An Impact of Carbon Nanostructured Additives on the Kinetics of Cement Hydration

2015 ◽  
Vol 725-726 ◽  
pp. 425-430 ◽  
Author(s):  
Artem Frolov ◽  
Artemiy Cherkashin ◽  
Luka Akimov ◽  
Nikolai Vatin ◽  
Tatiana Koltsova ◽  
...  

There are supplements that could accelerate or slow down the process of setting and formation of the cement stone structure. After examining the effect of these particles, we can predict how they could influence on the growth of concrete strength. It is possible to assess the effect of supplementation activity using the thermo-kinetic method by exothermic effect, which is obtained by wetting and hydration of cement. A calorimetric research of the effect of cement-carbon material was held in this article.

2020 ◽  
Vol 8 (4) ◽  
pp. 37-42
Author(s):  
Andrei Pavlov ◽  
Yurii Gol'tsov ◽  
Levon Mailyan ◽  
Sergey Stel'makh ◽  
Evgeniy Shcherban' ◽  
...  

The analysis of the influence of ultraviolet irradiation of building sand, which is a filler in a concrete mixture, on the dependence of the strength of concrete on the content of filler is carried out. With an increase in the content of sand due to the hydrophilicity of the surface of its particles in the mixture, the amount of free water required for the hydration of cement and the formation of cement stone decreases. Along with a decrease in the content of binder cement, this factor is an additional reason for a decrease in the strength of concrete with an increase in the content of sand. Ultraviolet irradiation leads to dehydration of the surface of the sand particles and the appearance of hydrophobic centers. As the hydrophobicity of the sand in the concrete mix increases, the content of free water available for cement hydration increases, and the strength of the cement stone increases. The change in the hydrophobicity of the surface of sand particles depending on the time of irradiation is non-monotonic. Therefore, there is an optimal UV activation mode that provides the greatest increase in concrete strength.


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.


2021 ◽  
Vol 316 ◽  
pp. 1019-1024
Author(s):  
O. A. Ignatova ◽  
A. A. Dyatchina

The paper presents the studies’ results of chemical composition, structure, and physico-mechanical properties of high-calcium ashes from the Kansk-Achinsk coals (2017-2019 selection). It was found that ash has a complex poly-mineral composition and contains hydraulically active minerals and oxides of СаОfr, β-C2S, CA, C3A, C4AF, C2F, CaSO4. According to the content of CaOfr, MgO does not meet standards’ requirements. The uniformity of the volume change is maintained by the composition with 50% of cement. The structure and hardening kinetics of ash and ash-cement stone compositions, obtained from the test of normal density, were analyzed. It was established that the hardening of compositions with ash from the Kansk-Achinsk coals was largely influenced by ash minerals. An equivalent amount of cement in composite binders cannot be replaced. In order to obtain a positive effect, compositions with ash instead cement of no more than 30% and a part of fine aggregate, without exceeding the ratio of ash: cement = 1: 1, should be used.


2013 ◽  
Vol 539 ◽  
pp. 25-29
Author(s):  
Wei Chen ◽  
Pei Liang Shen ◽  
Jian Xin Lu ◽  
Wan Ru Zhang

The variations of dielectric constant and the amplitude of reflected EM wave of concrete during the first 3 days are measured with Ground Penetrating Radar (GPR) at 20 oC. The amplitude decreases sharply after mixing with water, and then increases till a stabilized stage, followed by a gradual decline. The relative dielectric constant decreases with increasing hydrating time. The results show that the dielectric properties of concrete can be used as an effective way of studying the kinetics of concrete setting and hardening process at early ages.


