Permeability of gypsum samples dehydrated in air
Olgaard et al. (1995) discussed the influence of gypsum dehydration reaction and solid volume reduction on permeability under different temperatures (23-150 °C), different confining pressures ...
Experimental Study on Physical and Mechanical Properties of Gypsum …
In order to study the physical and mechanical properties of gypsum rock samples in three states (natural, high-temperature dehydration and hydration time), natural gypsum rock was put into high-temperature condition of 220°C for dehydration treatment, and then the high-temperature dehydrated gypsum rock was treated with different hydration time, and the …
Dehydration‐induced damage and deformation in …
Dehydration of gypsum in drained conditions induces a decrease in Vp and Vs Acoustic emissions indicate pore collapse Poisson's ratio decreases due to microcracks and solid phases replacement ... At standard …
Permeability of gypsum samples dehydrated in air
An interplay between reaction progress and rock permeability becomes evident when one compares the molar volumes [e.g., Deer et al., 1992] of the educt and solid products involved in the transformation of gypsum (74.53 cm 3 /mol) to bassanite (53.17 cm 3 /mol) and anhydrite (45.68 cm 3 /mol), respectively. One notices that, at ambient conditions, the solid …
Geochemical reactions and pore structure analysis of anhydrite/gypsum
Minor changes in specific surface area and total pore volume for anhydrite and halite are observed. Abstract. ... These results confirm that the process of gypsum dehydration is mainly derived by temperature, and usually takes place in the long term. In summary, the XRD results indicate a high level of stability of halite, anhydrite, and gypsum ...
The pressure dependence of the dehydration of gypsum …
KEYWORDS: gypsum, bassanite, dehydration. Introduction THE present paper deals with the experimental determination of P-T data for the metastable dehydration reaction involving the …
Structural evolution during the dehydration of gypsum …
(a) Unit-cell volume of the hemihydrate phase during the dehydration study of pure gypsum within a sealed capillary with an excess of water. (b) View of the ab plane of the hemihydrate structure with 0.5 water molecules content at 230ºC.
Structural evolution during the dehydration of gypsum …
F IG.4.(a) Unit-cell volume of the hemihydrate phase during the dehydration study of pure gypsum within a sealed capillary with an excess of water. ( b ) View of the ab plane of the hemihydrate ...
(PDF) Dehydration Pathways of Gypsum and the …
The thermodynamic calculation results reveal that the dehydration mechanism of gypsum significantly depended on ambient temperature and water vapor pressure.
Raman spectroscopy of the dehydration process of …
gypsum, filling approximately one-third of the crucible volume. The crucibles were then put into a digital convection oven capable of setting up the designated heating regimes.
Structural evolution during the dehydration of gypsum …
The dehydration of pure and waste gypsums has been examined using in situ synchrotron angledispersive X-ray diffraction. Pure gypsum was studied under a number of defined …
Fast in-situ X-ray scattering reveals stress sensitivity of gypsum
The gypsum-hemihydrate transformation has been long studied as a laboratory analogue for seismogenic dehydration reactions during subduction 8,9 and as a model of metamorphic dehydration reactions ...
From atom level to macroscopic scale: Structural mechanism …
Plaster, made of calcium sulfate hemihydrate (CaSO 4 •½H 2 O) and/or γ-anhydrite (CaSO 4) is obtained by dehydration of gypsum (CaSO 4 ·2H 2 O) at 100–200 °C. When …
Gypsum: a review of its role in the deterioration of
The dissolution of gypsum in water occurs with a volume contraction of the system while its precipitation results in an expansion (as is the case for most soluble salts); 3. The dehydration of gypsum to hemihydrate in solution results in an expansion; and, 4.
Understanding gypsum in 3 diagrams
Diagram 1 - Dehydration. The first process is the formation of hemihydrate or anhydrite from dihydrate. To obtain more information about this step, gypsum crystals were grown from sodium sulphate and calcium chloride via a diffusion process. A large test tube, approximately 200mL in volume, was filled with 3g of sodium sulphate (Na 2 SO 4).
From atom level to macroscopic scale: Structural mechanism of gypsum
The dehydration of gypsum (CaSO4·2H2O) into calcium sulfate hemihydrate (CaSO4·0.5H2O) and anhydrites (γ-CaSO4andβ-CaSO4) was carried out by heating under a constant pressure of water vapor ...
