Нанофибробетон: многоуровневое армирование

Concrete is the most commonly used building material worldwide. One of its main disadvantages is the fragility of fracture and low crack resistance. The use of dispersed reinforcement of concrete composites is a promising direction in solving this type of problem. Dispersed fibers, evenly distributed over the entire volume of the material, create a spatial frame and contribute to the inhibition of developing cracks under the action of destructive forces. In order to increase the fracture toughness of concrete, dispersed fiber reinforcement is increasingly used in practice. The beginning of crack nucleation occurs at the nanoscale in the cement matrix. Thus, the use of nano-reinforcement with dispersed nanofibers can have a positive effect on the crack resistance of the cement composite. It is proposed to consider carbon nanotubes as such nanofibers. The presence of carbon nanofibers changes the microstructure and nanostructure of cement modified with carbon nanotubes. The result of the processes occurring in capillaries and cracks are deformations in the intergranular matrix, the free flow of which is prevented by rigid clinker grains and nanocarbon tubes, which creates a certain stress intensity at the tips of the separation cracks. The working hypothesis is confirmed that the required fracture toughness of structural concrete is provided by multi-level reinforcement: at the level of the crystalline aggregate of cement stone – carbon nanotubes, and at the level of fine-grained concrete – various macro-sized fibers (steel, polymer). Reinforcement of a crystalline joint with carbon nanotubes leads to an increase in the fracture toughness of the matrix (cement stone) by 20 %, compressive strength by 12 %, and tensile strength in bending by 20 %. When reinforcing at the level of fine-grained concrete, we obtain a composite – nanofibre-reinforced concrete with fracture toughness.Бетон является наиболее распространенным строительным материалом во всем мире. Основными его недостатками являются хрупкость при растяжении и низкая трещиностойкость. Применение дисперсного армирования бетонных композитов – перспективное направление в решении такого рода задач. Дисперсные волокна, равномерно распределенные по всему объему материала, создают пространственный каркас и способствуют торможению развития трещин под действием разрушающих сил. Для повышения трещиностойкости бетона на практике все чаще применяют армирование дисперсными волокнами. Начало зарождения трещины происходит на наноуровне в цементной матрице. Таким образом, применение наноармирования дисперсными нановолокнами может положительно сказаться на трещиностойкости цементного композита. В качестве таких нановолокон предлагается рассматривать углеродные нанотрубки. Присутствие углеродных нановолокон изменяет микроструктуру и наноструктуру цемента, модифицированного углеродными нанотрубками. Результатом процессов, происходящих в капиллярах и трещинах, являются деформации в межзерновой матрице, свободному течению которых препятствуют жесткие зерна клинкера и наноуглеродные трубки, что создает в вершинах разделительных трещин некоторую интенсивность напряжения. Подтверждена рабочая гипотеза, что требуемая трещиностойкость конструкционного бетона обеспечивается многоуровневым армированием: на уровне кристаллического заполнителя цементного камня – углеродными нанотрубками, на уровне мелкозернистого бетона – различными видами макроразмерной фибры (стальные, полимерные). Армирование углеродными нанотрубками кристаллического сростка приводит к повышению показателя вязкости разрушения матрицы (цементного камня) на 20 %, прочности на сжатие на 12 %, прочности на растяжение при изгибе на 20 %. При армировании на уровне мелкозернистого бетона получаем композит – нанофибробетон с вязкостью разрушения

Nanofiber Concrete: Multi-Level Reinforcement

Concrete is the most commonly used building material worldwide. One of its main disadvantages is the fragility of fracture and low crack resistance. The use of dispersed reinforcement of concrete composites is a promising direction in solving this type of problem. Dispersed fibers, evenly distributed over the entire volume of the material, create a spatial frame and contribute to the inhibition of developing cracks under the action of destructive forces. In order to increase the fracture toughness of concrete, dispersed fiber reinforcement is increasingly used in practice. The beginning of crack nucleation occurs at the nanoscale in the cement matrix. Thus, the use of nano-reinforcement with dispersed nanofibers can have a positive effect on the crack resistance of the cement composite. It is proposed to consider carbon nanotubes as such nanofibers. The presence of carbon nanofibers changes the microstructure and nanostructure of cement modified with carbon nanotubes. The result of the processes occurring in capillaries and cracks are deformations in the intergranular matrix, the free flow of which is prevented by rigid clinker grains and nanocarbon tubes, which creates a certain stress intensity at the tips of the separation cracks. The working hypothesis is confirmed that the required fracture toughness of structural concrete is provided by multilevel reinforcement: at the level of the crystalline aggregate of cement stone – carbon nanotubes, and at the level of fine-grained concrete – various macro-sized fibers (steel, polymer). Reinforcement of a crystalline joint with carbon nanotubes leads to an increase in the fracture toughness of the matrix (cement stone) by 20 %, compressive strength by 12 %, and tensile strength in bending by 20 %. When reinforcing at the level of fine-grained concrete, we obtain a composite – nanofibre-reinforced concrete with fracture toughness

