Quality assessment of replacement stones for the Cologne Cathedral: mineralogical and petrophysical requirements

A critical factor in the deterioration of Cologne Cathedral's medieval 'Drachenfels trachyte' is its moisture properties, including capillary and sorptive water uptake, water saturation, drying processes, and moisture dilatation. This study assessed eight different stones used in the cathedral's construction, comparing their petrography, mineralogical composition, and petrophysical properties to those of Drachenfels trachyte. The research found significant differences in lithology and petrophysical characteristics among the stones, which are strongly correlated with their deterioration behavior. By defining optical and petrophysical criteria, including strength values, the study evaluated the compatibility of original, replacement, and modern building materials, highlighting that moisture properties play a pivotal role in the decay mechanisms observed.

Graue, B., Siegesmund, S., & Middendorf, B. (2011). Quality assessment of replacement stones for the Cologne Cathedral: mineralogical and petrophysical requirements. Environmental Earth Sciences, 63(7-8), 1799–1822. https://doi.org/10.1007/s12665-011-1077-x