Measurement of the elastic properties of swelling clay minerals using the digital image correlation method on a single macroscopic crystal
Résumé
This paper presents a new methodology for determining the elastic moduli of swelling clay minerals based on the combination of two original elements: (a) a natural multi-millimetric vermiculite crystal considered as a model system of swelling clay minerals and (b) a mechanical device that allows for mechanical compression in a controlled hydric state while concomitantly measuring the resulting strain field using the digital image correlation (DIC) method. Following this approach, the DIC method can (a) identify anomalous areas of the strain field to be excluded from an elastic analysis and (b) not introduce any assumptions for Poisson's ratio, as often required in other techniques (e.g., nanoindentation).
This approach was applied to a vermiculite crystal, with dimensions of 5 x 5 mm(2) and a thickness of 1 mm; the value obtained for the undrained uniaxial Young's modulus was 323 +/- 3.9 GPa. To the authors' knowledge, this is the first value for Young's modulus proposed in the literature for a natural and pure swelling clay mineral and is consistent with those obtained from synthetic samples and molecular dynamics simulations.