Joerg Ruedrich

Thermal behaviour of weathered and consolidated marbles

Abstract To optimize stone consolidation it is necessary to understand the mechanisms of weathering in marbles, and its control by the mineralogical composition and the rock fabric. A knowledge of how the stone consolidants affect the weathering mechanisms and if they are compatible with the stone is also an important consideration. The weathering of marble can begin with thermal stress whereby cracks are generated. To verify whether consolidation influences the thermal behaviour of marbles, we compared the behaviour of weathered and consolidated marbles. For the investigations four marbles were selected with various fabrics (e.g. texture, grain size, grain boundary geometry, etc.) and different weathering conditions. Three consolidation approaches were adopted: a solved polymethyl-methacrylate (PMMAsol) dissolved in xylenes, a polysilicic acid ester (PSAE) and a total impregnation with a monomer methyl-methacrylate (PMMApoly). Measurements of the porosity and effective pore size distribution evidenced a strong modification of the pore space by consolidation. Both PMMA approaches show a re-establishment of cohesion which can be determined by ultrasonic velocity measurements. By reaching the respective glass transition temperatures of PMMAsol and PMMApoly, a strong modification of thermal behaviour occurs. The PSAE consolidated marbles show only minor changes of dilatation, but due to its low bonding effect no significant cohesion between the crystals occurs.

Length changes of sandstones caused by salt crystallization

Abstract Salt crystallization in the pore spaces of building stones can produce significant deterioration. The properties of the salt solution, the salt phases and the climatic conditions, as well as the rock fabric, significantly influence the state of rock weathering. To examine the influences of rock fabric and salt type on salt weathering, detailed investigations were performed on three sandstones. The fabric (mineralogical composition, grain size, etc.) and the petrophysical properties (porosity, pore-size distribution and hygric dilatation) of the sandstones were analysed and correlated with length changes during cyclic salt loading. The salt tests were carried out with two different salt types: (i) sodium sulphate and (ii) sodium chloride. The observed length changes differ for the investigated sandstones. Contractions of the samples, as well as a pronounced residual strain after the applied salt cycles, were observed. Specific deterioration features can be determined for the sandstones independent from the salt types used. However, the decay mechanisms, which lead to a significant deterioration, are different for sodium sulphate and sodium chloride. For sodium sulphate, a strong expansion occurs during the solution uptake cycles. This expansion can be attributed to hydration pressure during the transition from the water-free thenardite to the hydrate phase mirabilite. In contrast, the samples in the sodium chloride test show the main expansion in the drying stage. This can be related to the crystallization pressure caused by the growth of halite.

Limestones in Germany used as building stones: an overview

Abstract Germany has an enormous number of different carbonate rock units, which vary widely in their geological age and sedimentary depositional environment. Limestones quarried from these exposures have a wide range of usages and applications, such as dimension and ornamental stones, floor tiles and panelling, and for use as paving stones and massive stones. Since antiquity, limestones were used as building materials in areas where they were naturally available and abundant. Limestones exhibit a relatively good weathering resistance, which is mainly controlled by the mineralogical composition and the rock structure. The susceptibility of limestones to weathering and alteration is only secondarily related to the stones contact with rainwater and its exposure to frost. In this situation the pore space is the main controlling factor. Industrialization and the subsequent increase in air pollutants, which started at the end of the nineteenth century, led to the formation of dark and unsightly crust deposits on the limestones surfaces. These crusts, being the result of man-made activities, are the main weathering problem for carbonate dimension stones.