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
tration of anhydrite does not provide reliable results at temperatures below 70 C, as the results had to be extrap-olated in this region. Marsal (1952) studied the influence of the …
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 …
The influence of sodium sulfate on the anhydrite hydration process and the crystal morphology of its dihydrate products were studied by the determination of the hydration rate, hydration temperature and the ion concentration in liquid phase, in combina-tion with the investigation of the microstructure of the hardened anhydrite paste. Moreover, the …
Increasing the number of water channels was critical to enhance the hydration activity of HPG compared with the hydration reactivity of industrial HPG and type-α high-strength gypsum. ... and calcium sulfate anhydrite [7]. It is crucial to effectively regulate the crystallization process and to prepare gypsum with controlled crystal …
The paste hydration of brownmillerite with and without gypsum: a time resolved synchrotron diffraction study at 30, 70, 100 and 150 °C. Journal of Materials Chemistry, 2004. ... F. Winnefeld, and B. Lothenbach, The ternary system Portland cement–calcium sulphoaluminate clinker–anhydrite: Hydration mechanism and mortar …
In previous studies on anhydrite hydration, researchers have found that the strength of the hardened material correlates with the rate of formation of intergrown and connected gypsum crystals [22,50]. In anhydrite floor screeds, the process of gypsum formation involves the dissolution of anhydrite, the formation of dihydrate nuclei and …
At the same time, anhydrite will combine with Al 2 O 3 in slag to form ettringite [11] and CSH [12] to improve hydration and hardening characteristics of …
Aluminophosphate cement () is a new type of hydraulic cementitious material with many potential functions. Microscopic analysis techniques were used to study the effect of anhydrite on the performance and hydration process of under standard curing conditions. The results show that adding an appropriate amount of anhydrite …
This paper reported a successful preparation of CaCO 3 /anhydrite composites of anhydrite coated with nanosized CaCO 3 by chemical precipitation route using the Ca(OH) 2 –H 2 O–CO 2 reaction system. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron …
The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the rehydration mechanism of soluble anhydrite …
Hemihydrate or waste anhydrite in composite binders with blast-furnace slag: Hydration products, microstructures and dimensional stability ... (SEM). Hydration processes of all samples were observed by the hydration heat. It was observed that the optimal proportions of FGD gypsum, cement, and mineral powder were 75%, …
The heat of hydration of the anhydrite was calculated in the same way. Again, the heat of hydration determined experimentally for the tested sample was compared with that calculated, on a theoretical basis, for the calcium sulphate hemihydrate. The value of the * Permanent address: The National Research Center, Dokki, Cairo, …
The reactivity of these cements depends on the composition of the clinker and on the type and amount of calcium sulfate added [6], [7], but the main hydration product at early ages is the formation of crystalline ettringite and nanocrystalline hydrated aluminum hydroxide [8] due to the reaction of ye'elimite with anhydrite and water, …
These uncertainties regarding the phase diagram of CaSO 4 have hampered the search for a large-scale synthesis route for bassanite at a lower temperature, and thus lower environmental cost ...
When too high an amount of hemihydrate is present, it simply follows its own hydration route towards gypsum precipitation, leading to an early setting of cement.
What is Anhydrite? Anhydrite is a fascinating mineral with a rich history and a variety of uses. Let's dive into some interesting facts about this unique substance.. Chemical Composition: Anhydrite is composed of calcium sulfate (CaSO4) without any water molecules, unlike its close relative gypsum, which contains water.. Crystal …
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 …
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 …
Excellent hydration properties of anhydrite II prepared at 280°C. Abstract. Certain concentration H + can combine with the crystal water to form the H 3 O +, influencing the stability of the crystal water in dihydrate so that can be completely removed under lower temperature. Therefore, this paper introduces a method wherein sulfuric …
Hemihydrate takes place hydration reaction immediately after mixing with water according to a through-solution route, first the hemihydrate dissolves and then the dihydrate …
Aluminophosphate cement () is a new type of hydraulic cementitious material with many potential functions. Microscopic analysis techniques were used to study the effect of anhydrite on the performance and hydration process of under standard curing conditions. The results show that adding an appropriate amount of anhydrite promotes …
They found that hydration reactions are retarded by the addition of citric acid. Ettringite and monosulfoaluminate were all detected as early hydration products. The influence of citric acid as a retarder for ternary binders based on Ordinary Portland Cements (OPC), CSA and anhydrite was investigated by Winnefeld et al. [6]. Their main ...
Anhydrite [CaSO 4] is a common mineral that crystallizes, among other settings, in hydrothermal ore deposits and geothermal systems.Hydrothermal anhydrite can be a good host for primary and secondary fluid inclusions. It is also potentially a problematic host because of (1) its relatively high, and typically retrograde, solubility in most aqueous …
• Trial oral hydration whenever possible . • Avoid use of medications that require IV bags when possible (e.g., antibiotics, electrolytes). • Consider whether the patient is appropriate for non-invasive monitoring. Arterial lines require IV saline bags for circuit priming and pressurization. Surgical Services
Due to the very gradual hydration of anhydrites and their very low strengths, modification of the properties of anhydrite by a suitable external exciter was resolved within the work. The experimental work was conducted on natural anhydride, and as possible exciters for hydration, the following products were selected and tested: water-free sodium sulphate; …
This article is cited by 5 publications. Davide Mombelli, Danilo Luvizotto Gonçalves, Carlo Mapelli, Silvia Barella, Andrea Gruttadauria. Processing and Characterization of Self-Reducing Briquettes Made of Jarosite and Blast Furnace Sludges.
The performance of mechanochemical syngenite applied as hydration accelerator for fully formulated anhydrite-based self-levelling floor screeds was evaluated regarding workability (open time ...
The strength, hydration products, microstructure and heat of early hydration were investigated on alternative hydraulic green cements based on calcium sulphate anhydrite partially blended with Portland cement and pozzolans.Four pozzolans of different physical and chemical nature, namely a geothermal waste, silica fume, metakaolin and …
Excellent hydration properties of anhydrite II prepared at 280°C. Abstract. Certain concentration H + can combine with the crystal water to form the H 3 O +, influencing the stability of the crystal water in dihydrate so that can be completely removed under lower temperature.
Semantic Scholar extracted view of "The Hydration of Anhydrite." by M. Farnsworth. Skip to search form Skip to main content Skip to account menu. Semantic Scholar's Logo. Search 213,524,950 papers from all fields of science. Search. Sign In Create Free Account. DOI: 10.1021/IE50189A037;
In Fig. 9, the characteristic peak near 25.4° of anhydrite weakened significantly, and Table 3 shows a hydration rate reaching 78.5 %. These findings …
The increase of anhydrite from 5 % to 10 % led to a faster hydration reaction at the early stage, but lowered the proportion of ettringite at the later stage. From the SEM images in Fig. 19 (b), more anhydrite and less Ca(OH) 2 were observed at the early hydration stage.
The dehydration products of gypsum under different temperature and water vapor pressure were investigated by …
The long-term hydration of a mix with and without gypsum addition was investigated at 10, 23 and 40 °C by QXRD analysis.In addition, thermodynamic modelling was performed on all systems using GEMS to determine the stable phase composition and the influence of water loss during hydration. The results show that the formation of …
The source of this high Na concentration might have been leaching ofNa (with K) from anhydrite during hydration since the relict anhydrite zone has relatively higher Na and K than the bulk of the gypsum. In contrast, Sr con- centrations are notably constant throughout the sec- tion. However, the petrography shows that the bulk of Sr in gypsum ...