Strength Indicators of Fiber Reinforced Concrete with Carbon Nanomaterials

Concrete composites with low defects, dense and homogeneous, with a high degree of adhesion between the cement matrix and aggregates, as well as a high ratio between static tensile and compressive strengths and plasticity have the best crack resistance characteristics. This ratio increases in the case of the use of fiber-reinforced concrete. Modern research in nanotechnology focuses on the management of matter at the nanoscale level, which makes it possible to create materials with new properties. Due to the high aspect ratio, flexibility, high strength and rigidity, carbon nanotubes (CNTs) exhibit reinforcing properties. Due to their nanoscale features, CNTs interact with a complex network of calcium-silicate-hydrate binder (C – S – H), contribute to a decrease in porosity and compaction of the cement stone structure, increase the shear forces of matrix adhesion in the contact zone. Thus, there are all prerequisites to assert that fiber concrete with a cement matrix modified with carbon nanotubes will have the required high strength characteristics and crack resistance due to multilevel dispersed reinforcement and the efficient operation of fiber in a nanomodified concrete matrix. This article presents the results of testing samples made of cement stone, concrete and fiber concrete with carbon nanotubes. The presence of carbon nanotubes in cement stone contributes to an increase in compressive strength by 11 %, tensile strength during bending by 20 %. The test results of samples made of reinforced fiber concrete modified with nanocarbon materials have shown an increase in tensile strength during bending up to 109 %, tensile strength during splitting up to 82 %, axial tensile strength up to 78 %

Brussowvirus SW13 Requires a Cell Surface-Associated Polysaccharide To Recognize Its Streptococcus thermophilus Host

Four bacteriophage-insensitive mutants (BIMs) of the dairy starter bacterium Streptococcus thermophilus UCCSt50 were isolated following challenge with Brussowvirus SW13. The BIMs displayed an altered sedimentation phenotype. Whole-genome sequencing and comparative genomic analysis of the BIMs uncovered mutations within a family 2 glycosyltransferase-encoding gene (orf06955(UCCSt50)) located within the variable region of the cell wall-associated rhamnose-glucose polymer (Rgp) biosynthesis locus (designated the rgp gene cluster here). Complementation of a representative BIM, S. thermophilus B1, with native orf06955(UCCSt50) restored phage sensitivity comparable to that of the parent strain. Detailed bioinformatic analysis of the gene product of orf06955(UCCSt50) identified it as a functional homolog of the Lactococcus lactis polysaccharide pellicle (PSP) initiator WpsA. Biochemical analysis of cell wall fractions of strains UCCSt50 and B1 determined that mutations within orf06955(UCCSt50) result in the loss of the side chain decoration from the Rgp backbone structure. Furthermore, it was demonstrated that the intact Rgp structure incorporating the side chain structure is essential for phage binding through fluorescence labeling studies. Overall, this study confirms that the rgp gene cluster of S. thermophilus encodes the biosynthetic machinery for a cell surface-associated polysaccharide that is essential for binding and subsequent infection by Brussowviruses, thus enhancing our understanding of S. thermophilus phage-host dynamics.IMPORTANCE Streptococcus thermophilus is an important starter culture bacterium in global dairy fermentation processes, where it is used for the production of various cheeses and yogurt. Bacteriophage predation of the species can result in substandard product quality and, in rare cases, complete fermentation collapse. To mitigate these risks, it is necessary to understand the phage-host interaction process, which commences with the recognition of, and adsorption to, specific host-encoded cell surface receptors by bacteriophage(s). As new groups of S. thermophilus phages are being discovered, the importance of underpinning the genomic elements that specify the surface receptor(s) is apparent. Our research identifies a single gene that is critical for the biosynthesis of a saccharidic moiety required for phage adsorption to its S. thermophilus host. The acquired knowledge provides novel insights into phage-host interactions for this economically important starter species

