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Publication Detail
Experimental Investigation of the Mechanical Properties of Magnesium Sulfate Hydrates: Implications for the Strength of Hydrated Deposits on Mars
  • Publication Type:
    Journal article
  • Publication Sub Type:
  • Authors:
    Grindrod PM, Heap MJ, Fortes AD, Meredith PG, Wood IG, Tripetta F, Sammonds PR
  • Journal:
    Journal of Geophysical Research
  • Issue:
  • Article number:
  • Status:
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We have carried out uniaxial compression experiments to determine the mechanical properties of three crystalline magnesium sulfate hydrates which may be present in the near-surface environment of Mars, specifically, kieserite (MgSO4·H2O), epsomite (MgSO4·7H2O), and meridianiite (MgSO4·11H2O). Our synthetic samples of kieserite, epsomite, and meridianiite have mean values of unconfined compressive strength of 6.3 ± 2.2 MPa, 12.9 ± 5.4 MPa, and 30.1 ± 15.6 MPa respectively, and Young’s Modulus of 0.8 ± 0.3 GPa, 2.9 ± 1.3 GPa, and 5.9 ± 2.6 GPa respectively. The mechanical properties of our synthetic specimens are controlled predominantly by the sample porosity; generally the strength increases as the porosity decreases. We were able to measure Poisson’s ratio in only 20 % of our tests, resulting in errors sufficiently large to preclude determination of a relationship with porosity. Although our tests cannot quantify any relationship between hydration state and mechanical properties, the different porosities produced by consistent sample preparation methods suggest that the addition of non cation-coordinated water molecules likely reduces the bulk strength of sulfate hydrates. We expect the mechanical properties of sulfate hydrate deposits on Mars to be governed by the bulk porosity, rather than the strength of the pure solid phase. We have also carried out preliminary cyclic stressing tests, replicating possible periodic depositional and erosional periods on Mars resulting from changes in obliquity. A gradual compaction and reduction in sample porosity, rather than increasing crack damage, is observed with each loading cycle. This suggests that the obliquity-related evolution of mechanical properties of similar deposits on Mars will depend on local factors such as bulk density, in addition to the overall stress history.
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