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. 6 Durehovi , A. , ‘ Hydration of alite and C 3 A and changes of some structural characteristics of cement pastes by addition of silica fume ’, Proceedings of 8 th International Congress on Chemistry of Cement, Vol. III

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ash and silica fume. HPC has become a widely used material that is widely used in engineering applications. A superplasticizer is also required in the mix to achieve the required properties. In addition, various types of additives are typically added

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Abstract  

The hydration of two calcium hydroxide— silica fume mixtures was studied at 25°C, these are Mix I and Mix II with molar lime/silica ratios of 1 and 1.7, respectively. The free lime, free silica and chemically combined water contents were determined at various time of hydration from which the molar CaO/SiO2 ratios of the formed calcium silicate hydrate, C−S−H, were calculated. The results indicated that hydration takes place in six steps where C−S−H (I) is formed at early stages of hydration, for Mix I, While for Mix II formation of C−S−H (I) and C−S−H (II) were detected by X-ray diffraction analysis and differential thermal analysis.

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. This necessitated the utilization of micro filler silica fume (SF) as a supplementary cementitious material that fills up the voids in the concrete thereby enhancing its performance [ 2 ]. Various researches on the utilization of SF have shown improved

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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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% retaining at this sieve size according to ASTM C618 [ 5 ] as compared to the average particle size of PC at & 10–15 &m. Silica fume occurred as a by-product of the ferro-silicon alloys and silicon metal industries, on the other hand, is very fine at

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Abstract  

The most widely identified degradation process suffered by calcium aluminate cement (CAC) is the so-called conversion of hexagonal calcium aluminate hydrate to cubic form. This conversion is usually followed by an increase in porosity determined by the different densities of these hydrates and the subsequent loss of strength. Mixes of calcium aluminate cement (CAC) and silica fume (SF) or fly ash (FA) represent an interesting alternative for the stabilization of CAC hydrates, which might be attributed to a microstructure based mainly on aluminosilicates. This paper deals with the microstructure of cement pastes fabricated with mixtures CAC-SF and CAC-FA and its evolution over time. Thermal analysis (DTA/TG), X-ray diffraction (XRD) and mid-infrared spectroscopy (FTIR) have been used to assess the microstructure of these formulations.

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Artificial pozzolanic cement pastes containing burnt clay with and without silica fume

Physicochemical, microstructural and thermal characteristics

Journal of Thermal Analysis and Calorimetry
Authors: M. S. Amin, S. A. Abo-El-Enein, A. Abdel Rahman, and Khaled A. Alfalous

, lowering heat of hydration, and thermal expansion [ 1 ]. Recently, the use of pozzolanic cement is increasing world-wide because it needs less energy for production. Early hydration reactions of Portland cement–silica fume blends were studied and

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Journal of Thermal Analysis and Calorimetry
Authors: S. A. Abo-El-Enein, Z. M. Abou-Gamra, F. I. El-Hosiny, and S. M. A. El-Gamal

The hydration of two calcium hydroxide-silica fume mixtures was studied at 25°C. The mixtures were prepared at lime/silica molar ratios of 1.0 and 1.7. The free lime, free silica and chemically combined water contents were determined after various periods of hydration (0.5 h-90 days). Thus, the molar ratios CaO/SiO2 and H2O/SiO2 molar in the calcium silicate hydrates (C-S-H) formed could be derived. The hydrates formed were identified by using differential thermal analysis. The mechanism of the hydration-gardening thermal analysis. The mechanism of the hydration-hardening reaction between lime and silica fumes was suggested. The changes in the molar ratios CaO/SiO2 and H2O/SiO2 in the C-S-H formed with the time of hydration were found to follow the same trends as observed during the hydration course for the suggested mechanism.

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