Многопараметрическая методика оценки показателей качества наномодифицированного фибробетона для строительной площадки

Nanomodified fiber-reinforced concrete is a building material for which the required characteristics of fracture toughness are a distinctive feature. Determination of the stress intensity factor of fiber-reinforced concrete makes it possible to correctly assess the resistance of the material during the formation and development of cracks. The proposed multi-parameter methodology for assessing the quality indicators of nanomodified fiber-reinforced concrete makes it possible to evaluate the quality of a fiber-reinforced concrete structure in construction and laboratory conditions. To carry out control at the construction site, modern and long-used methods of non-destructive testing are used: ultrasonic sounding, ultrasonic tomography, elastic rebound, separation with chipping. For laboratory studies, the technique provides for the manufacture of prism samples that can be molded or cut from the body of the structure. This methodology makes it possible to obtain in laboratory conditions such material parameters as tensile strength in bending, tensile strength in splitting, critical stress intensity factor for normal separation, critical stress intensity factor for transverse shear, energy consumption for individual stages of deformation and destruction of the sample, as well as to evaluate the uniformity of distribution fibers. Moreover, it is provided to obtain all the parameters on one sample from the series, which eliminates errors and inaccuracies in the quality indicators of the material associated with different conditions of hardening, molding, inaccuracies in duplicating the composition.Наномодифицированный фибробетон – это строительный материал, отличительной особенностью которого являются требуемые характеристики трещиностойкости. Определение коэффициента интенсивности напряжений фибробетона дает возможность правильно оценить сопротивление материала при образовании и развитии трещин. Предлагаемая многопараметрическая методика оценки показателей качества наномодифицированного фибробетона позволяет оценить качество фибробетонной конструкции в строительных и лабораторных условиях. Для осуществления контроля на строительной площадке используют современные и давно применяемые методы неразрушающего контроля: ультразвуковое зондирование, ультразвуковую томографию, упругий отскок, отрыв со скалыванием. Для лабораторных исследований методика предусматривает изготовление призматических образцов, которые могут быть отлиты в форму или вырезаны из тела конструкции. Эта методика позволяет получить в лабораторных условиях такие параметры материала, как прочность на изгиб, прочность при растяжении на раскалывание, коэффициент интенсивности напряжений при нормальном отрыве, коэффициент интенсивности напряжений при поперечном сдвиге, энергозатраты на отдельные стадии деформации и разрушения образца, а также оценить равномерность распределения волокон. Более того, предусмотрено получение всех параметров на одном образце из серии, что исключает ошибки и неточности в показателях качества материала, связанные с различными условиями твердения, формования, погрешностями при дублировании состава

Multi-Parameter Methodology for Assessing Quality Indicators of Nanomodified Fiber-Reinforced Concrete for Construction Site

Nanomodified fiber-reinforced concrete is a building material for which the required characteristics of fracture toughness are a distinctive feature. Determination of the stress intensity factor of fiber-reinforced concrete makes it possible to correctly assess the resistance of the material during the formation and development of cracks. The proposed multi-parameter methodology for assessing the quality indicators of nanomodified fiber-reinforced concrete makes it possible to evaluate the quality of a fiber-reinforced concrete structure in construction and laboratory conditions. To carry out control at the construction site, modern and long-used methods of non-destructive testing are used: ultrasonic sounding, ultrasonic tomography, elastic rebound, separation with chipping. For laboratory studies, the technique provides for the manufacture of prism samples that can be molded or cut from the body of the structure. This methodology makes it possible to obtain in laboratory conditions such material parameters as tensile strength in bending, tensile strength in splitting, critical stress intensity factor for normal separation, critical stress intensity factor for transverse shear, energy consumption for individual stages of deformation and destruction of the sample, as well as to evaluate the uniformity of distribution fibers. Moreover, it is provided to obtain all the parameters on one sample from the series, which eliminates errors and inaccuracies in the quality indicators of the material associated with different conditions of hardening, molding, inaccuracies in duplicating the composition

