Experimental analysis of crystal growth in anhydrite and its impact on swelling quantification

This study focuses on the investigation of the chemical reactions involved in the phenomenon of anhydrite swelling, that is a well-known issue that may affect the functionality of underground infrastructures.

The study was performed on Triassic gypsum and anhydrite samples collected from an Alpine location (Signols, Oulx in the Susa Valley, Piedmont, Italy) and involved the investigation of the behavior of this material immersed in different aqueous solutions at various temperatures.

The influence of different aqueous solutions (distilled water, water with CaSO₄, water with MgCl₂, and water with NaCl)  on the solubility and precipitation of new crystals was evaluated at different temperatures (15°C, 40°C, and 60°C).

Both macro- and micro-scale observations were conducted before water immersion and after different time intervals. Macro-scale observations included the measure of the volume and the mass and the capture of photographical images with a camera. Micro-scale analyses involved the use of SEM-EDS to determine the mineralogical composition and examine the changes in micro-scale morphological features (e.g., growth of new crystals).

The experiment seeks to identify potential mineralogical transformation, particularly the hydration of anhydrite into gypsum, under the specified conditions. The findings will contribute to understanding the mechanisms influencing anhydrite swelling and its implications for geological and engineering applications.