scholarly journals Alkali Ion Concentration Estimations in Cement Paste Pore Solutions

2019 ◽  
Vol 9 (5) ◽  
pp. 992 ◽  
Author(s):  
Miguel Sanjuán ◽  
Esteban Estévez ◽  
Cristina Argiz
Keyword(s):  
Composite Materials ◽  
Cement Paste ◽  
Amorphous Silica ◽  
Reliable Method ◽  
Pore Solution ◽  
Ion Concentration ◽  
Alkali Silica Reaction ◽  
Distribution Method ◽  
Structural Problems ◽  
Over Time

The alkalinity of the pore solution is of great interest for evaluating the rising of the alkali–silica reaction (ASR) when reactive amorphous silica is found in some aggregates in some cement-based composites. This reaction is not desirable because it generates swelling gel materials around the aggregates, which produce an expansive pressure inside concrete over time, and can cause the cracking of concrete, leading to serious structural problems. The purpose of this study is to develop a quick, easy and reliable method to estimate the available alkali concentrations in the pore solution of cement-based composites. The bound alkalis were initially calculated based on Taylor’s alkali distribution method. The proposed procedure to estimate the available alkalis content is a reliable method for use in construction and building composite materials.

Effect of Pore Structure and Ion Concentration of Solution on the Formation of Ettringite in Composite Cement Paste

2020 ◽  
Vol 993 ◽  
pp. 1382-1387
Author(s):  
Yan Zheng ◽  
Su Ping Cui
Keyword(s):  
Pore Structure ◽  
Cement Paste ◽  
Pore Solution ◽  
Formation Rate ◽  
Ion Concentration ◽  
Hydration Reaction ◽  
Composite Cement ◽  
Ettringite Formation ◽  
Effective Expansion ◽  
Cement System

Under the background of shrinkage cracking of cement and concrete, ettringite is regarded as the most effective expansion source because of its outstanding expansion characteristics. In order to study the expansion mechanism of ettringite, the growth process and formation conditions of ettringite in composite cement system were studied by means of SEM, MIP and ICP. The effects of pore structure and ion concentration of pore solution on the morphology and expansion properties of ettringite were also analysed in this paper. The results show that the pore structure of cement paste directly affects the expansion properties of ettringite. It is verified that there is no obvious linear relationship between the expansion rate of ettringite and its quantity. The concentration of SO42- and Al(OH)4- in pore solution is the determinant of ettringite formation rate and quantity in composite cement system at the initial stage of hydration reaction. The change of crystallinity of ettringite will be directly caused by pH.

Test Methods for Rheological Properties of Self-Compacting Concrete Pastes

2011 ◽  
Vol 338 ◽  
pp. 396-400
Author(s):  
Bao Guo Ma ◽  
Hui Xian Wang ◽  
Jian Huang ◽  
Liu Qing Song
Keyword(s):  
Rheological Properties ◽  
Cement Paste ◽  
Test Methods ◽  
General Study ◽  
Self Compacting Concrete ◽  
Cement Pastes ◽  
Different Types ◽  
Over Time

This paper provides a general study on cement paste flow which derived from self- compacting concretes. Rheometer, Marsh cone and mini-slump cone were used to evaluate fluidity of cement pastes containing superplasticizers of different types and dosages and loss of fluidity over time. There is a superplasticizer saturation dosage beyond which no significant fluidity increase can be found. This paper evaluated the effect of these three methods using rheometer as control and the optimum superplasticizer type for the preparation of self-compacting concrete was suggested.

THE INFLUENCE OF THE COMPOSITION AND SIZE OF THE FRACTIONS OF THE COMPOSITE GRAVEL FILLER WITH AN EPOXY MATRIX ON ITS WEAR

2021 ◽  
Vol 3 (144) ◽  
pp. 100-107
Author(s):  
Aleksandr M. Mikhal’chenkov ◽  
◽  
Anna A. Tyureva ◽  
Ivan A. Borshchevskiy ◽  
Larisa S. Kiseleva
Keyword(s):  
Wear Resistance ◽  
Composite Materials ◽  
Epoxy Matrix ◽  
Protective Coatings ◽  
Research Purpose ◽  
Effective Diameter ◽  
Wear Process ◽  
The Matrix ◽  
Sand And Gravel ◽  
Over Time