Оптимизация состава нанофибробетона по вязкости разрушения модификацией матрицы

Concrete is a quasi-brittle building material that has low tensile strength. The process of its destruction under loading is inhomogeneous, due to the nature of the concrete structure mass, consisting of components with different physical and mechanical properties. Gradual deformation and destruction can be characterized as a process of formation and development of microcracks. The presence of different-sized components in concrete makes it possible to consider its structure as a multi-level system. In this system, each level is a matrix with its own structural inclusions, which play both a structure-forming role and the role of stress concentrators under the action of mechanical loads. The critical stress intensity factor is a good indicator of the crack resistance (fracture toughness) of a material. Nanoconcrete, from the point of view of a multilevel system, is a concrete composite with crack propagation inhibitors at the level of the cementing substance (carbon nanotubes are consi-dered as inhibitors). The presence of fiber fibers at subsequent scale levels allows us to consider concrete as a composite with multi-level dispersed reinforcement (nanofiber concrete). The paper discusses the change of concrete fracture toughness indicator (crack resistance) with dispersed reinforcement of the matrix at different structural levels. The presented for normal separation of notched cubes under eccentric compression with the determination of the stress intensity factor for concrete modified with carbon nanotubes acting as crack propagation inhibitors at the level of cementing substance (nanoconcrete), as well as for nanofiber concrete with dispersed reinforcement at the level of fine-grained concrete. Based on experimental studies by non-equilibrium methods of fracture mechanics, compositions of nanofiber-reinforced concrete of maximum crack resistance (fracture toughness) with different fiber concentrations and several types of matrices modified with nanocarbon additives are proposed in the paper.Бетон – квазихрупкий строительный материал, который имеет низкую прочность при растяжении. Процесс его разрушения при нагружении носит неоднородный характер, обусловленный сущностью структуры бетонной массы, состоящей из компонентов с различными физико-механическими свойствами. Постепенное деформирование и разрушение можно охарактеризовать как процесс образования и развития микротрещин. Наличие в бетоне разных по размеру компонентов позволяет рассматривать его строение как многоуровневую систему. В этой системе каждый уровень представляет собой матрицу со своими структурными включениями, которые играют как структурообразующую роль, так и роль концентраторов напряжений при действии механических нагрузок. Критический коэффициент интенсивности напряжений является хорошим показателем трещиностойкости (вязкости разрушения) материала. Нанобетон, с точки зрения многоуровневой системы, представляет собой бетонный композит с ингибиторами распространения трещин на уровне цементирующего вещества (в качестве ингибиторов рассматриваются углеродные нанотрубки). Присутствие фибровых волокон на последующих масштабных уровнях позволяет рассматривать бетон как композит с многоуровневым дисперсным армированием (нанофибробетон). В статье рассмотрено изменение показателя вязкости разрушения (трещиностойкости) бетона при дисперсном армировании матрицы на разных структурных уровнях. Приведены результаты испытаний на нормальный отрыв образцов-кубов с надрезами при внецентренном сжатии с определением коэффициента интенсивности напряжений для бетона, модифицированного углеродными нанотрубками, выступающими в качестве ингибиторов распространения трещин на уровне цементирующего вещества (нанобетон), а также для нанофибробетонов с дисперсным армированием на уровне мелкозернистого бетона. На основании экспериментальных исследований неравновесными методами механики разрушения предложены композиции нанофибробетона максимальной трещиностойкости (вязкости разрушения) с различной концентрацией фибры и несколькими типами матриц, модифицированных наноуглеродными добавками