1976 ◽  
Vol 54 (20) ◽  
pp. 3192-3199 ◽  
Author(s):  
Tahir R. Khan ◽  
Cooper H. Langford

In this report, determination of unbound aquo iron species is accomplished by a kinetic method involving reaction with sulfosalicylic acid (SSA) on a time scale which is very short with respect to reaction of SSA with the glutathione complexes of iron. The data are used to calculate conditional binding constants for Fe(III) to glutathione. Binding constants in 0.1 M ionic strength media were obtained between pH 1 and 2.4 by the kinetic method, and near pH = 3 by spectrophotometry and by examination of the ratio of rate of complex formation and dissociation. The conditional binding 'constant' between pH 1 and 3 is represented as pK = −1.96 – 0.50pH. This is consistent with the importance of reactions involving only very limited proton release. Spectrophotometric data show that the —OH group on Fe(OH)2+ is lost on glutathione complexing. Kinetics of the complex formation reaction between aquo iron(III) species and glutathione are slower than rates of reaction of iron(III) with simple ligands.The glutathione system is regarded as a model system important to natural water chemistry because it is a widely distributed biological sulfur-containing chelating agent.


Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2112 ◽  
Author(s):  
Marco Pepe ◽  
Carmine Lima ◽  
Enzo Martinelli

The early-age performances of cement-based mixtures are governed by cement hydration reactions. As a matter of fact, the heat generated during the setting and hardening phases due to the hydration processes increases the temperatures within the concrete elements while it starts developing its mechanical properties. These thermal stresses can cause the premature cracking of the cementitious matrix and undermine the long-term durability of the whole concrete element, especially in the case of massive structures where the dissipation of generated heat is more difficult. It is worth highlighting that the kinetics of cement hydration is mainly governed by the mixture composition; on the other hand, the heat generated during the setting and hardening is also influenced by the geometry of the element and/or its curing conditions. In this context, this study presents a numerical procedure intended to simulate the hydration reactions, and hence scrutinize the development of concrete properties at the early-age. Specifically, considering the variation of several factors, such as concrete strength class, element size and curing conditions, a comprehensive parametric analysis is presented herein, leading to the proposal of a simplified approach for both predicting the time evolution of the concrete mechanical performances at the early-age and mitigating the risk of premature cracking.


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.


Polymers ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 357 ◽  
Author(s):  
Marita Pigłowska ◽  
Beata Kurc ◽  
Łukasz Rymaniak ◽  
Piotr Lijewski ◽  
Paweł Fuć

The main aim of this study is to estimate the kinetic and thermodynamic parameters of thermal decomposition of starches by the Coats–Redfern method. This procedure is a commonly used thermogravimetric analysis/difference thermal gravimetry/differental thermal analysis (TG/DTG-DTA) kinetic method for single rate form. The study also shows a proposed method for reactive hydroxyl groups content on the starch surface determination, and values were in range of 960.21–1078.76 mg OH per 1 g of starch. Thermal processing revealed the thermophysical properties of biomass for the kinetics of decomposition estimation. Activation energies reached the values in range of approximately 66.5–167 kJ·mol−1. This research also enables the determination of the temperature conditions required for becoming the desired form of material. Therefore, it is necessary to achieve the requested compact porous structure in an activation process, because in the native state, the polymer exhibits limited applications as a result of thermal decomposition, low shear stress, retrogradation, and syneresis, hence the low solubility in organic solvents. Thermodynamic parameters and reactive hydroxyl groups in this article review are innovative and have not yet been found in the literature.


2014 ◽  
Vol 670-671 ◽  
pp. 339-343 ◽  
Author(s):  
Aleksey Adamtsevich ◽  
Andrey Pustovgar ◽  
Stanislav Pashkevich ◽  
Aleksey Eremin ◽  
Andrey Zhuravlev

Nowadays, there is a great demand for the accelerated hardening construction mixtures. That causes the necessity to the methods development for testing the effectiveness of accelerators, well as the analysis of kinetics of cement systems hydration in the early stages of hardening. This paper presents the results of an experimental research of interrelation between the growth kinetics of cement-based binder system strength and the heat release for pure cement hydration. How it was found, two compositions of construction mix, which are identical in mineral composition and differ in the presence of mono-functional accelerator, a comparison of strength growth dynamics can be carried out indirectly via the integral curve of heat release, obtained using the method of isothermal calorimetry.


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