scholarly journals Влияние добавок модификаторов вязкости на реологическое поведение цементных систем для 3D-печати

2020 ◽  
Vol 44 (3) ◽  
pp. 129-138
Author(s):  
Keyword(s):  
Rheological Behavior ◽  
Effective Viscosity ◽  
Experimental Studies ◽  
Water System ◽  
Aggregate Stability ◽  
Mineralogical Composition ◽  
Plastic Properties ◽  
Cement Pastes ◽  
Viscosity Modifiers ◽  
Form Stability

Представлены результаты экспериментальных исследований реологического поведения модельных цементных систем как матриц смесей для 3D-печати. В проведенных экспериментах использованы: для изучения реологического поведения – сдавливающие тесты; для оценки показателя пластичности, характеризующего способность смесей сохранять агрегативную устойчивость в процессе экструзии, – сдавливающий тест с постоянной скоростью деформирования; для оценки формоустойчивости – сдавливающий тест с постоянной скоростью нагружения, по результатам которых найдены значения структурной и пластической прочности, пластических деформаций цементных систем, характеризующие их способность сохранять форму при действии возрастающих сжимающих напряжений в процессе печати. Получены количественные данные о влиянии видов и дозировок неорганических модификаторов вязкости различного химико-минералогического состава и дисперсности на пластичность и формоустойчивость цементных смесей. Установлено, что для рассмотренных составов наиболее эффективными модификаторами вязкости являются тонкодисперсные метакаолин и каолин со средним размером частиц 5 мкм. Регулирование вязкопластических свойств и агрегативной устойчивости цементных систем определяется изменением свойств дисперсионной среды в гетерогенной системе «цемент–вода». Определены рациональные дозировки данных модификаторов, при которых обеспечиваются критериальные значения показателей пластичности для процессов 3D-печати, структурной прочности и деформативности при действии нагрузки. Ключевые слова: 3D-печать, цементная смесь, модификатор вязкости, реологическое поведение, пластичность, формоустойчивость. The results of experimental studies of the rheological characteristics of cement pastes as a matrix of 3D-printable mixtures are presented. The squeezing tests were used to evaluate the rheological behavior. To evaluate the plasticity, which characterizes the ability of 3D-printable mixtures to maintain aggregate stability during the extrusion process, the squeezing test with a constant deformation rate was used. To evaluate the form stability a squeezing test with a constant loading speed was used. As a result, the structural and plastic strength, plastic deformations of fresh cement pastes were estimated as criteria of their ability to maintain shape under compressive pressure during the printing process. Quantitate data on influence of types and dosages of inorganic viscosity modifiers with various chemical and mineralogical composition and sizeparticles on the plasticity and form stability of cement pastes was obtained. It was found that the most effective viscosity modifiers are fine-dispersed metakaolin and kaolin with an average size-particle of 5 μm. As a result of using the most effective viscosity modifiers, adjustment of viscous-plastic properties and aggregate stability of cement pastes can be made by modifying the properties of the dispersion liquid in the heterogeneous "cement–water" system. Reasonable proportions of these modifiers have been obtained, which ensures plasticity, maximum structural strength and minimum deformability of 3D-printable mixtures under load. Keywords: 3D-printing, cement paste, viscosity modifier, rheological behavior, plasticity, form stability.

Masonry: the brittle or plastic material?

2019 ◽  
pp. 22-28
Keyword(s):  
Plastic Material ◽  
Experimental Studies ◽  
Point Of View ◽  
Plastic Properties ◽  
Plastic Deformations ◽  
Base Materials ◽  
Stress States ◽  
Creep Deformations ◽  
Structural Point

The results of experimental studies of masonry on the action of dynamic and static (short-term and long-term) loads are presented. The possibility of plastic deformations in the masonry is analyzed for different types of force effects. The falsity of the proposed approach to the estimation of the coefficient of plasticity of masonry, taking into account the ratio of elastic and total deformations of the masonry is noted. The study of the works of Soviet scientists revealed that the masonry under the action of seismic loads refers to brittle materials in the complete absence of plastic properties in it in the process of instantaneous application of forces. For the cases of uniaxial and plane stress states of the masonry, data on the coefficient of plasticity obtained from the experiment are presented. On the basis of experimental studies the influence of the strength of the so-called base materials (brick, mortar) on the bearing capacity of the masonry, regardless of the nature of the application of forces and the type of its stress state, is noted. The analysis of works of prof. S. V. Polyakov makes it possible to draw a conclusion that at the long application of the load, characteristic for the masonry are not plastic deformations, but creep deformations. It is shown that the proposals of some authors on the need to reduce the level of adhesion of the mortar to the brick for the masonry erected in earthquake-prone regions in order to improve its plastic properties are erroneous both from the structural point of view and from the point of view of ensuring the seismic resistance of structures. It is noted that the proposal to assess the plasticity of the masonry of ceramic brick walls and large-format ceramic stone with a voidness of more than 20% is incorrect, and does not meet the work of the masonry of hollow material. On the basis of the analysis of a large number of research works it is concluded about the fragile work of masonry.

