scholarly journals Ultrafast transfer strength of reinforced concrete sleepers by Using complex additives

2021 ◽  
pp. 44-63
Author(s):  
Andrii Plugin ◽  
Olena Kaliuzhna ◽  
Olga Borziak ◽  
Oleksii Plugin ◽  
Oleksandr Savchenko
Keyword(s):  
Energy Intensity ◽  
Cement Hydration ◽  
Experimental Investigations ◽  
Cement Stone ◽  
Hydration Products ◽  
Heat Regime ◽  
Electron Microscopic ◽  
Initial Stage ◽  
Early Strength ◽  
Mineral Additives

The influence of superplasticizers-polycarboxylates and their complex additives withaccelerants - electrolytes and dispersion of calcium hydroxylates on the early strength of concretefor concrete of concrete sleepers has been studied. It was found that the use of superplasticizerspolycarboxylates can improve the early strength of the concrete after heat treatment, but eachadditive must be checked for consistency with the cement used. Approx Complex additives withaccelerators in conditions of natural hardening ensure an increase in the early strength of concrete,but some of them, which accelerate natural hardening, can reduce the strength after WWTP and mustbe checked before use. Electron-microscopic examinations of the structure of cement stone withadditives were carried out and it was found that the additive of only policarboxylate does not changethe structure of hydration products. Complex additives lead to formation of additional number ofcrystalline hydrates of AFm- and/or AFt-phases. The scheme of development of the cement hardeningprocess and the initial stage of cement hardening without or with additives has been developed. Bymeans of which the highest accelerating effect of the complex addition of polycarboxylate andcalcium hydroxylate dispersions was established by experimental investigations, Dispersion particlesincrease surface area where crystallization (condensation) of cement hydration products takes placeand ensures faster filling of spaces between cement particles (mineral additives) with them, fillers)with establishment of lances with electro-heterogeneous contacts. As a result of potentiodynamic andmicroscopic investigations it was established that the tested additives in the dosages do not causecorrosion effect on the steel reinforcement bars. Transmission strength values of 32 MPa for sleepersafter 24 years of hardening under low-heat regime and after 2 days of natural hardening have beenachieved. The formula for economic efficiency of using additives to reduce the energy intensity ofproduction of concrete sleepers has been proposed.

Influence of Nanoscale Barium Hydrosilicates on Composition of Cement Stone

2016 ◽  
Vol 683 ◽  
pp. 90-94 ◽  
Author(s):  
Anna Nikolaevna Grishina ◽  
Evgeniy Valerjevich Korolev
Keyword(s):  
Composite Materials ◽  
Chemical Composition ◽  
Portland Cement ◽  
Cement Hydration ◽  
Experimental Investigations ◽  
Cement Stone ◽  
Hydration Products ◽  
Efficient Control ◽  
Calcium Hydrosilicates ◽  
Portland Cement Hydration

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.

scholarly journals Effect of C-S-H Nucleating Agent on Cement Hydration

2021 ◽  
Vol 11 (14) ◽  
pp. 6638
Author(s):  
Wenhao Zhao ◽  
Xuping Ji ◽  
Yaqing Jiang ◽  
Tinghong Pan
Keyword(s):  
Fractal Dimension ◽  
Cement Hydration ◽  
Nucleating Agent ◽  
Crystal Nucleation ◽  
Enhancement Effect ◽  
Hydration Products ◽  
Hydration Degree ◽  
Hydration Kinetics ◽  
Cement Mortars ◽  
Early Strength

This work aims to study the effect of a nucleating agent on cement hydration. Firstly, the C-S-H crystal nucleation early strength agent (CNA) is prepared. Then, the effects of CNA on cement hydration mechanism, early strength enhancement effect, C-S-H content, 28-days hydration degree and 28-days fractal dimension of hydration products are studied by hydration kinetics calculation, resistivity test, BET specific surface area test and quantitative analysis of backscattered electron (BSE) images, respectively. The results show that CNA significantly improves the hydration degree of cement mixture, which is better than triethanolamine (TEA). CNA shortens the beginning time of the induction period by 49.3 min and the end time of the cement hydration acceleration period by 105.1 min than the blank sample. CNA increases the fractal dimension of hydration products, while TEA decreases the fractal dimension. CNA significantly improves the early strength of cement mortars; the 1-day and 3-days strength of cement mortars with CNA are more than the 3-days and 7-days strength of the blank sample. These results will provide a reference for the practical application of the C-S-H nucleating agent.

