Influence of Anhydrite on the Properties and Microstructure …
The results show that adding an appropriate amount of anhydrite promotes the hydration of . The highest compressive strength is reached at an anhydrite content of 15 wt.%. As the …
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Petrographic Record and Conditions of Expansive …
Article, 2023. Hydration of anhydrite to gypsum (gypsification of anhydrite) in the weathering zone sometimes causes a volume increase. This can lead to local detachments of the surface layer of the weathering anhydrite rocks and …
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Gypsum hydration: a theoretical and experimental study
according to a through-solution route, first the hemihydrate dissolves and then the dihydrate precipitates from the solution. CaSO4 ⋅0.5H2O +1.5H2O →CaSO4 ⋅2H2O (1) ... the hydration speed varies during the hydration due to the formation and precipitation of gypsum. The measured hydration time is much shorter than value from /7/ with
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Anhydrite
In geologic history, anhydrite can convert to gypsum by absorbing water and changing its crystal structure. This process is called hydration. Anhydrite can also be converted to gypsum or lime by pressure and temperature. In terms of use, anhydrite has several applications.
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Solventless Mechanochemical Synthesis of Phase Pure …
Syngenite (K 2 Ca(SO 4) 2 ⋅ H 2 O) presents an effective hydration activator (accelerator) for anhydrite (CaSO 4) applied in construction systems.The current synthesis relies on co-precipitation of K 2 SO 4 and CaSO 4 ⋅ 2H 2 O and produces large amounts of waste water holding excess amounts of potassium sulfate. Therefore, this method is deemed ineffective, …
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The ternary system Portland cement–calcium …
Binders composed of ordinary Portland cement (OPC), calcium sulphoaluminate clinker (CSA) and anhydrite ( C S ¯ ) were examined in order to study the impact of variations of the OPC:CSA: C S ¯ ratio on the hydration process and related mortar properties. A first sample series had various anhydrite contents and fixed OPC to CSA ratio, and a second various OPC contents …
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Anhydrite Weathering Zone with Hydration Caves at …
Due to the exploitation of the gypsum, the anhydrite bed-rock was exposed on the quarry bottom. This action led to ongoing weathering, including anhydrite hydration under the inuence of precipitation and also surface and subsur-face water. In the weathering zone, the anhydrite hydration eaction r (CaSO 4 + 2H 2 O →CaSO 4 ·2H 2 O) takes place ...
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EGUsphere
This study assesses the influence of stress on hydration reaction kinetics and mechanics in experiments on anhydrite. We show that hydration occurs readily under stress and results in localized hydration along fractures and mechanic weakening. New gypsum growth is selective, and depends on the stress field and host anhydrite crystal orientation.
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Hydration of anhydrite of gypsum (CaSO 4.II) in a ball mill
The hydration of an anhydrite of gypsum (CaSO4.II) in a ball mill was studied as a function of time and temperature. The amount of gypsum formed at different intervals of time was determined by ...
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Dissolution and conversions of gypsum and anhydrite
In addition, the hydration and recrystallisation of anhydrite to gypsum can cause considerable expansion and pressures capable of causing uplift and heave. Sulphate-rich water associated with the ...
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Hemihydrate or waste anhydrite in composite binders with …
This indicated complete hydration of HH after 24 h, in agreement with [6]. Small peaks of anhydrite and calcite as remnants after the commercial gypsum manufacture are noted after 600 days, while quartz (SiO 2) was similarly present for the pastes with PFA.
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Dehydration Pathways of Gypsum and the …
Thermal expansion of γ-anhydrite is anisotropic being larger along the c axis. Within the 343-383 K thermal range, γ-anhydrite has been found to partially re-hydrate to bassanite CaSO4·0.5H2O. At 455 K the transformation γ …
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Effect of calcination temperature and superplasticizer on the
Figures 13, 18 indicated that significant anhydrite peaks were exhibited by APG7, APG8 and APG9 blended with a superplasticizer after 28 days of hydration. It was suggested that anhydrite hydration may have been hindered by the superplasticizer, particularly in APG subjected to high-temperature calcination.
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Anhydrite Weathering Zone with Hydration Caves at …
The abandoned gypsum quarry at Dingwall, in Canada, is a unique place with a peculiar "living" landscape created by expansive hydration of anhydrite process actively operating in the weathering zone at the quarry bottom. It causes a rapid volume
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Effect of anhydrite on hydration properties of mechanically …
In this paper, the effect of natural anhydrite on the hydration properties of calcium oxide-activated muscovite after mechanical activation was investigated. The mechanically activated muscovite was activated by two types of activators: calcium oxide and calcium oxide blended with natural anhydrite with contents ranging from 5%, 10%, and 15% ...