The rheological behavior of fresh cement pastes

1988 ◽  
Vol 18 (3) ◽  
pp. 327-341 ◽  
Author(s):  
Richard Shaughnessy ◽  
Peter E. Clark
Keyword(s):  
Rheological Behavior ◽  
Cement Pastes

scholarly journals Rheological Behavior of Fresh Cement Pastes

Fluids ◽  
2018 ◽  
Vol 3 (4) ◽  
pp. 106 ◽  
Author(s):  
Francisco-José Rubio-Hernández
Keyword(s):  
Rheological Behavior ◽  
Flow Behavior ◽  
Viscoelastic Behavior ◽  
Alternative Methods ◽  
Chemical Additives ◽  
Research Activity ◽  
Cement Pastes ◽  
Blended Cements ◽  
Flow Models ◽  
Mineral Additions

Rheology of a concrete is mainly controlled by the rheological behavior of its cement paste. This is the main practical reason for the extensive research activity observed during 70 years in this research subfield. In this brief review, some areas of the research on the rheological behavior of fresh cement pastes (mixture method influence, microstructure analysis, mineral additions influence, chemical additives influence, blended cements behavior, viscoelastic behavior, flow models, and flow behavior analysis with alternative methods) are examined.

scholarly journals Investigation of the structure of cement conglomerates

2021 ◽  
Vol 266 ◽  
pp. 03005
Author(s):  
D. N. Shabanov ◽  
E. Trambitsky ◽  
E. Borovkova
Keyword(s):  
Strain State ◽  
Residual Life ◽  
Experimental Studies ◽  
Cement Stone ◽  
Virtual Model ◽  
Structural Studies ◽  
Acoustic Sensors ◽  
Cement Pastes ◽  
The Moment ◽  
Physical And Chemical

This article describes the structural studies of a cement conglomerate, its evolution from the moment of formation to the loss of operational properties. Physical and chemical phenomena and interactions of various elements of cement stone are considered. The study of its rheology includes creating a virtual model and monitoring the formation of the structure of cement pastes by acoustic emission (AE). The results of combined experimental studies to determine the residual life of cement stone samples using AE and tensometry methods are presented. The authors created a complex for monitoring the stress-strain state of artificial conglomerates, which includes both internal and acoustic sensors.

Temporal changes of mobile forms of 90Sr on Pripyat River floodplain in vicinity of Chornobyl NPP: measurements and risk assessments for river water contamination

2021 ◽  
Author(s):  
Gennady Laptev ◽  
Oleg Voitsekhovych ◽  
Valentyn Protsak ◽  
Mark Zheleznyak ◽  
Kenji Nanba ◽  
...  
Keyword(s):  
Coming Out ◽  
Water Contamination ◽  
Soil Layer ◽  
Experimental Studies ◽  
Water System ◽  
Water Soluble ◽  
Computational Grids ◽  
Exclusion Zone ◽  
Drastic Increase ◽  
Fuel Particles

<p>Since the 1986 Chornobyl accident transport of radionuclides by Pripyat River shares more than 90% of the annual total flux of radioactivity coming out the Chornobyl Exclusion Zone (ChEZ).  90Sr was the main contributor to this flux. In course of time destruction of the accidentally dispersed "fuel particles" leads to increase of mobile, e.g. water-soluble, forms of 90Sr  on territories affected by, while fixation of 137Cs in soil is reflected by significant reduction in 137Cs aquatic transport outside the ChEZ.</p><p>Heavily contaminated floodplain of the Pripyat River, located in vicinity of ChNPP upstream of Yaniv Bridge up to Ukrainian - Belorussian border, was considered as a “hotspot” with highest risks to the Pripyat and Dnipro water contamination due to recurrent flooding of these territories. This was evidently elucidated after the 1991 ice jam event when drastic increase of 90Sr in water was observed. The dikes splitting leftbank floodplain from the Pripyat river channel were constructed in 1992-1993. Yet, it is still important to quantify the amount of 90Sr that can be washed off the floodplain due to potential dike breakage caused by the extreme floods. </p><p>Key parameters used to describe status of radionuclide in reaching equilibrium in soil-water system are the distribution coefficient (Kd) and kinetic rate that is reciprocal of typical time scale of desorption processes. These parameters subsequently were estimated in 1991 on the basis of batch experiment carried out with the soil monoliths sampled from the Pripyat floodplain ( Laptev and Voistekhovich, 1991). Results were used in the 2D model COASTOX for justification the construction of protecting dikes (Zheleznyak at al., 1992).</p><p>To analyze current ability of 90Sr to be washed off the floodplain, soils monoliths were collected in 2020. The experimental studies of the soil cores collected from same location as the monoliths allowed to estimate mobile speciation of 90S and calibrate mass-exchange parameters. Amount of the readily exchangeable forms of 90Sr in soils significantly increased from 10-30% in the first years after the accident up to 65-75% as to 2020. Results of field and laboratory  studies were used for simulation the scenarios of 90Sr washing off the floodplain during the dikes breaks on the basis of contemporary version of COASTOX model, that includes the parallel algorithms for numerical solution of the model equations on the unstructured computational grids for multi CPU and GPU systems. Approaches for the modelling of the secondary release of 90Sr due the rapid destruction of “fuel particles” are considered. Taking into account two concurrent processes - decrease of amount of 90Sr in uppermost soil layer due to decay and downward vertical migration (1), amid increased amount of exchangeable forms of 90Sr (2), one could project subsequent increasing of 90Sr  in Pripyat and Dnipro river waters downstream the source in case of the dike breakage scenarios. On the other hand, computer simulation suggests that the maximal values of the 90Sr concentrations expected to be not higher than the measured ones during the high floods events after the accident.</p><p> </p>

