Deterioration of volcanic tuff rocks from Armenia: constraints on salt crystallization and hydric expansion

Volcanic tuffs are widely used in the Armenian architecture and represent building stones of the country’s most precious cultural heritage sites. For the very first time, extensive investigations regarding their chemical and mineralogical composition as well as the influence of petrophysical properties on their weathering behavior were realized. Different groups of tuff rocks could be identified, which differ greatly in their chroma, texture, their chemical and mineralogical composition, as well as their weathering behavior. At 30% porosity and 25% micropores, the tuff rocks show a sharp limit of changing water transport and retention behavior. Swellable clay minerals, the amount of micropores and the hygroscopic sorption value show a direct relation with the hydric expansion and proved to be reliable parameters for its estimation. Zeolite minerals proved to drastically increase the sorption values of the tuff rocks and are discussed as a cause for potential disjoining pressure. Furthermore, the application of the salt bursting test by European standard on these glass-rich volcanic tuff rocks is questioned, due to considerable different mineralogy and fabric in comparison to classic ash-rich tuffs.