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Alveolar weathering of Cretaceous building sandstones on monuments in Saxony, Germany

By
Heiner Siedel
Heiner Siedel
Dresden University of Technology
,
Institute of Geotechnical Engineering, Chair of Applied Geology, D-01062 Dresden
,
Germany
(e-mail: Heiner.Siedel@tu-dresden.de)
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Published:
January 01, 2010

Abstract

The pattern of alveolar weathering on Cretaceous building sandstones from Saxony has been studied and related to the sandstone rock fabric and the spatial distribution of soluble salts at two monuments. The results demonstrate that uneven weathering of the stone surface is initiated by differences in porosity and mineral composition at macroscopic or microscopic scale within the heterogeneous material. Magnesium sulphate, the dominant salt, accumulates in areas with a higher content of clay minerals or ferric oxides/hydroxides, characterized by a higher amount of smaller pores. At an incipient stage, small pits in the surface are formed by salt weathering at these points. The stone dries more slowly from the base of these pits, thus accumulating more salt and leading to further material loss. Once deepened, the hole can shelter efflorescing salts from rain. The preferential weathering at the surface of the holes by salt crystallization and hydration pressure becomes a self-perpetuating process at this second stage, dependent only on changing moisture and climate. Building materials (mortars) and sulphur derived from air pollution are the main sources of the salts involved in the process of alveolar weathering on the investigated buildings. In contrast, salts that cause alveolar weathering of the Cretaceous sandstone bedrock in natural outcrops in Saxony mainly originate from long-term chemical weathering of the rock itself.

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Contents

Geological Society, London, Special Publications

Natural Stone Resources for Historical Monuments

R Přikryl
R Přikryl
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Á Török
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Geological Society of London
Volume
333
ISBN electronic:
9781862395817
Publication date:
January 01, 2010

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