WEATHERING OF SEDIMENTARY STONE MATERIALS FORMED UNDER EARTH SURFACE CONDITIONS

Quaternary calcareous sediments, such as breccias and tufa play an important role as historic building materials – their use dates back far into historical times. These materials, although mostly of local occurrence only, are frequently found in areas where the regional geology is characterized by calcareous rock series, e.g. in the Alpine and in the Balkan realms. Compared to limestone of geologically older pre-quaternary provenance these quaternary calcareous materials show mostly an excellent weathering resistance. Since stone deterioration in moderate climatic regions is closely related to water impact and hygric rock properties respectively, we analysed the relation of pore volume and the associated specific surface of quaternary sediments, lime mortars and prequaternary limestones. These properties are considered major petrophysical parameters in the decay processes. We compared data obtained on quaternary calcareous conglomerates, tufa-limestone and lime mortars as well as literature data of different limestones (Grimm 1990). We found a systematic correlation between the specific surface and its associated pore volume which are presented in diagrams of (spec. surface/pore vol.) versus pore volume. Surprisingly, the quaternary sediments and also mortars are characterized by the relatively largest quotient of specific surface to pore volume. This finding indicates that the weathering resistivity of these quaternary sediments is lastly not directly related to the pore properties in any case. Considering that the quaternary materials have been formed and remained on the Earth surface till quarrying, they are in a distinct contrast to limestones. These materials experienced after sedimentation a diagenetic adaptation to higher pressure-temperature condition in some depth of the Earth crust before they returned on the Earth surface in the course of geological processes. This difference suggests that thermodynamic constraints play an important role: while the normal limestones which have been conditioned in the depth, have to re-equilibrate to the conditions on the Earth surface, the quaternary sediments have been formed there and have never left this regime and are therefore in a fair equilibrium with the environment.