The widespread use of polymer-based composite materials made it possible to replace expensive metal alloys, increase the strength indicators of structures and improve tribotechnical properties. Their use as protective coatings for structural elements operating in an abrasive environment has yielded good results in increasing wear resistance, which is especially important for parts of tillage tools. (Research purpose) The research purpose is in studying the influence of the composition and size of the fractions of the composite gravel filler with an epoxy matrix on its wear. (Materials and мethods) The article considers five composite materials with different compositions. The prototypes were hollow cylinders with dimensions that provide the contact area necessary for the passage of all processes of abrasive wear. The abrasive composition consisted of a mixture of sand and gravel with a fraction size of about 30-40 millimeters. (Results and discussion) The changes in the wear over time are directly proportional and this confirms the classical views on the wear process. The experiments was conducted on the installation of authors’ design. (Conclusions) The wear over time for experimental composites is the same and is expressed in a straight- line relationship; the maximum wear resistance is a composite in which gravel particles have a size of 2.25 millimeters with its content in the matrix of about 60 mass parts. At the same time, gravel with an effective diameter of 2.25 millimeters creates optimal conditions for self-organization of the wear process and provides a relatively low value of the friction coefficient.

scholarly journals Alkali-Silica Reaction Resistance and Pore Solution Composition of Low-Calcium Fly Ash-Based Geopolymer Concrete

2020 ◽  
Vol 5 (11) ◽  
pp. 96
Author(s):  
Jiawei Lei ◽  
Jiajun Fu ◽  
En-Hua Yang
Keyword(s):  
Fly Ash ◽  
Pore Solution ◽  
Systematic Investigation ◽  
Alkali Silica Reaction ◽  
Geopolymer Concrete ◽  
Portland Cement Concrete ◽  
Solution Composition ◽  
Low Calcium ◽  
Underlying Mechanisms ◽  
One Year

Low-calcium fly ash-based geopolymer concrete is generally reported to be less vulnerable to alkali-silica reaction (ASR) than conventional ordinary Portland cement concrete. However, the lack of understanding of pore solution composition of the low-calcium fly ash-based geopolymer limits the investigation of the underlying mechanisms for the low ASR-induced expansion in the geopolymer concrete. This study presents a systematic investigation of the pore solution composition of a low-calcium fly ash-based geopolymer over a period of one year. The results show that the pore solution of the fly ash geopolymer is mainly composed of alkali ions, silicates, and aluminosilicates species. The lower expansion of the geopolymer concrete in the current study is most probably due to the insufficient alkalinity in the geopolymer pore solution as the hydroxide ions are largely consumed for the fly ash dissolution.

Prediction and Analysis of Reinforcement Corrosion in Simulated Concrete Pore Solution Based on Neural Network

2020 ◽  
Vol 34 (14) ◽  
pp. 2059047
Author(s):  
Fengjiao Jiang ◽  
Jinxin Gong ◽  
Jichao Zhu ◽  
Huan Wang ◽  
Weibo Song
Keyword(s):  
Neural Network ◽  
Equivalent Circuit ◽  
Pore Solution ◽  
Equivalent Circuit Model ◽  
Chloride Ion ◽  
Ion Concentration ◽  
Equivalent Circuits ◽  
Chromium Alloy ◽  
Ph Values ◽  
Impedance Characteristics

The corrosion of reinforcement has always been a problem to be solved in the field of architecture. In this paper, the corrosion characteristics of chromium alloy steel under different pH conditions are studied. The impedance characteristics and equivalent circuit are predicted by neural network model. First of all, in simulated pore solution with different pH values, the characteristics of Nyquist impedance spectroscopy of the whole chromium alloy under passivation stage and the damaged passivation film of reinforcing bars under initial corrosion stage have been found. Then, according to the difference of impedance characteristics under different pH values, different equivalent circuits have been established and [Formula: see text] values of different equivalent circuits under different chloride ion concentration have been calculated. By fitting the electrochemical parameters of the equivalent circuit with [Formula: see text] values, the equivalent circuit model which can be predicted by neural network has good consistency with the equivalent circuit which can be predicted by [Formula: see text] values.

