Mechanizm rozpadu piaskowców wywołany krystalizacją soli
Abstract
Geneza krzemieni i czertów należy do największych zagadek współczesnej geologii. Od 1999 r. zespół polsko-amerykański, reprezentowany przez autorów niniejszego artykułu, prowadzi badania nad wyjaśnieniem warunków tworzenia się krzemieni górnojurajskich w rejonie Ożarowa (NE obrzeżenie Gór Świętokrzyskich). Stwierdzono istnienie antykorelacji pomiędzy *D i *18O. Obecne badania koncentrują się nad dwoma najbardziej prawdopodobnymi modelami genetycznymi krzemieni: (1) zmian temperatur na skutek działalności podmorskich źródeł hydrotermalnych, (2) samoorganizującej się katalitycznej krystalizacji. Uzyskane wyniki będą stanowić istotny wkład do badań nad genezą krzemieni i czertów z różnowiekowych formacji skalnych.
THE MECHANISM OF SANDSTONE DETERIORATION CAUSED BY SALT CRYSTALLIZATION
Summary
Tests of sulphate and nitrate crystallisation in Triassic and Jurassic sandstones from outcrops of the SE margin of the Holy Cross Mts were performed to determine the deterioration effect of salts on these rocks. The sandstones from this area have been used for centuries as a building stone material in the Warsaw architecture. As a reference sample a piece of the sandstone from the LOT building was used. During the last forty years this sandstone has been affected by atmospheric pollution derived from downtown. In sandstone samples from outcrops, as well as in a reference sample, fabric (composition, microstructures, habit of phases), porosity and durability were examined — before and after the tests. As a result of sulphate crystallisation, the anisotropy of the structure distinctly increases, wheras the porosity and the durability decreases. The weakening of the rock fabric is visible. No leaching of matrix components or quartz grains is noticeable. The nitrate crystallisation reduces the porosity of the sandstone even to a greater extent; the fabric of a sample is still preserved. Although the reference sample shows traces of washing-out of sandstone components and a small increase of permeability, the most important change is a fabric destruction in the rock. The prevailing deterioration mechanism of sandstone destruction in Warsaw monuments seems to be linked to bursting salt crystallisation. The strain caused by the salt crystallisation prevails over the leaching of rock s components which is a process of lesse importance.
THE MECHANISM OF SANDSTONE DETERIORATION CAUSED BY SALT CRYSTALLIZATION
Summary
Tests of sulphate and nitrate crystallisation in Triassic and Jurassic sandstones from outcrops of the SE margin of the Holy Cross Mts were performed to determine the deterioration effect of salts on these rocks. The sandstones from this area have been used for centuries as a building stone material in the Warsaw architecture. As a reference sample a piece of the sandstone from the LOT building was used. During the last forty years this sandstone has been affected by atmospheric pollution derived from downtown. In sandstone samples from outcrops, as well as in a reference sample, fabric (composition, microstructures, habit of phases), porosity and durability were examined — before and after the tests. As a result of sulphate crystallisation, the anisotropy of the structure distinctly increases, wheras the porosity and the durability decreases. The weakening of the rock fabric is visible. No leaching of matrix components or quartz grains is noticeable. The nitrate crystallisation reduces the porosity of the sandstone even to a greater extent; the fabric of a sample is still preserved. Although the reference sample shows traces of washing-out of sandstone components and a small increase of permeability, the most important change is a fabric destruction in the rock. The prevailing deterioration mechanism of sandstone destruction in Warsaw monuments seems to be linked to bursting salt crystallisation. The strain caused by the salt crystallisation prevails over the leaching of rock s components which is a process of lesse importance.