Dehydration Pathways of Gypsum and the …
In this work, the dehydration pathways of gypsum and the rehydration mechanism of soluble anhydrite were mainly investigated by thermodynamic modeling and MC simulations. The dehydration pathways of …
Thermo-poro-mechanics Modelling of Gypsum …
Thermo-poro-mechanics Modelling of Gypsum Dehydration 179 1 mol of gypsum Intact Gyp- sum Sample 1 mol of bassanite porosity 1.5 mol of water Reaction products excess Expelled w ater Fig.1. Illustration of the reaction (1) of gypsum into bassanite and water after a temperature increase up to 388oK. 1mol of Gypsum (molar volume 74.69cm3 mol−1)
Dehydration-induceddamageanddeformationin
34 induce a negative solid volume change since the dehydration products are denser than ... 75 tests were complemented by in situ observations of gypsum dehydration in an environ-
Raman spectroscopy of the dehydration process of gypsums …
The dehydration process of a synthetic gypsum indicates that it has an interstitial gypsum phase dehydrating in a similar way to the interstitial phase found in the Terra Alba gypsum.
Experimental study of the dehydration reactions gypsum …
The system Ca S O 4 – H 2 O , characterized by the three dehydration reactions gypsum-anhydrite, gypsum-bassanite, and bassanite-anhydrite, was reexamined by in situ differential pressure analysis in the temperature range of 60 – 350 ° C up to 3.5 GPa pressure. The investigation revealed a fine structure in the dehydration boundaries of gypsum-bassanite …
Dehydration-induced damage and deformation in gypsum and implications for subduction zone processes
Calcium sulphate dihydrate (CaSO4·2H2O or gypsum) is used widely as building material because of its excellent fire resistance, aesthetics, and low price. Hemihydrate occurs in two …
Pore formation during dehydration of polycrystalline …
dehydration of gypsum is an anomalously slow process compared to the dehydration of other compounds containing crystal water (Charola et al., 2007). ... Because the fluid volume (Vfluid) ...
Gypsum: A review of its role in the deterioration of
Gypsum dehydration occurs in two separate steps: i) in the ... The volume increase due to the formation of the gypsum from calcite is the major cause of the development of cracks in the carbonate ...
Thermal properties and microstructure of gypsum …
4 is formed during gypsum dehydration, which was also confirmed by Kuntze [4] and Paulik et al. [5]. The effect of experimental conditions such as temperature, pressure, ... Schematic diagram of the volume composition of the gypsum system. (a) Before dehydration (dihydrate); (b) upon first dehydration step (hemihydrate); and (c) upon second ...
Formation of α-Hemihydrate Inside of a …
Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials in the world. During calcination, calcium sulfate subhydrates are formed and, for technical reasons, are mixed with water to …
In situ IR spectroscopic and thermogravimetric study of …
dehydration products of gypsum. Of particular interest in our context is the work of Bensted and Prakash (1968) who investigated the possibility of the existence of two forms of hemihydrate (c~ and/3), but concluded that there are only three dehydration products of the dehydration of gyp-
The dehydration kinetics of gypsum at high pressure and …
An in situ dehydration kinetics study of gypsum under water-saturated condition was performed in the temperature and pressure ranges of 383–423 K and 343–1085 MPa by using a hydrothermal diamond anvil cell and Raman spectroscopy. Kinetic analysis shows that the dehydration rate k increases with pressure, suggesting a negative pressure dependence on dehydration rate. …
Temperatures (ºC) at which key events occur during the dehydration …
Gypsum plaster is an inorganic binder that is prepared in a two-step process. The first step is dehydration: heated to 100-200 • C, gypsum (CaSO 4 ⋅2H 2 O) releases water as vapor [1, 2] and ...
The dehydration process of gypsum under high pressure
The effects of pressure on the dehydration of gypsum materials were investigated up to 633 K and 25 GPa by using Raman spectroscopy and synchrotron X-ray diffraction with an externally heated diamond anvil cell. At 2.5 GPa, gypsum starts to dehydrate around 428 K, by forming bassanite, CaSO4 hemihydrate, which completely dehydrates to γ-anhydrite at 488 K. …