Preparation and Mechanism Analysis of High-Efficiency early Strength Agent

2012 ◽  
Vol 535-537 ◽  
pp. 2483-2487 ◽  
Author(s):  
Ming Sheng Zhang
Keyword(s):  
Cement Hydration ◽  
High Efficiency ◽  
Calcium Nitrate ◽  
Xrd Analysis ◽  
Mechanism Analysis ◽  
Hydration Products ◽  
Mineral Formation ◽  
Early Strength ◽  
Further Development

High-efficiency early strength agents were obtained which included triethanolamine, glycol and calcium nitrate. Then it was tested for concrete. Though text, we find that the compressive strength and flexural strength of the specimen, use of the high-efficiency early strength agent is greatly improved than with its much better not to use high-efficiency early strength agent. With time go on, high-efficiency early strength agent added does not make the strength of concrete worse, but better. Using SEM and XRD analysis technology text high-efficiency early strength agent by adding performances of concrete, including the degree of cement hydration, the morphology of hydration products and the composition of mineral formation. Analysis of the role of high-efficiency early strength agents from the perspective of the mechanism. Identified high-efficiency early strength agent impact on the cement hydration, for the further development of early strength agent to provide a theoretical basis.

Improvement of Wood-Cement Composition Properties with Microsilica Additive

2020 ◽  
Vol 992 ◽  
pp. 162-167
Author(s):  
E.Yu. Gornostaeva ◽  
N.P. Lukuttsova ◽  
D.I. Dryazgov
Keyword(s):  
Thermal Conductivity ◽  
Compressive Strength ◽  
Silicon Dioxide ◽  
Cement Hydration ◽  
Cement Stone ◽  
Hydration Products ◽  
Maximum Increase ◽  
Calcium Hydrosilicates ◽  
Calcium Silicates ◽  
Composition Properties

The properties and microstructure of wood-cement compositions (WCC) with microsilica (MS) additive for the manufacture of small-pieces wall products are studied. The extreme dependences of mean density, thermal conductivity and compressive strength on the content of microsilica additive are established. The mechanism of microsilica effect on wood-cement compositions is offered. Two interrelated factors (chemical and physical) could be distinguished at that. The first factor includes mainly the interaction of silicon dioxide with lime having released during hydration of calcium silicates, i.e. pozzolatic process. The second factor lies in the compaction of wood-cement compositions and the cement stone structure by means of cement hydration products and silica particles. It is established that introducing 20% of microsilica in the composition results in the maximum increase in ultimate compression strength (3 times). It can be explained not only by forming calcium hydrosilicates, uniformly and densely covering the wood aggregate, but by compacting effect of spherical microsilica inclusions, filling the space between the new cement stone formations and wood aggregate.

The Structural Formation of Cement Stone Modified by a Solution of Superabsorbent Polymer

2022 ◽  
Vol 906 ◽  
pp. 59-67
Author(s):  
Alexandr Sergeevich Inozemtcev ◽  
Evgenij Korolev ◽  
Duong Thanh Qui
Keyword(s):  
Portland Cement ◽  
Structure Formation ◽  
Water Loss ◽  
Cement Hydration ◽  
Cement Stone ◽  
Layer By Layer ◽  
Superabsorbent Polymer ◽  
Hydration Products ◽  
Structural Formation ◽  
Strength And Durability

