Haut Moyen Âge

Résumé

[[fichier:Europe_and_the_Near_East_at_476_AD.png|vignette|L'Europe, l'Afrique du Nord et le Proche-Orient en 476 illustrent un pendant lequel cet espace bascule de l'Antiquité au Moyen Âge. C'est une période de chevauchement, de transition entre l'Antiquité tardive et le haut Moyen Âge]] Le haut Moyen Âge est une période de l'histoire comprise entre l'Antiquité et le Moyen Âge central, et dont les limites, autrefois claires mais contestées, chevauchent actuellement ces deux périodes, notamment l'Antiquité tardive. Elle possède en outre une délimitation géographique. En effet elle n'est employée, dans sa « période haute », qu'en référence aux territoires ayant appartenu au monde romain, soit les régions d'Europe occidentale, orientale et méridionale, d'Asie et d'Afrique autour du bassin méditerranéen. Cependant, au fur et à mesure qu'on se rapproche du Moyen Âge central, cette limite s'étend progressivement bien au-delà. Ainsi, le haut Moyen Âge est devenu depuis la fin du une not

Source officielle

https://fr.wikipedia.org/wiki/Haut_Moyen_%C3%82ge

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Pozzolanic activity of mechanochemically and thermally activated kaolins in cement

Karen Scrivener, Ruben Anton Snellings

This paper reports on the mechanochemical activation by intensive grinding as an alternative way to produce pozzolanically reactive metakaolin. The physicochemical properties, pozzolanic reactivity and impact on cement hydration of mechanochemically and thermally activated kaolinitic clays were compared. Mechanochemical activation of kaolin led to an amorphous hydrous material with increased specific surface area and high water content. Unlike in thermally activated kaolins, the Al coordination environment was partially retained during mechanochemical treatment. At low clinker replacement levels of 10%, the use of mechanochemically activated kaolins accelerated the hydration of the blended cement. The pozzolanic reaction reduced portlandite contents strongly and from early on. The combined effect of enhanced cement hydration and pozzolanic reaction at early ages was reflected in a higher early age strength development (up to 7 days). The differences between mechanochemically and thermally activated kaolins largely disappeared at later ages. (C) 2015 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2015

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The Effect of Alkali on the Properties of Limestone Calcined Clay Cement (LC3)

Wilasinee Hanpongpun, Karen Scrivener

The impact of alkali content on the properties of Limestone Calcined Clay Cement (LC3) was investigated in this study. KOH was added in order to increase the alkali content of the blended cements from 0.44% Na2Oeq to 1.21% Na2Oeq. The increase of alkali accelerates the degree of clinker hydration at 1 day but it slows down for later ages. Moreover, increasing alkalinity enhances the formation of carboaluminate phases at the early ages but the highest alkali content shows the smallest amount these phases at the later ages. The porosity decreases with increasing the percentage of alkali at 3 days but it is opposite at 28 days. The compressive strength can be boosted at early ages but there is loss gain strength at the later age for LC3-65 (2:1)-1.21% Na2Oeq.

Springer2018

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This paper reports the strength-promoting mechanism of alkanolamines on limestone-calcined clay cement (LC3). The hydration kinetics, phase formation and microstructure of LC3 with triethanolamine (TEA) or triisopropanolamine (TIPA) were investigated. TEA enhanced the strength of LC3, while TIPA was effective at 28 days, and a correct sulfate addition promoted their effects. Alkanolamines accelerated the aluminate reaction of LC3 during early hydration, increased sulfate slowed this reaction by producing more ettringite. TIPA favoured the hydration of ferrite in clinker, not only accelerated the silicate reaction of metakaolin, but also resulted in a rapid limestone reaction. Alkanolamines altered the morphology and chemical composition of the aluminate hydrates and C-A-S-H. Alkanolamines enabled the reduction of porosity of hardened pastes and the increased sulfate further refined them. It was the large pores being induced by TIPA at early ages that were considered to have an adverse impact on the early strength of LC3.

PERGAMON-ELSEVIER SCIENCE LTD2021

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