Five volcanic tuffs ranging from dacitic tuffs of Hungary to rhyolite, phonolite and basaltic tuffs of Germany were consolidated under laboratory conditions. Prior to consolidation an anti-hygro, a hydrous consolidant, which reduces the swelling ability of clay minerals, was applied. The three consolidants, a silicic acid ester (SAE), an elastic silicic acid ester (eSAE) and an acrylate resin (PMMA) were applied on test specimens under vacuum. Petrographic characterisation (polarizing microscopy, XRD, SEM) provided data for fabric analyses and the mineral composition of the tuffs. Changes in fabric, effective porosity, density, tensile strength, ultrasonic wave velocity were evaluated after the treatment. Weathering simulation tests such as hygric dilatation and thermal dilatation aimed to prove the effectiveness of consolidation and the durability of consolidated tuff samples. More than 500 samples were analysed. The tests showed that SAE caused the highest increase in indirect tensile strength. The water absorption and the pore size distribution of the tuffs were modified by consolidation. The PMMA reduced the water absorption the most, whereas SAE modified it the least. All the tested consolidants increased the thermal dilatation of the tuffs. The changes in hygric dilatation were not uniform: for most tuffs SAE increased and PMMA decreased the hygric dilatation, although the clayrich Habichtswald tuff showed the opposite trend. The changes in hygric and thermal behaviour of consolidated tuff require special care when specific consolidants are chosen. These products modify the physical properties of consolidated tuffs and change the behaviour of weathering.

The construction suitability of a dimension stone depends on its weathering properties along with the petrology and the petrophysical properties. The aim of this study was to evaluate the suitability of the dimension stones from the ''Drei Gleichen'' area for construction and replacement purposes. In total, six sandstones (Ingersleben, Wachsenburg, Hindfelden, Seeberg, Röhnberg, Gleichenberg; Upper Triassic) as well as two carbonates (Wachsenburg sinter; Quaternary, Wandersleben dolomite; Middle Triassic) were analysed. The results from our laboratory and on-site studies of the dimension stones show that rocks from the same stratigraphic layer, like the sandstones from the upper Triassic, can show major differences in their petrophysical and weathering properties. These differences are attributed to their different diagenesis, resulting, e.g. in varying pore space, water balance and strength properties. The pore size distribution can be divided into four different groups based on their occurring maxima and micropore content. The determined water balance properties as well as moisture expansion and salt attack depend on these groups. Next to this, the mineralogical composition significantly influences the weathering resistance. Sandstones with a high content of altered lithoclasts show a high amount of moisture expansion, low strength and, in consequence, a low weathering resistance against salt attack. Based on the results of the present study, an evaluation of construction suitability could be accomplished. From the analysed sandstones, only the Seebergen sandstone is suitable for construction purposes due to its good availability, good strength properties (high compressive and tensile strength, low softening degree) as well as a low porosity. Furthermore, the Wachsenburg sandstone also shows good petrophysical and petrological properties, but exploitable deposits are too sparse to be of commercial interest. From the carbonates, the Wachsenburg sinter shows very suitable rock parameters, but only sparse outcrops occur, which are not appropriate for mining.

Most studies dealing with material properties of sandstones are based on a small data set. The present study utilizes petrographical and petrophysical data from 22 selected sandstones and *300 sandstones from the literature to estimate/predict the material and weathering behaviour of characteristic sandstones. Composition and fabric properties were determined from detailed thin section analyses. Statistical methods applied consist of data distributions with whisker plots and linear regression with confidence regions for the petrophysical and weathering properties. To identify similarities between individual sandstones and to define groups of specific sandstone types, principal component and cluster analyses were applied. The results confirm an interaction between the composition, depositional environment, stratigraphic association and diagenesis, which leads to a particular material behaviour of sandstones. Three different types of pore radii distributions are observed, whereby each is derived from different pore space modifications during diagenesis and is associated with specific sandstone types: (1) bimodal with a maximum in capillary and micropores, (2) unimodal unequal with a maximum in smaller capillary pores and (3) unimodal equable with a maximum in larger capillary pores. Each distribution shows specific dependencies to water absorption, salt loading and hygric dilatation. The strength-porosity relationship shows dependence on the content of unstable lithic fragments, grain contact and type of pore radii distribution, cementation and degree of alteration. Sandstones showing a maximum of capillary pores and micropores (bimodal) exhibit a distinct hygric dilatation and low salt resistance. These sandstones are highly immature sublitharenites-litharenites, characterized by altered unstable rock fragments, which show pointedelongated grain contacts, and some pseudomatrix. Quartz arenites and sublitharenites-litharenites which are strongly compacted and cemented, show unimodal unequal pore radii distributions, low porosity, high strength and a high salt resistance. The presence of swellable clay minerals in sublitharenites-litharenites leads to a medium to high hygric dilatation, whereas quartz arenites show little hygric dilatation. Sandstones with unimodal equal pore radii distribution mostly belong to weakly compacted and cemented mature quartz arenites. These are characterized by high water absorption and high porosity, low to medium strength and a low salt resistance. The data compiled in this study are used to create a sandstone quality catalogue. Since material properties are dependent on many different parameters of influence, the transition between different lithotypes is fluent.

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