With the development of 3D technologies in construction, the development of formulations that are indifferent to the influence of the environment is in demand. Conditions of intense water loss from cement systems arise during the layer-by-layer printing process. This leads to a decrease in density, high shrinkage, and a decrease in the strength and durability of the composite. The use of superabsorbent polymer (SAP) solutions, in contrast to granules, will provide hardening Portland cement with a water supply for internal care of hydration processes. The aim of the work is to study the effect of SAP solution on the processes of structure formation of cement stone, hardening in unfavorable conditions. In this paper, the features of the structure formation of cement systems in the presence of SAP are established. It is shown that the use of polymer in an amount of no more than 1.5% by the weight of Portland cement provides the formation of a more perfect crystalline structure of the cement stone, which allows for an increase in the degree of cement hydration. When the amount of SAP is ≥ 1.5% by the weight of Portland cement, a decrease in the intensity of the maxima corresponding to hydration products is observed.

scholarly journals Enhancing carbonation and chloride resistance of autoclaved concrete by incorporating nano-CaCO3

2020 ◽  
Vol 9 (1) ◽  
pp. 998-1008
Author(s):  
Guo Li ◽  
Zheng Zhuang ◽  
Yajun Lv ◽  
Kejin Wang ◽  
David Hui
Keyword(s):  
Cement Hydration ◽  
Mercury Intrusion Porosimetry ◽  
Hardened Concrete ◽  
Optimal Dosage ◽  
Hydration Products ◽  
X Ray Diffraction ◽  
Carbonation Depth ◽  
X Ray ◽  
Chloride Resistance

AbstractThree nano-CaCO3 (NC) replacement levels of 1, 2, and 3% (by weight of cement) were utilized in autoclaved concrete. The accelerated carbonation depth and Coulomb electric fluxes of the hardened concrete were tested periodically at the ages of 28, 90, 180, and 300 days. In addition, X-ray diffraction, thermogravimetry, and mercury intrusion porosimetry were also performed to study changes in the hydration products of cement and microscopic pore structure of concrete under autoclave curing. Results indicated that a suitable level of NC replacement exerts filling and accelerating effects, promotes the generation of cement hydration products, reduces porosity, and refines the micropores of autoclaved concrete. These effects substantially enhanced the carbonation and chloride resistance of the autoclaved concrete and endowed the material with resistances approaching or exceeding that of standard cured concrete. Among the three NC replacement ratios, the 3% NC replacement was the optimal dosage for improving the long-term carbonation and chloride resistance of concrete.

Effect of Heavy Metals and Leaching Toxicity of Magnesium Potassium Phosphate Cement

2011 ◽  
Vol 117-119 ◽  
pp. 1080-1083 ◽  
Author(s):  
Bao Guo Ma ◽  
Jing Ran Wang ◽  
Xiang Guo Li
Keyword(s):  
Heavy Metals ◽  
Cement Hydration ◽  
Potassium Phosphate ◽  
National Standard ◽  
Magnesium Phosphate ◽  
Toxicity Tests ◽  
Hydration Products ◽  
Obvious Effect ◽  
Leaching Toxicity ◽  
Magnesium Potassium Phosphate Cement

Solidification / stabilization (S/S) is a popular method for treating solid wastes containing heavy metals. In recent years, it shows positive results of magnesium potassium phosphate cement as stabilizing agent. In the work, the influence of heavy metal Cu、Zn and Pb on magnesium phosphate cement and the leaching behavior of magnesium phosphate cement were studied. Two proportions of cements were employed with hard burned magnesia and potassium phosphate. The hydration products were analyzed by XRD showing that: Cu、Zn and Pb would not take on obvious effect during magnesium phosphate cement hydration process. Leaching toxicity tests showed that: Cu、Zn and Pb were immobilized within cement hydration products through physical fixation, adsorption mechanisms, and the results were far lower than that of the National Standard in China.

scholarly journals Alkali activated cements mix design for concretes application in high corrosive conditions

