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The Mechanism of the Formation and Transformation of ettringite

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Journal of Wuhan University of Technology(Materials Science) 2006年第3期21卷 158-161页

作者：彭家惠 Department of Building Materials Chongqing University Chongqing 400045 China

The formation and transformation of ettringite were studied by measuring the ion concentration in liquid phase and analyzing the composition in solid phase. The effects of C3A, gypsum lime and C-S-H gel on ettringite formation and transformation were also investigated. The experimental results shuw, that, when gypsum was presented in solid phase, the composition of liquid phase was in favor of ettringite formation. ettringite formation consisted of three reactions including the formation of [ Al （OH）6 ]^3- octahedral, formation of Ca-Al polyhedra prism in which Ca and Al polyhedra arranged alternately, as well as entrance of SO4^2- into the channel of polyhedra. [ Al （OH）6 ]^3- formation, which was the slowest reaction, controlled ettringite formation. The concentration of AlO2^- was a main factor that influenced ettringite formation. After gypsum in solid phase was consumed, [ SO4^2- ] decreased quickly and [ AlO2^- ] increased, and it was possible that ettringite transformed into hydrated monsulfate calcium aluminate （ be called M in short） in thermodymanics. The rate of transformation was controlled by diffusion of AlO2^- .

关键词： ettringite hydrated monsulfate calcium aluminate stability transform control step

Effect of Stearic Acid on ettringite Formation

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Journal of Materials Science & Technology 2002年第3期18卷 263-265页

作者： Essam A.KisharDepartment of Chemistry, Faculty of Girls, Ain Shams University, Cairo, Egypt [ Manuscript received March 29, 2001, in revised form June 11, 2001] Ain Shams Univ Fac Girls Dept Chem Cairo Egypt

The hydration reaction of a mixture of tricalcium aluminate (C3A) and gypsum with the molar ratio of 1:3 was carried out at room temperature and a water/solid ratio of 4.0. The hydration was carried out in presence of 0, 1 and 3% stearic acid and the mixes were designated as A, B and C, respectively. ettringite was the only hydration product formed in the presence and absence of stearic acid. Phase composition, microstructure, infra-red analysis as well as degree of hydration were carried out for the different hydration mixtures. The rate of ettringite formation in the presence of 3% stearic acid was accelerated during the first half hour of hydration, and then retardation was occurred. In the presence of 1% stearic acid the ettringite formation was accelerated first till 3 days, then retardation was observed at later hydration ages.

关键词： Stearic acid Hydration ettringite

EXPERIMENTAL EVALUATION ON MODULUS OF EQUIVALENT HOMOGENEOUS ettringite

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Acta Mechanica Solida Sinica 2009年第4期22卷 320-327页

作者： Minghua Zhang Jiankang Chen Jue Zhu Jiangying Chen Department of Mechanics and Engineering Science Ningbo University Ningbo 315211 China

In the present study, the average modulus of delayed ettringite is evaluated by an experimental method combined with theoretical analysis. Firstly, the delayed ettringite crystal is synthesized by chemical reaction of Aluminum sulfate and calcium hydroxide. Secondly, specimens are obtained by compressing the delayed ettringite crystal under different pre-loads. Thirdly, the variation of the modulus of the specimen with different pre-loads is tested using Instron material test machine and the SHPB technique, respectively. It is found that the experimental data may be suitably fitted by Boltzmann Function. Finally, the porosity of the specimen is detected using the saturation method, and the effect of the porosity on the modulus is analyzed by the Eshelby＇s equivalent inclusion method and the Mori-Tanaka＇s scheme. The static and dynamic modulli of the equivalent homogeneous ettringite obtained in present study are approximately 10.64 GPa and 24.61 GPa, respectively.

