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The transition from weakening to strengthening in dehydrating gypsum: Evolution of excess pore pressures
Author(s) -
Ko Suzchung,
Olgaard David L.,
Briegel Ueli
Publication year - 1995
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/95gl00886
Subject(s) - embrittlement , gypsum , pore water pressure , materials science , dehydration , ductility (earth science) , ultimate tensile strength , hydration reaction , composite material , metallurgy , cement , chemistry , geotechnical engineering , creep , geology , biochemistry
Dehydration reactions can induce excess pore‐fluid pressures that are high enough to affect the mechanical strength and ductility of rocks. Laboratory experiments have been conducted to investigate this phenomenon in dehydrating rocks with porosities that are initially negligible but increase as the reaction progresses. Polycrystalline gypsum samples were first heated under pressure to induce dehydration, then axially loaded after different amounts of reaction. Within the first 1% of reaction, the ultimate strength of the sample decreased and embrittlement was observed. The ultimate strength recovered within 3% of reaction and eventually exceeded that of pure gypsum. Our results indicate that the initial weakening and embrittlement correspond to a pulse of excess pore pressure in the sample interior. Subsequent strengthening is caused by a decrease in pore pressure and the higher strength of the product phase.