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(PDF) Gypse et Anhydrite
Le présent mémento est un panorama de l'activité extractive du gypse et de l'anhydrite à l'échelle française. Il présente un état des lieux des filières industrielles utilisant le ...
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Dehydration behaviors and properties of anhydrite II …
Excellent hydration properties of anhydrite II prepared at 280°C. Certain concentration H + can combine with the crystal water to form the H 3 O +, influencing the …
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Factors Influencing the Hydration, Dimensional Stability, and …
1. Introduction. Ordinary Portland cement–calcium sulphoaluminate cement–anhydrite (OPC-CSA-CS) ternary composite binders have the characteristics of a high early strength, rapid setting [], and adjustable rheological properties [], which make them suitable for use in repairing mortars, shrinkage-free grouting materials, cement-based self-leveling …
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SE
This study focuses on the influence of stress on hydration in the CaSO 4 • H 2 O system (Fig. 1a), specifically the hydration of anhydrite (CaSO 4, orthorhombic) to gypsum (CaSO 4 • 2H 2 O, monoclinic), as an analogue for …
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Calcium sulphate anhydrite based composite binders; effect …
1. Introduction. Calcium sulphate binders (CSB) based on hemihydrate or anhydrite are attractive due to their low CO 2 emissions and energy requirements. The production of hemihydrate from mineral gypsum requires calcination at less than 150 °C, while that of Portland cement (PC) requires 1450 °C, the latter also involves decomposition of CaCO 3 as the …
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Mechanochemical syngenite as hydration accelerator for anhydrite …
The degree of hydration of anhydrite paste was determined via thermal analysis performed by simultaneous TG-DSC measurements on a STA 409 PC Luxx instrument (NETZSCH-Gerätebau , Selb, Germany). Samples were prepared by dry blending in a 15 mL plastic tube 5 g of anhydrite binder with the respective quantities of potassium sulfate or ...
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(PDF) Rapid hydration and weakening of anhydrite under …
Hydration along fractures with a range of apertures up to 120 µm occurred in under 6 h. Once formed, gypsum-filled veins represent weak surfaces and are the locations of further …
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Effect of anhydrite on hydration properties of mechanically activated
At 30% calcium oxide and no anhydrite additions, the hydration products stratlingite and hydrotalcite, with the card number of 29–0285 (Ca 2 Al 2 SiO 7 ·8H 2 O) and 89–0460 ((Mg 0.667 Al 0.333)(OH) 2 (CO 3) 0.167 (H 2 O) 0.5), respectively, could be detected in MC paste after 3 d, which could not be detected for calcium oxide–anhydrite ...
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Dehydration Pathways of Gypsum and the Rehydration
The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the rehydration mechanism of soluble anhydrite was ...
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Solventless Mechanochemical Synthesis of Phase Pure …
anhydrite ( 2.7 g L 1 at 18 °C) in comparison to its hydration product gypsum (solubility 2.0 g L 1), its reaction with water is too slow and needs to be accelerated. For this purpose, simple K 2SO 4 is commonly blended into anhydrite at ~ 0.5-1.0 wt.-% to speed up hydration kinetics.[9] Previous works have demon-strated that the accelerating ...
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Hydration caves and cavities from the recent weathering …
Hydration of anhydrite to gypsum (gypsification of anhydrite) in the weathering zone sometimes causes a volume increase. This can lead to local detachments of the surface layer of the weathering anhydrite rocks and creation of the hydration cavities and rare hydration caves (or swelling caves; German: Quellungshöhlen) inside domes formed by the uplifted layer.
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Influence of Anhydrite on the Properties and …
The results show that adding an appropriate amount of anhydrite promotes the hydration of . The highest compressive strength is reached at an anhydrite content of 15 wt.%. As the anhydrite content increases, the 's compressive …
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Hydration mechanism of the ternary system Portland …
Hydration mechanism of the ternary system Portland cement – calcium sulphoaluminate clinker - anhydrite Ternary mixtures composed of ordinary Portland cement (OPC), calcium ...
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Calcium sulphate anhydrite based composite binders; …
Calcium sulphate anhydrite based composite binders; effect of Portland cement and four pozzolans on the hydration and strength J.I. Escalante-Garcia, O.A. Martínez-Aguilar, L.Y. Gomez-Zamorano PII: S0958-9465(16)30718-1 DOI: 10.1016/j.cemconcomp.2017.05.012 Reference: CECO 2834 To appear in: Cement and Concrete Composites Received Date: 14 ...
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The ternary system Portland cement–calcium
DOI: 10.1016/J.CEMCONCOMP.2010.03.010 Corpus ID: 138073520; The ternary system Portland cement–calcium sulphoaluminate clinker–anhydrite: Hydration mechanism and mortar properties
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