关键词： ettringite equivalent homogeneous materials Boltzmann Function modulus

Calcium Carbonate and ettringite Induced Efflorescence in CAC-Anhydrite Binary Systems

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Journal of Wuhan University of Technology(Materials Science) 2024年第5期39卷 1129-1137页

作者： SUN Zixuan CHEN Yuting XU Linglin LIU Siyu YU Long PAN Feng WANG Chaoqiang WU Kai YANG Zhenghong Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education School of Materials Science and EngineeringTongji UniversityShanghai 201804China Shanghai Construction No.5(Group)Co. Ltd.Shanghai 200063China School of Material Science and Engineering Chongqing Jiaotong UniversityChongqing 400074China

We focused on the efflorescence induced microstructural evolution of ettringite-rich systems prepared with calcium aluminate cement(CAC)and *** effects of anhydrite on the visible efflorescence,and the corresponding capillary absorption of CAC-anhydrite mortars were *** composition and microstructure of efflorescence-causing substances were investigated by optical microscope,in-situ Raman spectroscopy,scanning electron microscope,energy dispersive spectrometer,thermogravimetric analysis,and differential scanning calorimetry,at *** indicate that,besides the calcium carbonate,ettringite is another main component of efflorescence-causing *** with the neat CAC mortars,the addition of anhydrite has a significant effect on the degree of efflorescence by acting on the composition of hydration products and pore *** addition,methods are proposed for the prevention of efflorescence of CAC-anhydrite binary system.

关键词： calcium aluminate cement anhydrite efflorescence ettringite phase assemblage pore structure

Isothermal Adsorption Characteristics and Kinetics of Cr Ions onto ettringite

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Journal of Wuhan University of Technology(Materials Science) 2019年第3期34卷 587-595页

作者： WANG Xin CUI Suping School of Materials Science and Engineering Beijing University of TechnologyBeijing100124China China Building Materials Academy State Key Laboratory of Green Building MaterialsBeijing100024China

The isothermal absorption properties and kinetic model of Cr(VI) and Cr(III) onto ettringite were investigated using the batch adsorption method. IR analysis was used to study the difference and mechanism of the adsorption of chromium ions with different valence states. The results show that the adsorption of Cr(III) onto ettringite at 20 ℃ agrees with Langmuir’s isothermal model. The ion binding stability was significantly greater than that of Cr(VI). While the adsorption of Cr(VI) onto ettringite agrees with Freundlich’s isothermal model, the D-R model fits the adsorption isotherms of two types of valence Cr(R2>0.994). It can be concluded that the adsorption of Cr(III) onto ettringite is mainly by chemical adsorption and that the adsorption of Cr(VI) onto ettringite is mainly by physical adsorption. Dynamic model fitting and model parameter analyses show that the adsorption of Cr(III) onto ettringite agrees with the pseudo second order kinetics model given by Lagergren. The formation of chemical bonds is the main factor causing the fast adsorption. Cr(VI) adsorption is mainly dominated by liquid film diffusion, and the adsorption rate is much slower than that of Cr(III) adsorption.

关键词： ettringite Cr adsorption kinetics mechanism

Crystal Growth of[Ca3Al(OH)6·12H2O]2·(SO4)3·2H2O (ettringite) Studied Under Microgravity Conditions

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Journal of Wuhan University of Technology(Materials Science) 2020年第5期35卷 893-899页

作者： Meier M R LEI L Rinkenburger A Plank J Technische Universitat Miinchen Chair for Construction Chemistry85747 GarchingLichtenbergstrafie 4Germany

On parabolic flights,the growth of ettringite,[Ca3Al(OH)6·12H2O]2·(SO4)3·2H2O,a major reaction product of cement with water which forms instantaneously,was crystallized under microgravity conditions and *** the experiments,Ca(OH)2/Al2(SO4)3 solutions were combined and reacted for 10?s,followed by immediate filtration of the suspension and subsequent quenching with *** the ettringite crystals,the size,aspect ratios,quantity and morphology were determined and the results were compared with those from identical experiments performed under terrestric *** microgravity,generally smaller crystals (l-2.9 μm) precipitated in larger amount than under normal gravity (l-3.5 μm).The aspect ratios of the crystals grown under terrestric or microgravity condition were comparable at about *** is assumed that the reason for the smaller ettringite crystals is the absence of convection leading to more initial nuclei,but slower crystal growth which is diffusion ***,no preference relative to the ion transport to the different faces of the crystals *** results contribute to the understanding of the mineralization of inorganic salts under microgravity conditions for which hitherto only a handful of examples were reported.

