scholarly journals Modified Light Concrete of High Strength

2018 ◽  
Vol 230 ◽  
pp. 03015
Author(s):  
Katerina Pushkarova ◽  
Kostiantyn Kaverin ◽  
Danilo Gadayuchyk

The study is devoted to the development of increased strength lightweight concrete based on Portland cement modified with a complex organo-siliceous additive containing a polycarboxylate superplasticizer and an active fine-ground siliceous component. The effect of this complex additive on the physical and chemical characteristics of the hydration and structure formation processes was investigated and it was shown that the high kinetics of the strength gain is provided by directional formation of low-basic calcium hydrosilicates, hydrogranates and plazolite, which are crystallo chemically similar to each other, and provide a dense and strength cement stone matrix. Modification by a complex additive makes possible to obtain concrete mixes with S4 consistency while a Portland cement consumption per 1m3 of not more than 330 kg, with a compressive strength of 55 MPa, watertightness up to W8, frost resistance up to F400, corrosion resistance coefficients Kc in the magnesium sulfate, sodium and ammonium solutions by 10 to 24%. The introduction of a complex additive also helps to reduce the relative shrinkage by 16 to 19% compared to the control composition, which has a positive effect on the durability of the resulting concrete.

Author(s):  
N. Gurinenko

В материале статьи приведены результаты исследований влияния на кинетику твердения и свойства тяжелого бетона разрабатываемой полифункциональной комплексной добавки, содержащей пластификатор, ультрадисперсный микрокремнезем (УДМК) и ускоряюще-уплотняющий компонент, с целью повышения темпа роста и уровня прочности бетона на основе формирования более плотной структуры цементного камня и зон его контакта с поверхностью зерен заполнителя. Экспериментально подтверждена эффективность предлагаемой добавки при ее применении как в высокопрочном, так и в рядовом по прочности бетоне с целью повышения темпа и уровня роста прочности, снижения энергетических затрат в технологии производства бетонных и железобетонных изделий и монолитном строительстве, повышения плотности и непроницаемости, а на этой основе качественных характеристик бетона водонепроницаемости, морозостойкости и защитной способности по отношению к стальной арматуре. Показана возможность значительного снижения энергетических затрат на прогрев бетона с полифункциональной комплексной добавкой за счет использования термосного режима его твердения с начальным разогревом до 30...35 С и последующей выдержки в тепловом устройстве без подвода тепла. В этих условиях бетон с полифункциональной комплексной добавкой при прогреве по режиму 2 ч. предварительной выдержки, 2 ч. подъема температуры и 12 ч. выдержки в тепловом устройстве набирает прочность на уровне 80...90 от проектной (28 суточной), что достаточно не только для передачи преднапряжения арматуры на бетон, но и для отпуска изделий потребителю. В исследованиях использовали стандартизованные методики оценки прочности и эксплуатационных свойств бетона.The article presents the results of studies on the kinetics of hardening and the properties of heavy concrete being developed by a multifunctional complex additive containing a plasticizer, ultradispersed microsilica (UDMS) and an accelerating compaction component in order to increase the growth rate and level of concrete strength based on the formation of a more dense cement stone structure and zones of its contact with the surface of the aggregate grains. The effectiveness of the proposed additive was experimentally confirmed in its application both in high-strength and ordinary concrete in terms of strength in order to increase the rate and level of strength growth, reduce energy costs in the production technology of concrete and reinforced concrete products and monolithic construction, increase density and impermeability, and on this basis, the quality characteristics of concrete - water resistance, frost resistance and protective ability in relation to steel reinforcement. The possibility of a significant reduction in energy costs for heating concrete with a multifunctional complex additive is shown, due to the use of the thermos mode of its hardening with initial heating to 35 ... 40 C and subsequent aging in a thermal device without heat supply. Under these conditions, concrete with a multifunctional complex additive during heating according to the mode: 2 hours of preliminary exposure, 2 hours of temperature rise, and 12 hours of exposure in a thermal device gains strength at 80 ... 90 of the design (28 days), which is not only enough for transferring prestressing of reinforcement to concrete, but also for dispensing products to the consumer. The studies used standardized methods for assessing the strength and performance properties of concrete.


