Test Study on the Expansional Properties of Regenerated Anhydrite Rock

Xu, Chongbang; Zhang, Yajun; Yan, Junjie

doi:10.1088/1755-1315/330/4/042004

Cited by 2 publications

(3 citation statements)

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“…In this test, the highest free expansion rate is 10.55%; it is found that gypsum rock does not belong to the expansive rock compared with most expansion classification standards, which is obviously contrary to the existing research [16,17,28,39]. At the same time, in the free expansion rate test, it was found that the gypsum rock powder occurred to harden, as shown in Figure 9; the upper anhydrite in the graduated cylinder hydrated into gypsum and hardened, resulting in a weakened reaction between the lower anhydrite and water, which in turn decreased the free expansion rate of gypsum rock.…”

Section: Expansion Characteristic Indexcontrasting

confidence: 86%

“…At present, expansive rocks are divided into two categories [13][14][15][16][17][18]: the first one is caused by chemical expansion reaction, the mechanism is complex, and the time is long (such as anhydrite and glauberite); the second one is caused by hydrophilic minerals, and the expansion of this type of rock is cyclically reciprocated under the action of water absorption and loss (such as mudstone and tuff) [19]. The main indicators for judging the expansion potential of expansive rocks include water content [20][21][22], viscous material content [9,15,[23][24][25], free expansion rate [25], ultimate expansion rate [26], dry saturated water absorption rate [27], and ultimate expansion force [9,25].…”

Section: Introductionmentioning

confidence: 99%

“…Ma et al [29] analyzed the effect of CaSO 4 •H 2 O composition on four different gypsum rocks; it was found that the higher the content of CaSO 4 •H 2 O composition, the lower the strength and energy change of gypsum rocks, but the larger the microscopic size of rock samples. Xu et al [16] studied the expansion characteristics of rerigid gypsum rock and found that its maximum expansion rate in a short time was 2.6%. Wu [18] conducted a short-term laboratory test to analyze the expansion characteristics of the remolded gypsum rock.…”

Section: Introductionmentioning

confidence: 99%

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Study on Expansion Characteristics and Expansion Potential of Gypsum Rock

Zhu

et al. 2022

Geofluids

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In this study, the relationship between four expansion indices and the expansion potential of gypsum rock was studied; on this basis, a criterion for judging expansion potential is established for gypsum rock. The results show that the free expansion rate is unsuitable for grading gypsum rocks’ expansion potential. Setting the gypsum rock in the Wuzhishan tunnel as the research subject, the ultimate expansion rate is 24.28% on the 7th day and 34.08% on the 30th day; the ultimate expansion rate on the 7th day of the indoor rock sample can be estimated by the fitting formula on the 30th day, the ultimate expansion force is 304.51 kPa, and the BET-specific surface area is 6.31 m2/g. The ultimate expansion ratio and BET-specific surface area have an excellent linear relationship with the ultimate expansion force. Setting the ultimate expansion force, ultimate expansion ratio and BET-specific surface area as the standard, the criterion for judging the expansion potential of gypsum rock is determined, which is more convenient and accurate than existing standards. The standard in this paper can predict the potential disasters that may occur in underground engineering.

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Section: Expansion Characteristic Indexcontrasting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Study on Expansion Characteristics and Expansion Potential of Gypsum Rock

Zhu

et al. 2022

Geofluids

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Rapid hydration and weakening of anhydrite under stress: implications for natural hydration in the Earth's crust and mantle

Heeb,

Healy,

Timms

et al. 2023

Solid Earth

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Abstract. Mineral hydration is an important geological process that influences the rheology and geochemistry of rocks and the fluid budget of the Earth's crust and mantle. Constant-stress differential compaction (CSDC) tests, dry and “wet” tests under confining pressure, and axial-stress tests were conducted for the first time to investigate the influence of triaxial stress on hydration in anhydrite–gypsum aggregates. Characterization of the samples before and after triaxial experiments was performed with optical and scanning electron microscopy, including energy-dispersive spectroscopy and electron backscatter diffraction mapping. Stress–strain data reveal that samples that underwent constant-stress differential compaction in the presence of fluids are ∼ 14 % to ∼ 41 % weaker than samples deformed under wet conditions. The microstructural analysis shows that there is a strong temporal and spatial connection between the geometry, distribution, and evolution of fractures and hydration products. The increasing reaction surface area in combination with pre-existing gypsum in a gypsum-bearing anhydrite rock led to rapid gypsification. The crystallographic orientations of newly formed vein gypsum have a systematic preferred orientation for long distances along veins, beyond the grain boundaries of wall-rock anhydrite. Gypsum crystallographic orientations in {100} and {010} are systematically and preferentially aligned parallel to the direction of maximum shear stress (45∘ to σ1). Gypsum is also not always topotactically linked to the wall-rock anhydrite in the immediate vicinity. This study proposes that the selective inheritance of crystal orientations from favourably oriented wall-rock anhydrite grains for the minimization of free energy for nucleation under stress leads to the systematic preferred orientation of large, new gypsum grains. A sequence is suggested for hydration under stress that requires the development of fractures accompanied by localized hydration. 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 fracturing, brecciation, and eventual brittle failure. These findings imply that non-hydrostatic stress has a significant influence on hydration rates and subsequent mechanical strength of rocks. This phenomenon is applicable across a wide range of geological environments in the Earth's crust and upper mantle.

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Test Study on the Expansional Properties of Regenerated Anhydrite Rock

Cited by 2 publications

References 1 publication

Study on Expansion Characteristics and Expansion Potential of Gypsum Rock

Study on Expansion Characteristics and Expansion Potential of Gypsum Rock

Rapid hydration and weakening of anhydrite under stress: implications for natural hydration in the Earth's crust and mantle

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