Материалы на основе цемента, модифицированные наноразмерными добавками

The most common and reliable material without which modern construction is indispensable is concrete. The development of construction production is pushing for new solutions to improve the quality of concrete mix and concrete. The most demanded and significant indicators of a concrete mixture are the compressive strength and mobility of the concrete mixture. Every year, the volume of research on nanomaterials as modifying components of concrete is significantly increasing, and the results indicate the prospects for their use. Nanoparticles with a large specific surface are distinguished by chemical activity, can accelerate hydration and increase strength characteristics due to nucleation and subsequent formation of C–S–H and compaction of the material microstructure. Sol of nanosilica, which can be used instead of microsilica from industrial enterprises, and carbon nanomaterial have a wide reproduction base. This paper presents studies of these types of nanomaterials and the results of their application in cement concrete. Studies have shown that the effect is also observed with the introduction of an additive containing only one type of nanoparticles. The dependence of the obtained characteristics of cement concretes on the content of these nanomaterials has been established. It has been found that the best results were obtained with an additive in which the above-mentioned nanomaterials were used together. Compressive strength of  heavy concrete samples, improved by the complex nanodispersed system, was 78.7 MPa, which exceeds the strength of the sample containing the CNT additive in a pair with a super-plasticizer by 37 %.  The paper proposes the mechanism for  action of the presented complex additive.Самым распространенным и надежным материалом, без которого не обходится современное строительство, является бетон. Развитие строительного производства подталкивает к новым решениям в улучшении качества бетонной смеси и бетона. Наиболее востребованные и значимые показатели бетонной смеси – прочность при сжатии и подвижность бетонной смеси. С каждым годом исследований наноматериалов в качестве модифицирующих компонентов бетона становится больше, а результаты указывают на перспективность их применения. Наночастицы, обладающие большой удельной поверхностью, отличаются химической активностью, могут ускорять гидратацию и повышать прочностные показатели за счет зародышеобразования и последующего формирования C–S–H, уплотнения микроструктуры материала. Широкую базу воспроизводства имеют золь нанокремнезема, который может быть использован взамен микрокремнезема с индустриальных предприятий, и углеродный наноматериал. В статье представлены исследования данных видов наноматериалов и результаты их применения в цементных бетонах. Исследования показали, что эффект наблюдается также при введении добавки, содержащей только один вид наночастиц. Установлена зависимость получаемых характеристик цементных бетонов от количества данных наноматериалов. Выявлено, что наилучшие результаты были получены с добавкой, в которой совместно использовались вышеперечисленные наноматериалы. Прочность на сжатие образцов тяжелого бетона, улучшенная комплексной нанодисперсной системой, составила 78,7 МПа, что превышает прочность образца, содержащего добавку углеродных нанотрубок в паре с суперпластификатором, на 37 %. Изучен механизм действия представленной комплексной добавки

Oxygen transport in Pr nickelates: Elucidation of atomic-scale features

Pr2NiO4+δ oxide with a layered Ruddlesden–Popper structure is a promising material for SOFC cathodes and oxygen separation membranes due to a high oxygen mobility provided by the cooperative mechanism of oxygen migration involving both interstitial oxygen species and apical oxygen of the NiO6 octahedra. Doping by Ca improves thermodynamic stability and increases electronic conductivity of Pr2 − xCaxNiO4+δ, but decreases oxygen mobility due to decreasing the oxygen excess and appearing of 1–2 additional slow diffusion channels at x ≥ 0.4, probably, due to hampering of cooperative mechanism of migration. However, atomic-scale features of these materials determining oxygen migration require further studies. In this work characteristics of oxygen diffusion in Pr2 − xCaxNiO4+δ (x = 0–0.6) are compared with results of the surface analysis by X-ray photoelectron spectroscopy and modeling of the interstitial oxygen migration by the plane-wave density functional theory calculations. According to the X-ray photoelectron spectroscopy data, the surface is enriched by Pr for undoped sample and by Ca for doped ones. The O1s peak at ~531 eV corresponding to a weakly bound form of surface oxygen located at Pr cations disappears at ~500 °C. Migration of interstitial oxygen was modeled for a I4/mmm phase of Pr2NiO4+δ. The interstitial oxygen anion repulses the apical one in the NiO6 octahedra pushing it into the tetrahedral site between Pr cations. The calculated activation barrier of this migration is equal to 0.585 eV, which reasonably agrees with the experimental value of 0.83 eV obtained by the oxygen isotope exchange method. At the same time, for the model compound Ca2NiO4+δ, obtained by isomorphic substitution of Pr by Ca in Pr2NiO4+δ, calculations implied formation of the peroxide ion comprised of interstitial and lattice oxygen species not revealed in the case of incomplete substitution (up to PrCaNiO4+δ composition). Hence, calculations in the framework of the plane-wave density functional theory provide a realistic estimation of specificity of oxygen migration features in Pr2NiO4+δ doped by alkaline-earth metals. © 2019 Elsevier B.V.Russian Science Foundation, RSF: 16-13-00112Support by Russian Science Foundation (Project 16-13-00112 ) is gratefully acknowledged