2019 ◽  
Vol 974 ◽  
pp. 195-200
Author(s):  
Yury R. Krivoborodov ◽  
Svetlana V. Samchenko

The article presents the results of a study of the effect of synthesized microdisperse additives of crystalline hydrates based on calcium sulfoaluminates on the properties of cement stone. The effectiveness of the use of a rotary pulsation apparatus (RPA) to obtain microdispersed additives is identified. The possibility of accelerating the hardening of cement stone by entering microdispersed additives into its composition is shown. It has been established that in the presence of microdispersed additives of crystalline hydrates in the cement stone, the phase composition of hydrate tumors changes, the amount of calcium hydrosilicates and ettringite increases, the porosity decreases and the strength of the cement stone increases. This provision is confirmed by the increase in the degree of cement hydration, the amount of bound water in all periods of hardening of the stone. It is proposed to use microdisperse additives, which play the role of primers for the crystallization of ettringite and calcium hydrosilicates, to increase the strength of cement stone in the early stages of hardening.


2018 ◽  
Vol 196 ◽  
pp. 04035 ◽  
Author(s):  
Igor Kharchenko ◽  
Alexander Panchenko ◽  
Alexey Kharchenko ◽  
Vyacheslav Alekseev

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.


2013 ◽  
Vol 746 ◽  
pp. 285-288 ◽  
Author(s):  
Evgeniy Valerjevich Korolev ◽  
Alexandr Sergeevich Inozemtcev

The paper presents the results of research aimed at development of nanomodified high-strength lightweight concrete for construction. The developed concretes are of low average density and high ultimate compressive strength. It is shown that to produce this type of concrete one need to use hollow glass and aluminosilicate microspheres. To increase the durability of adhesion between cement stone and fine filler the authors offer to use complex nanodimensional modifier based on iron hydroxide sol and silica sol as a surface nanomodifier for hollow microspheres. It is hypothesized that the proposed modifier has complex effect on the activity of the cement hydration and, at the same time increases bond strength between filler and cement-mineral matrix. The compositions for energy-efficient nanomodified high-strength lightweight concrete which density is 1300...1500 kg/m3 and compressive strength is 40...70 MPa have been developed. The approaches to the design of high-strength lightweight concrete with density of less than 2000 kg/m3are formulated. It is noted that the proposed concretes possess dense homogeneous structure and moderate mobility. Thus, they allow processing by vibration during production. The economic and practical implications for realization of high-strength lightweight concrete in industrial production (in particular, for construction of high-rise buildings) have been justified. The results of industrial testing of new compositions in precast concrete technology are shown.


Author(s):  
K. Strokin ◽  
D. Novikov ◽  
V. Konovalova ◽  
N. Kasiyanenko

The article considers the change in the structural and phase composition of cement stone made of Portland cement of the CEM I 42.5 N brand in the process of bacterial and fungal corrosion during 6 months when humidified. The X-ray images of cement stone show peaks that characterize the non-hydrated components of Portland cement alite, belite, tricalcium aluminate, four-calcium aluminoferrite and gypsum. By the method of X-ray phase analysis, it is found that during microbiological corrosion, the content of all phases of cement stone decreases. The aspergillus niger van Tieghem fungi have a stronger effect on the structural and phase composition of cement stone. Fungal microorganisms destroy the crystalline phases and absorb amorphous phases – calcium hydrosilicates C-S-H (I) and C-S-H (II) and tobermorite. When bacteria Bacillus subtilis affects the cement stone, the content of the calcite phase increases, which is a product of corrosion, while the action of black mold reduces the intensity of CaCO3 peaks. A decrease in the content of low-base calcium hydrosilicates and ettringite, as well as other crystalline phases, leads to a decrease in the compressive strength of the cement stone. During 6 months of microbiological corrosion of cement concrete under conditions of constant wetting, the compressive strength decreases by about 35 %.