Rheological behavior of fresh cement pastes with a graphene oxide additive

2016 ◽  
Vol 31 (6) ◽  
pp. 574-584 ◽  
Author(s):  
Qin Wang ◽  
Jian Wang ◽  
Chun-xiang Lv ◽  
Xi-you Cui ◽  
Shi-yu Li ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Rheological Behavior ◽  
Cement Pastes ◽  
Oxide Additive

Towards Rational Design of Porcelain Tile Glazes

2014 ◽  
Vol 92 ◽  
pp. 138-147 ◽  
Author(s):  
José Luis Amorós
Keyword(s):  
Kinetic Model ◽  
Effective Viscosity ◽  
Rational Design ◽  
Mineralogical Composition ◽  
Chemical Transformations ◽  
Crystalline Phases ◽  
Complex Behaviour ◽  
Different Temperatures ◽  
The One ◽  
Porcelain Tile

The complexity of porcelain tile glaze compositions translates into equally complex behaviour during firing in which, concurrently or in partially overlapping form, very different processes develop, such as the dissolution of crystalline phases, the crystallisation of new phases, and sintering phenomena. This complexity, and the scarcity of studies relating to the subject, make it extremely difficult to formulate such glaze compositions scientifically and efficiently. The present study analysed the physico-chemical transformations that occurred during the firing of these glazes, focusing in particular on the sintering process and its kinetics. A kinetic model was developed, first, which describes the sintering of complex glaze compositions (containing more than five components) with significant frit contents (45–70%) that devitrify crystalline phases during firing. A second, more comprehensive kinetic model was then developed, involving a formal multi-step kinetic model that encompassed even more complex glaze compositions (up to nine components), to calculate the effective viscosity of the glaze melt. This property was compared, on the one hand, with the effective viscosity obtained experimentally by hot stage microscopy (HSM) and, on the other, with that estimated theoretically from the chemical and mineralogical composition of the material, at different temperatures. The results obtained by the two methods exhibited very good agreement. The concept of effective viscosity provides a better understanding of the role played by the different glaze constituents and the firing conditions in sintering, enabling more rational design of these materials.

The Hydration of Magnesium Phosphate Cements: Effect of Powder Characteristics on the Reaction Kinetics

2008 ◽  
Vol 591-593 ◽  
pp. 833-838 ◽  
Author(s):  
M. Arlete Carvalho ◽  
Ana M. Segadães
Keyword(s):  
Room Temperature ◽  
Setting Time ◽  
Ammonium Phosphate ◽  
Mineralogical Composition ◽  
Magnesium Phosphate ◽  
Water Addition ◽  
Cement Pastes ◽  
Powder Characteristics ◽  
Magnesia Powder ◽  
Cold Setting

The setting reaction of magnesium phosphate cements starts with water addition to a mixture of ammonium phosphate and magnesium oxide, is very fast and takes place at room temperature (cold setting). Literature shows that controversy is still going on about the reaction mechanism, hence, about the effect on the setting time of factors such as the water/cement ratio or the magnesia specific surface area. This work is focused on the magnesia powder characteristics, which were varied by calcining MgO at temperatures ranging from 900 to 1050°C, for periods of 30 to 60 min. Cement pastes were obtained by mixing MgO and diammonium phosphate with water and setting aids. The pastes were left to set in air and were characterized in terms of mineralogical composition (XRD) and microstructure (SEM). The results obtained show how the combined effect of the magnesia characteristics can be used to control the workability and adjust the setting time.

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