activated blended Portland cement of general purpose with an organomineral additive (microsilica+C-3) makes it possible to obtain high-strength concretes which compression strength on the 28th day reaches 120 MPa. Optimization of concrete mixes was achieved on the basis of obtained mathematical models that reflect the influence of blending and technological factors on physical and mechanical properties of a high-strength concrete.

Use sulfoferritic cements in construction

Currently, high-rise construction has received increasing attention around the world. In the big cities under construction is less space and one solution is the high-rise construction. However, high-rise buildings use special requirements, such as strength, thermal insulation, wind load and others. When concrete is exposed to continuous loads by wind or to mechanical loads, it undergoes abrasion. Resistance to this process depends on the characteristics of materials that the concrete and finishing seams are made of. Research on increasing impact and abrasion resistance of calcium sulfoferrite-based cement stone from the perspective of formation of cement stone structure will be instrumental in developing durable materials for application in high-rise construction.

Influence of Superplasticizer-Microsilica Complex on Cement Hydration, Structure and Properties of Cement Stone

According to the study results, the influence of complex additives based on microsilica and superplasticizers on the processes of the heat release, hydration, hardening, formation of the structure and properties of cement stone was determined. Calorimetry, derivatography, X-ray phase analysis, electronic microscopy and physical-mechanical methods for analyzing the properties of cement stone were used for the studies. It was established that plasticizing additives, in addition to the main water-reducing and rheological functions, regulate cement solidification and hardening while polycarboxylate superplasticizers even contribute to the formation of a special, amorphized microstructure of cement stone. In a complex containing microsilica and a polycarboxylate superplasticizer the strength increases sharply with a sharp drop in the capillary porosity responsible for the density, permeability, durability, and hence, the longevity of concrete. All this is a weighty argument in favor of the use of microsilica jointly with a polycarboxylate superplasticizer in road concretes operated under aggressive conditions.

Structuring in Cement Systems with Introduction of Graphene Nano-Additives

At present, one of the most promising areas in the field of concrete research is the study of the effect of nano-additives for the production of highly effective concretes. Many authors have already obtained primary results which testify to the very effective role of nanoadditives based on carbon in modifying concrete. In this paper, the influence of a nano-additive of graphene on the phase composition and microstructure of the cement stone was studied. It has been found that, when a nano-additive of graphene is introduced, low-basic calcium hydrosilicates are mainly formed. This leads to an increase in the compressive strength of concrete. The results of the study of the microstructure of cement stone with nano-additive graphene showed that the high compressive strength of concrete modified with nano-additive graphene is explained by the cement stone dense structure. Thus, it was found that the nanoadditive of graphene contributes to the formation of a dense structure of cement stone, composed mainly of low-basic calcium hydrosilicates, and due to this, the physical and mechanical characteristics of concrete and its resistance to frost and other forms of aggression.

Structure and Properties of Concrete for Injection with Two-Stage Expansion

Often, when it is necessary to fill formwork space in confined working conditions with limited operational control in some engineering solutions the special materials for injection are used. In this case, it is advisable to use high-fluidity concrete mixes made with К-cement, regulator of the kinetics of structure formation, superplasticizer and gas-forming admixture. The gas-forming admixture obtains of expansion of fresh-concrete during first stage. The special sulfo-alumina additive in K-cement obtains of expansion of hardening concrete during second stage. The main regularities in the formation of the structure and properties of cement stone are considered. The dependences "composition-technology-structure-properties" for concretes with two-stage expansion are clarified. The main provisions for determination of mix proportion for concrete are proposed. The quantitative relationships between the construction properties of concretes and prescription and technological factors are obtained.

Effect of calcium and magnesium oxides on the properties of expanding cements and plugging mortars

Plugging expanding cements ensure a better quality of insulation of productive oil and gas-containing layers from aquifers. We examined the effect of additives in the oxide form of expansion on the physical-mechanical properties of cements and plugging mortars. It was established that the introduction of calcium oxide and magnesium oxide additives in the amount of 20 % by weight leads to an increase, respectively, by 20 ‒ 40 % and 12 ‒ 36 % in cement water consumption, and reduces by 20 ‒ 32 % and 52 ‒ 64 % strength of the cements with additives in comparison with additive-free cement. It should be noted that the introduction of a magnesium oxide additive results in a more significant reduction of cement strength (by 40–47 %) and plugging mortars strength (by 29–44 %) in comparison with the samples with a calcium oxide additive. Cements and plugging mortars with a calcium oxide additive yield a much greater increase (by almost three times) in the dimensions of samples than a magnesium oxide additive. The negative impact of magnesium oxide on the strength of cements and plugging mortars can be explained by the features of hydration products of this additive. Magnesium hydroxide is formed in the form of fibers and flakes and it does not consequently participate in the formation of crystalline structure of cement stone. At the same time, calcium hydroxide can, in the process of hydration, form calcium hydrosilicates and portlandite, which somewhat reduces the negative effect of this additive on the strength of cements and plugging mortars. In addition, with an increase in temperature, based on data from electron microscopic analysis, there occurs the formation of a larger mass of magnesium hydroxide due to the formation of smaller fibers instead of the large lamellar ones. The total weight of new formations increases ‒ the expansion of the hardening mass of the plugging mortar also grows. However, these new formations of magnesium hydroxide do not possess strength and, in general, cement stone essentially loses strength compared to the cement stone with a calcium oxide additive. This confirms inappropriateness of using magnesium oxide as the additive in the production of expanding plugging cements.