2016 ◽  
Vol 683 ◽  
pp. 90-94 ◽  
Author(s):  
Anna Nikolaevna Grishina ◽  
Evgeniy Valerjevich Korolev

The development of new types of composite materials is an important aim for construction. Nanoscale admixtures allow efficient control of the composition and properties. Results of experimental investigations concerning effect of admixture of nanoscale barium hydrosilicates to the chemical composition of hydrated portland cement are discussed in the present work. It is shown that several key processes are taking place during nanomodification. Amount of portlandite in cement stone decreases, and there is also quantity growth of different calcium hydrosilicates CSH (I), CSH (II), riversideite and xonotlite. Influence of composition and storing time of barium hydrosilicates to the ratio of different portland cement hydration products is examined. It is found that admixture of barium hydrosilicates with gross formula BaO•26.47SiO2•nH2O stored for 28 days leads to both reduction of portlandite and accretion of hydrated phase.


2015 ◽  
Vol 14 (1) ◽  
pp. 105-113 ◽  
Author(s):  
Khrystyna Sobol ◽  
Taras Markiv ◽  
Volodymyr Terlyha ◽  
Wojciech Franus

In this study, properties and peculiarities of hydration processes as well as paste microstructure of blended cements containing 10% by weight of natural zeolite were investigated. Free calcium hydroxide content, crystalline hydration products and microstructural architecture of hydrated cement pastes were examined by physical and chemical methods. It was found that the addition of natural zeolite provides formation of an extra amount of fine crystalline ettringite and tobermorite-like calcium hydrosilicates of CSH (B) type in the mineral non-clinker part of Portland cement resulting in strength synthesis of cement stone with high performance properties.


Author(s):  
L. Zagoronyuk ◽  
S. Rahimbaev ◽  
D. Sumskoy ◽  
V. Ryzhikh

The results of studying the processes of hydration of binder compositions obtained at different ratios of cement and waste of expanded perlite sand (from 5 to 10%), in a vortex jet mill, under different modes of mechanical and chemical activation - from one to three passes are presented. Comprehensive studies of hydration products by X-ray phase analysis and electron microscopy indicate that the use of highly dispersed wastes from the production of expanded perlite sand in binding compositions allows an increase in the content of hydrated neoplasms due to an increase in the degree of hydration of the main clinker phases, as well as due to the pozzolanic activity of these wastes. The contact zone between the hydrated compounds and the remnants of the grains of the original cements has a special effect on the formation of a high-strength structure of the cement stone. The structure formation of a cement stone depends on a number of factors, which can be influenced by various technological methods. When designing compositions of cement composites, it is necessary to ensure that hydration products in the created system are present along with low-basic calcium hydrosilicates and high-basic ones. Their ratio should be such that carbonization does not reduce the volume of the formed crystalline phase of the cement stone. The composition of the hydration products determines the level of supersaturation of the solution, the type and number of impurities soluble in water, the duration of the hydration process, etc. The chemistry of the reactions of the hydrated system changes accordingly. It is found that the intensity of the diffraction maxima, indicating the presence of highly basic calcium hydrosilicates in the compositions that underwent mechanical activation, increases by 18% in comparison with the ordinary PC. The strength characteristics of Portland cements, which have undergone mechanical activation, increase up to 15% compared to the original PC. The most rational binder composition is established in terms of composition (No. 6), mechanical activation and maximum compressive strength at 28 days of age – 69.1 MPa.


2019 ◽  
Vol 91 ◽  
pp. 02014
Author(s):  
Dmitriy A. Zorin

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.


2018 ◽  
Vol 230 ◽  
pp. 03010 ◽  
Author(s):  
Liubov Ksonshkevych ◽  
Olena Krantovska ◽  
Mykola Petrov ◽  
Sergii Synii ◽  
Anna Uhl

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.


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