##tihuan2##An important aspect of the anhydrite hydration in the different varieties of secondary gypsum is that the geological process occurs without any modification of the lithofacies indicating that the process usually operates in an isovolumetric mode. ... that determines the rate or speed of the delayed elasticity, is ... concluded that the ...
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##tihuan2##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 …
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##tihuan2##This study assesses the influence of stress on hydration reaction kinetics and mechanics in experiments on anhydrite. We show that hydration occurs readily …
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##tihuan2##Due to the advantages of high early strength and rapid setting, ternary systems consisting of ordinary Portland clinker (OPC), calcium sulphoaluminate (CSA) clinker, and anhydrite have broad application prospects. However, further studies need to be undertaken to find a more optimal mixing proportion of this ternary binder in order to …
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##tihuan2##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 …
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##tihuan2##To better understand the hydration of slag, various combinations of slag–anhydrite–lime were investigated, mainly by conduction calorimeter. Compressive and bending strength were also measured. The following conclusions were obtained: in the case of existing calcium hydroxide (Ca(OH)2), hydration products were …
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##tihuan2##In this paper the hydration behavior of ye'elimite-anhydrite pastes, with and without PCE, was studied. The morphology of ettringite, as well as the hydration and microstructural evolution of the pastes were studied by means of various investigation techniques. ... Large cracks (several microns or larger) showed up at ~7 d (Fig. 8 e and f ...
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##tihuan2##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 ...
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##tihuan2##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 …
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##tihuan2##Additional experiments indicated that upon anhydrite addition, the chemically bound water content in C-3 increased by 3.12 % at 6 h, accompanied by a widened half-peak width and a deeper decomposition valley for AFt, supporting the notion that anhydrite accelerates C-3's early hydration kinetics within 6 h, in accordance with previous ...
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##tihuan2##Also using a dead weight approach, Keulen et al. [70] reported hydration of anhydrite to form gypsum, causing expansion against stresses of up to *11 MPa. However, by far the largest stresses ...
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##tihuan2##The influence of calcined alum on the hydration process,the structure and intensity of hardened anhydrite,the degree of solution supersaturation,and other properties are investigated by determining setting time,hydration rate and hydration temperature increases in combination with analyzing the microstructure and intensity of hardened …
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##tihuan2##The swelling of clay-sulfate rocks is a well-known phenomenon often causing threats to the success of various geotechnical projects, including tunneling, road and bridge construction, and geothermal drilling. The origin of clay-sulfate swelling is usually explained by physical swelling due to clay expansion combined with chemical swelling associated with the …
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##tihuan2##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 ≥ …
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##tihuan2##The performance of mechanochemical syngenite applied as hydration accelerator for fully formulated anhydrite-based self-levelling floor screeds was evaluated regarding workability (open time ...
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##tihuan2##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, …
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##tihuan2##Anhydrite rock, composed mainly of CaSO 4, possesses unique engineering properties, particularly its significant expansion behavior upon exposure to water.This expansion tendency profoundly impacts the stability of tunnel openings and slope engineering. Upon contact with water, anhydrite rock undergoes hydration reactions, …
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##tihuan2##As a plasticizer and retarder, calcium lignosulfonate (CL) frequently leads to quick set of Portland cement containing anhydrite.For exploring the cause of this problem, the hydration characteristics of the tricalcium aluminate–anhydrite system in the saturated calcium hydroxide solution with and without CL were researched from two aspects: the …
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##tihuan2##This paper reports the physical properties and hydration products of slag cement that was prepared by activating ground granulated blast furnace slag with commercial lime and plaster of Paris (POP) as activators. The consistency, setting times and soundness of various mixes of slag-lime-POP is reported. The hydration products …
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##tihuan2##OPC/CSA ratios on the hydration products and strength development have been inves-tigated in some research works. With regard to the hydration products, it was reported that [1,28] when the OPC proportion in ternary composite systems is lower than 40%, C4A3S is given priority in the hydration process. In the absence of OPC, ettringite is formed
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##tihuan2##The hydration rate is used to judge the hydration efficiency of anhydrite. From Fig. 3 d, the hydration efficiency of anhydrite increases initially and then decreases …
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##tihuan2##The major objective of applying an accelerator is to speed up hydration sufficiently in order to gain increased early strength without decreasing final strength. In Europe, floor screeds are categorized according to their final (28 d) compressive strength as outlined in the DIN EN 13454–1 standard where the classes C5, C7, C12, C16, C20, …
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##tihuan2##andanhydriteparticles contains up to millimetre-scale clasts with intense internal fracturing low gypsum content. The amount of gypsum is difficult to identify from the images, as …
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##tihuan2##hydration reaction (0.186 for both α- and β-hemihydrate). The microstructure change during the hydration was investigated using ultrasonic method because the ultrasonic sound speed varies in different structures. Figure 2 shows the measured β-hemihydrate hydration results with the water/hemihydrate ratio of 0.65.
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##tihuan2##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 …
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##tihuan2##The effect of K2SO4 activator on the hydration of chemical anhydrite obtained from burned FGD-gypsum has been studied by different experimental techniques.
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##tihuan2##(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.
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##tihuan2##Rapid hydration and weakening of anhydrite under stress: Implications for natural hydration in the Earth's crust and mantle ... Hydration along fractures with a range of apertures up to 120 µm occurred in under 6 hours. Once formed, gypsum-filled veins represent weak surfaces and are the locations of further shear fracturing, brecciation ...
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##tihuan2##However, a higher addition of anhydrite can retard the main peak of hydration despite promoting the intermediate peak and improving the hydration reaction …
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