Formation of Complex Non-Equilibrium Morphologies of Calcite via Biomimetic Processing

2003 ◽  
Vol 774 ◽  
Author(s):  
Yi-yeoun Kim ◽  
Laurie B. Gower
Keyword(s):  
Thin Films ◽  
Local Solution ◽  
Ion Concentration ◽  
Mineralization Process ◽  
Liquid Precursor ◽  
Inorganic Composites ◽  
Biomimetic Approach ◽  
Biomimetic Processing ◽  
Over Time ◽  
Non Equilibrium

AbstractOur biomimetic approach for fabricating organic-inorganic composites with structures similar to biominerals is based on a novel mineralization process, called the Polymer-Induced-Liquid-Precursor (PILP) process. This process enables the deposition of non-equilibrium mineral morphologies of calcite under low-temperature and aqueous-based conditions [1], including patterned thin films of calcite. We have recently found that when a surplus of acidic polymer is added, the patterned mineral films act as a secondary template for directing new crystal outgrowths, which form into complex morphologies of calcite with time, such as fibrous mats and “horsetails”. Two interdependent factors, the polymer and Ca-ion concentration, which change the local solution environment over time, appear to modulate the creation of these different structures. Such observations may provide clues for unraveling the long-standing mystery of how biological systems fabricate their sophisticated and complex morphologies.

scholarly journals Effect of lithium nitrate on the reaction between opal aggregate and sodium and potassium hydroxides in concrete over a long period of time

2017 ◽  
Vol 65 (6) ◽  
pp. 773-778 ◽  
Author(s):  
J. Zapała-Sławeta ◽  
Z. Owsiak
Keyword(s):  
Electron Microscopy ◽  
Pore Solution ◽  
Alkali Silica Reaction ◽  
Lithium Nitrate ◽  
X Ray ◽  
Long Period ◽  
Chemical Admixtures ◽  
Mortar Bar ◽  
Sodium And Potassium ◽  
Scanning Electron

AbstractAlkali-silica reaction (ASR) is a reaction between amorphous or poorly crystallized siliceous phase, present in aggregates, and sodium and potassium hydroxides in the pore solution of concrete. Chemical admixtures such as lithium compounds are known to have high potential of inhibiting ASR. The aim of this study was to determine the effect of lithium nitrate on ASR in mortars containing high reactive opal aggregate over a long period of time. Mortar bar expansion tests were performed and microstructures of mortar bars were observed by scanning electron microscopy coupled with an energy dispersive X-ray microanalyser. Results from this study showed that effectiveness of lithium nitrate in mitigating ASR was limited over a long period of time. A larger amount of ASR gel which was formed in the presence of lithium nitrate indicated that the deterioration processes intensify within longer periods of time, which so far has not been observed in literature. Microscopic observation confirmed the presence of alkali-silica gel and delayed ettringite in mortars with lithium nitrate.

Simple Approach for Computing Chloride Diffusivity of (Non)Carbonated Concrete

2008 ◽  
Vol 385-387 ◽  
pp. 281-284 ◽  
Author(s):  
In Seok Yoon
Keyword(s):  
Experimental Data ◽  
Structural Properties ◽  
Cement Paste ◽  
Scientific Knowledge ◽  
Pore Solution ◽  
Simple Approach ◽  
Hardened Cement ◽  
Hardened Cement Paste ◽  
Chloride Diffusivity ◽  
Concrete Materials

The purpose of this study is to establish a simple approach to compute the chloride diffusivity of (non)carbonated concrete. The chloride diffusivity of concrete should is defined, based on engineering and scientific knowledge of cement and concrete materials. In this paper, parameters affecting the chloride diffusivity, such as the diffusivity in pore solution, tortuosity, micro-structural properties of hardened cement paste, volumetric portion of aggregate, are taken into consideration in the calculation of the chloride diffusivity of noncarbonated concrete. For carbonated concrete, reduced porosity due to carbonation is calculated and used for calculating the chloride diffusivity. The results are compared with experimental data and previous research works.

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