关键词： crystallization ettringite microgravity morphology nucleation

Properties of ettringite Type Expansive Agent

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Journal of Wuhan University of Technology(Materials Science) 2001年第4期16卷 53-56页

作者：李悦 Beijing Polytech Univ Coll Architecture & Civil Engn Beijing 100022 Peoples R China Wuhan Univ Technol Wuhan 430070 Peoples R China

By employing different forms and amounts of materials, many kinds of ettringite type expansive agents had been prepared. The relationship between the compositions and properties of expansive agents was analyzed. The design methods of expansive agent have been put forward according to the property, requirement of expansive concrete.

关键词： ettringite expansive agent composition property

Assessment of deterioration in RHA-concrete due to magnesium sulphate attack

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International Journal of Minerals,Metallurgy and Materials 2010年第6期17卷 691-696页

作者： G.A. Habeeb H.B. Mahmud N.B.A.A. Hamid Department of Civil Engineering Faculty of Engineering University of Malaya

The assessment of magnesium sulphate attack on concretes containing rice husk ash （RHA, 20wt% of the cementitious materials） with various average particle sizes was investigated. The total cementitious materials were 390 kg and the water-to-binder ratio （W/B） was 0.53 for all mixtures. Specimens were initially cured in water for 7 d and then immersed in the 3wt% magnesium sulphate solution for up to 111 d of exposure. The specimens were subjected to drying-wetting cycles to accelerate sulphate attack. In addition to the visual monitoring of the specimens, the concrete specimens were subsequently tested for compressive strength, dynamic modulus of elasticity, and length and mass changes. The results show that the specimens exposed to sulphate attack exhibit higher strength and dynamic modulus than those kept in water. The length change is negligible and can be attributed to the normal swelling of concrete. On the other hand, concretes suffers mass loss and surface spalling and softening; the fine RHA-concrete results in a better resistance. For the accelerated sulphate attack method used in this study, mass change and visual monitoring are recommended for assessing the deterioration degree and the effectiveness of supplementary cementitious materials to resist sulphate attack.

关键词： concretes pozzolan ettringite rice husk ash (RHA) magnesium sulphate

Influence of Nano-SiO2 Addition on Properties of Sulphoaluminate Cement Based Material

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Journal of Wuhan University of Technology(Materials Science) 2017年第1期32卷 106-112页

作者：马保国李海南 MEI Junpeng LI Xiangguo State Key Laboratory of Silicate Materials for Architectures Wuhan University of TechnologyWuhan 430070 China

The influences of different nano-SiO2（NS） contents on the mechanical properties and rheological behavior of sulfoaluminate cement（SAC） based composite materials were *** show that with increasing content of NS,the apparent viscosity,and shearing strength of fresh paste gradually increase but the fluidity *** a dosage of 3.0%NS,the tensile and flexural strengths of mortars at 56 days were increased by 87.0%and 84.6%,respectively,compared with that in the absence of NS,indicating that the toughness of hardened mortars is significantly ***,the exothermic peaks of hydration are obviously increased and will earlier occur,and the second and the third peaks appear 2.61 hours and 2.56 hours earlier,respectively than that in the absence of NS,and the hydration of SAC before 8 hours is *** forming mechanism of strengths was revealed by scanning electron microscopy（SEM）,hydration heat,X-ray diffraction（XRD） and derivative thermogravimetry（DTG）.The micro-aggregate filling effect and nucleation effect at early age and weak pozzolanic effect at late age of NS make the microstructure more compact,which obviously enhances the strength of SAC mortars.

关键词： sulfoaluminate cement nano-SiO2 ettringite strengths hydration process