2018 ◽  
Vol 230 ◽  
pp. 03007 ◽  
Author(s):  
Oleksandr Kovalchuk ◽  
Valentina Grabovchak ◽  
Yaroslav Govdun
Keyword(s):  
Corrosion Resistance ◽  
Phase Composition ◽  
Mix Design ◽  
Cement Stone ◽  
Hydration Products ◽  
Alkali Content ◽  
High Corrosion Resistance ◽  
Corrosion Resistant ◽  
High Corrosion ◽  
Alkali Activated

This paper covers the results of development of corrosion resistant ash alkali-activated cements based on regulation of phase composition of the hydration products through changing the alkali content, content of calciumcontaining cement constituents resulting in the increase strength and density of the cement stone. The results of study suggested to conclude that the cement compositions with predominance in the hydration products of weakly soluble low basic hydrosilicates of calcium, hydrogarnets and minerals similar to natural hydroaluminates exhibited the highest corrosion resistance. The results of comparison suggested to draw a conclusion that the alkali-activated cements Types APC III-400 and ACC V-400, according to National Ukrainian Standard DSTU B V.2.7, had high corrosion resistance compared to that of OPC, thus allowing to recommend the developed cements for the concretes intended for use in aggressive environments, inclusive of sodium and magnesium sulphates and others. Coefficients of corrosion resistance of concretes are higher than 1 after even 42 months.

scholarly journals Monitoring of Early and Late Age Hydration Products of Volcanic Ash Blended Cement Paste

Proceedings ◽  
2019 ◽  
Vol 34 (1) ◽  
pp. 9
Author(s):  
Joseph ◽  
Al-Bahar ◽  
Chakkamalayath ◽  
Al-Arbeed ◽  
Rasheed
Keyword(s):  
Portland Cement ◽  
Cement Paste ◽  
Volcanic Ash ◽  
Cement Hydration ◽  
Blended Cement ◽  
Sustainable Construction ◽  
Hydration Products ◽  
N2 Adsorption ◽  
Complete Replacement ◽  
Blended Cement Paste

One of the major concerns of concrete industries is to develop materials that consume less natural virgin resources and energy to make sustainable construction practices. Efforts have been made and even implemented to use the waste/by product materials such as fly ash, slag, silica fume, and natural pozzolana as a partial or complete replacement for Portland cement in concrete mixtures. The deterioration of concrete structures in the existing hot and cold climates of Gulf Cooperation Council countries, along with chloride and sulphate attack, demands the use of pozzolanic materials for concrete construction. Volcanic ash incorporated cement based concretes are known for its better performance in terms of strength and durability in harsh marine environments. Understanding the cement hydration process and characterizing the hydration products in microstructural level is a complex and interdependent process that allows one to design complex mix proportions to produce sustainable concrete materials. In this paper, the early and late age hydration behavior along with micro- and pore structure of cement paste samples prepared with locally available ordinary Portland cement (OPC) and volcanic ash (VA) obtained from Saudi Arabia was monitored using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric (TGA) and N2-Adsorption analysis. The hydration progress of cement paste samples with different combinations of OPC and VA (0%, 15%, 25%, and 35%) at a w/c ratio of 0.45 after 14, 28, and 90 days were discussed. The qualitative XRD and SEM of cement paste samples showed no new phases were formed during the course of hydration. The disappearance of portlandite with increase in VA content was due to both pozzolanic effect and dilution effect. This was further confirmed quantitatively by the TGA observations that the samples with VA contain less Ca(OH)2 compared to the control specimens. N2 adsorption experiments after 90 days of curing showed larger hysteresis as the VA content increases. The studies show that the incorporation of volcanic ash certainly contributes to the generation of C-S-H and hence the cement hydration progress, especially in the later ages through pozzolanic reactions. A 15–25 % volcanic ash blended cement paste samples showed compact and denser morphological features, which will be highly detrimental for the durability performances.

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