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Calorimetric comparison of portland cements containing silica fume and metakaolin

Is silica fume, like metakaolin, characterized by pozzolanic activity that is more specific than generic?

Journal of Thermal Analysis and Calorimetry
Authors: R. Talero and V. Rahhal

Abstract  

This new study must be regarded to be a direct outcome of two previous studies published by these same authors, which were conducted to respond to interesting questions brought out about the effect of silica fume, SF and metakaolins, M and MQ, on the heat of hydration of portland cements, PC, with very different C3A and C3S contents. The answer to these so interesting questions has been the primary objective of the present research. For this purpose, the same PC, PC1 (14% C3A) and PC2 (≈0% C3A), metakaolins, silica fume and blended cements were once again used more 60/40 for sulphate attack, and the same analytical techniques (CC, pozzolanicity and XRD analysis) and parameters determined as well. In this new research, the sulphate attack was determined by two accelerated methods: Le Chatelier-Ansttet and ASTM C 452-68. The experimental results of sulphate attack mainly, have demonstrated definitively that the high, rapid and early pozzolanic activity exhibited by SF also is, as in the case of the two metakaolins, more specific than generic, for it indirectly stimulated greater C3A than C3S hydration, but only in the first 16 h monitored in this study. Thereafter it is the contrary, i.e., anti- or contra-specific for the same purpose. And the longer the hydration time, the more anti- or contra-specific it became, since, when exposed to sulphate attack, SF blended cements resisted or even prevented the aggressive attack against PC1 which, with a higher C3A content than PC2, was the more vulnerable of the two. By contrast, metakaolin MQ not only failed to hinder or prevent the attack, but heightened its effects, rendering it more intense, aggressive and rapid, leading to what could be called a rapid gypsum attack.

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1 Introduction Metakaolin (MK) is the anhydrous calcined form from the clay mineral kaolinite. It is a manufactured product rather than a by-product. It is formed when china clay (mineral kaolin) is heated to a temperature between 600 and 800 °C

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Journal of Thermal Analysis and Calorimetry
Authors: Carolina Resmini Melo, Elidio Angioletto, Humberto Gracher Riella, Michael Peterson, Márcio Roberto Rocha, Aline Resmini Melo, Luciano Silva, and Susane Strugale

structure, forming amorphous metakaolin. With paper production increasing and an improvement in product quality sought, the paper industry has generated large amounts of waste that have become an environmental and economical concern. To address this

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different type of pozzolanic materials as additives to mortars and concretes, as well as to compare their properties. Most studies on the kinetics of metakaolin–lime interaction have been carried out under conditions, which are modeling the practical

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Metakaolin as supplementary cementitious material

Optimization of kaolin to metakaolin conversion

Journal of Thermal Analysis and Calorimetry
Authors: E. Badogiannis, G. Kakali, and S. Tsivilis

Summary In this paper the optimization of the kaolin calcination is studied, aiming at using the produced metakaolin as supplementary cementitious material. Representative samples of poor Greek kaolin (Milos island) and a high purity commercial kaolin were tested. Samples were heated at different temperatures during different times. The optimization of calcination conditions was studied by DTA-TG and XRD analysis of the raw and thermal treated kaolin samples, by pozzolanic activity analysis of metakaolins and finally by strength development analysis of cement-metakaolin mixtures. This approach showed that heating at 650°C for 3 h is efficient to convert poor kaolins with low alunite content to highly reactive metakaolins. However in the case of kaolin with a high alunite content, thermal treatment at 850°C for 3 h is required in order to remove undesirable SO3. Evidence was found that poor kaolins can be efficiently used for the production of highly reactive metakaolins.

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) metakaolin (MK-M) for the standard and Si-rich (70.11 wt% of SiO 2 ) metakaolin (MK-T) for sand-rich. MK-M has 39.34 wt% of SiO 2 and 5.11 wt% of TiO 2 while MK-T has 28.21 wt% of Al 2 O 3 and 0.66 wt% of TiO 2 . The others elements were <3 wt% for MK

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Abstract  

In this work two aluminic pozzolans (metakaolins) and a non-pozzolan were added to two Portland cements with very different mineral composition, to determine the effect on the rate of heat release and the mechanisms involved. The main analytical techniques deployed were: conduction calorimetry, pozzolanicity and XRD. The results showed that the two metakaolins induced stimulation of the hydration reactions due to the generation of pozzolanic activity at very early stage, because of their reactive alumina, Al2O3 r− contents, mainly. Such stimulation was found to be more specific than generic for more intense C3A hydration than C3S, at least at very early on into the reaction, and more so when 7.0% SO3 was added, and for this reason, such stimulation is described as ‘indirect’ to differentiate it from the ‘direct’ variety. As a result of both stimulations, the heat of hydration released is easy to assimilate to a Synergistic Calorific Effect.

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Abstract  

In this study the calorimeter was applied to follow the early hydration of mixtures produced using three different synthetic slag vitreous materials, differing with alumina to silica ratio and mixed or not with synthetic two different metakaolin additions (kaolin heated with sodium containing admixture or without admixture). These mixtures were processed with sodium/potassium hydroxide solutions and placed inside the chamber of calorimeter. The kinetics of hydration process was thus characterized and the hydraulic properties of slag–metakaolin mixtures were very well assessed. Substantial heat evolution was found in the presence of activators, in many cases exceeding 100 J g–1 for 24 h process; heat evolved on hydration with water only was very poor, below 20 J g–1 after 24 h. The rate of heat evolution vs. time plots showed specific shape, more or less similar to the typical heat evolution curves reported for cements. Finally, some conclusions were drawn and the amount/concentration of activators was selected for further studies.

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Abstract  

In order to evaluate the pozzolanic activity of metakaolin, several pastes were prepared, by mixing metakaolin with hydrated lime, in different ratios. The pastes were stored in standard conditions (RH=991%, T=251C) and evaluated using thermal analysis (DTA/TG), X-ray diffraction (XRD), compressive strength tests and mercury intrusion porosimetry (MIP), in time. The obtained results revealed that the compounds formed are CSH, C2ASH8 and C4
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$A\overline C H$$ \end{document}
11 while C4AH13 was not detected up to 270 days of curing. The calcium hydroxide consumption increases as the initial amount of the metakaolin in the paste augments. The maximum strength development is obtained for metakaolin/lime ratio:1.
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Abstract  

This paper reports an experimental study on the magnesium sulphate resistance of mortar specimens incorporating 0, 10 and 20% of metakaolin (MK). The evidence of the attack was evaluated through the content of calcium hydroxide (portlandite) and formation of magnesium hydroxide (brucite) by thermal analysis (thermogravimetric and derivative thermogravimetric analysis). The mechanical degradation of the mortar specimens was evaluated through splitting tensile tests after 200 days of exposition to the magnesium solution. The addition of metakaolin resulted in a reduction in the content of calcium hydroxide and in a smaller formation of brucite in comparison with reference mixture. A tensile strength loss of about 7% was observed for the metakaolin mortars submitted to the magnesium solution attack for 200 days.

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