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 shear...
(1973) performed experiments to estimate anhydrite and gypsum solubilities in aqueous and NaCl solutions at dif-ferent temperatures and pressures up to 1,000 bars. Based on their own experimental results and on experimental data found in the literature, they proposed empirical equations for the determination of anhydrite and gypsum solubilities.
Meanwhile, the accelerated hydration of C 3 A can speed up the depletion of calcium sulfate, ... From Fig. 3 (a) (without TEA), it can be seen that anhydrite is the main calcium sulfate in cement. During cement hydration process, …
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 …
The activators K 2 SO 4 and Na 2 SO 4 had a large effect on the hydration of anhydrite binder at its early age (up to 3 days) ... During the hydration of the anhydrite binder obtained at a temperature of 500 °C and using both 1% and 2% of the activator K 2 SO 4, syngenite was recorded after 10 min (Figure 6 a,b). Meanwhile, during hydration of ...
comprehensive considerations of strength, speed‐up hydration, and to improve microstructure. ... K2SO4 and Na2SO4 were used as activators to accelerate the hydration and hardening of anhydrite ...
At lower temperatures, the hydration speed of anhydrite is much higher and a slow hydration of pure anhydrite can be observed. Diagram 3 - Heat of hydration of hemihydrate ... Before and after the peak. Up until the peak of heat evolution, the crystal growth of gypsum is the main influencing factor because there is enough hemihydrate left to ...
Experimental calcination has shown that T of up to ∼ 1000 °C can be reached in traditional gypsum kilns [2], [8], ... exploration range of 3 to 60 °2θ and goniometer speed of 0.05 °2 ... Delayed anhydrite II hydration was the cause of low strength and weathering resistance in plasters prepared with gypsum calcined at T ≥ 300 °C, but ...
The Hydration of Anhydrite. Marie Farnsworth; Cite this: Ind. Eng. Chem. 1925, 17, 9, 967–970. Publication Date (Print): September 1, 1925. Publication History. ... These metrics are regularly updated to reflect usage leading up to the last few days. Citations are the number of other articles citing this article, calculated by Crossref and ...
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 also studied by Monte Carlo (MC) simulations. The thermodynamic calculation results reveal that the dehydration mechanism of gypsum significantly depended …
The application of hydrothermal treatment to speed up the hydration resulted in formation of a hydrogarnet . Crystallographic studies [ 5, 6 ] indicate that there is no close structural relationship between gehlenite (crystallizing in the tetragonal system [ 1 ]) and the so-called gehlenite hydrate.
It was found that pure syngenite promotes the hydration of anhydrite more strongly than equimolar amounts of K₂SO₄, leading to a high degree of hydration, reduced setting …
Morphology and origin of anhydrite hydration caves and cavities are presented. • The caves develop due to expansive gypsification of anhydrite in the weathering zone. • Caves form within domed and tepee-like landforms growing at the quarry bottom. • Hydration caves reach length up to 8.87 m and height up to 1.35 m. •
Anhydrite exists in different polymorphs (anhydrite I-III) of which anhy- ... which strongly influence hydration, it is very important to be able to characterize the sulphate carrier composition in the cement and in applications with high ... was performed in chamber furnaces at 85 °C up to 550 °C in air. The initial high purity gyp-
During cement hydration process, anhydrite is. ... TEA seems to speed up the hydration of C 3 A but slows down the hydration of C 3 S (Han et al. 2015; Ramachandran 1996). According to Fig. 5(a ...
The performance of mechanochemical syngenite applied as hydration accelerator for fully formulated anhydrite-based self-levelling floor screeds was evaluated regarding workability (open time ...
Besides, a greatly accelerated setting phenomenon was found for cement paste prepared at intermediate mixing speed with TEA dosage of 0.2 wt% and the further increased mixing speed can eliminate this abnormal setting performance, which could be caused by the first decreased and then increased dissolution rate of anhydrite along with the ...
The variation of the amount of gypsum formed and the specific surface area developed during the hydration of anhydrite with hydration time are given in Fig. 2.The amount of gypsum first increases slowly and then appears at a faster rate (Fig. 2a).The rate of formation of gypsum with hydration time is shown in Fig. 2b.The curve shows that the rate first increases …
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 …
At lower temperatures, the hydration speed of anhydrite is much higher and a slow hydration of pure anhydrite can be observed. Diagram 3 - Heat of hydration of hemihydrate ... Before and …
Hydration of anhydrite
The results of XPS analysis suggested that the concentration of the salt when metal cations could be detected by XPS analysis in the product of anhydrite hydration equaled to the one when it …
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 ...
Hydration - This involves the addition of water to minerals, causing them to swell and eventually break apart. An example is the hydration of anhydrite (CaSO4) to form gypsum …
gypsum-anhydrite conversion is considered in detail elsewhere in this chapter. The 4.1.6 Figure 2B shows the solubility data for anhydrite and gypsum in their stability regions. The solubility of ...
Activator solutions speed up the time for the appearance of maximum specific surface area and the rate of formation of maximum gypsum. ... The hydration of an anhydrite of gypsum (CaSO4.II) in a ...
The speed of lateral growth of the hydrating anhydrite layers, which are now the floors of the quarry abandoned in 1956, has been systematically measured and estimated at ca. 2 cm/year, similar to the values recorded in Europe, in the similar caves …
In the Dingwall gypsum quarry in Nova Scotia, Canada, operating in 1933–1955, the bedrock anhydrite deposits of the Carboniferous Windsor Group have been uncovered from beneath the secondary gypsum beds of the extracted raw material. The anhydrite has been subjected to weathering undergoing hydration (gypsification), transforming into secondary …
The activators K2SO4 and Na2SO4 had a large effect on the hydration of anhydrite binder at its early age (up to 3 days) in comparison with the anhydrite binder without activators.
increase the hardening speed. This article deals with the effects of calcium sulfate (anhydrite) percentage on ... (anhydrite) percentage on hydration mechanisms, compressive strength and dimensional stability of binders containing 40% OPC. Calcium sulfate quantity is an essential parameter that can be used to control the hardening speed and ...
The activators K2SO4 and Na2SO4 had a large effect on the hydration of anhydrite binder at its early age (up to 3 days) in comparison with the anhydrite binder without activators.
This is because gypsum, the hydration product of anhydrite, is extremely easy to dehydrate and forms hemihydrate in regular environments . Additionally, it should be ... research works performed up to now have mainly focused on OPC-CSA binary systems. ... mixing at low speed for 30 s was applied to minimize the amount of air trapped in the ...
The hydration of an anhydrite of gypsum ... The CaSO 4.II phase of anhydrite is the one that is thermodynamically stable up to 1180 °C and occurs naturally as the mineral anhydrite. It may also be produced by high-temperature (≈600 °C) calcinations of natural or by-product gypsum. Under ambient conditions, CaSO4.II reacts very slowly with ...
Sievert et al. (2005) proposed a five-step mechanism of hydration via solution–precipitation: (i) rapid initial partial dissolution of CaSO 4 and adsorption of hydrated Ca 2+ and SO 4 2-ions at the surface of anhydrite, (ii) …
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 anhydrite-based cementitious material. International researchers have previously conducted on the relationship model between pore structure and compressive strength, but there have been few ...
A concept for the hydration mechanism of anhydrite particles developed by Sievert et al. (2005) involves dissolution and precipitation, which was adapted here to explain hydration of the Òdena anhydrite under stress (Fig. 8). The wet-mode experiments make H 2 O groups available to new mineral interfaces during the initial intra-granular fracturing
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 strength decreases. ... and the beaker was stirred at a constant speed, maintained at 215 r/min. After most of ...