Cit:AbuAlhassan:2018: Difference between revisions

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== Abstract  ==
== Abstract  ==
This paper reports on our preliminary attempt to perform dynamic laboratory measurements of salt crystallization and subsequent deliquescence on a surface of a porous material specimen (autoclaved aerated concrete as a model material) by using a high-resolution digital optical microscope that allows generating three-dimensional images. A specimen that is initially filled with a NaCl solution is dried in a room at ~26°C and ~40% RH for 14 days and is then wetted in a desiccator at ~95% RH during the next 14 days. A temporal change of the spatial distribution of the volume occupied by salt crystals on the specimen surface is determined based on the contrast between two microscopic images successively taken with a certain interval of time. The mass of the specimen is also measured simultaneously to determine the rate of water evaporation/absorption. The results show that salt crystallization during drying is not spatially uniform throughout the specimen surface, which likely depends on the spatial distribution of the pore structure in the specimen, and salt crystal deliquesces faster near the edges of the specimen than in the centre, which indicates a stronger dependency of salt deliquescence on the geometry of the specimen than on the inner pore structure of the specimen.
Salt weathering is considered one of the most decisive factors for damage on the rock-cut monuments in Petra / Jordan. The monuments are contaminated with salt by rain, water runoff and capillaries which results in complex mixtures of different salts causing damage to the stone. The risk our cultural heritage currently faces from salts might lead to its irretrievable loss. Although the problem is prevalent worldwide, appropriate conservation methods and techniques have not yet been fully explored. Entire removal of salts will not be possible in the case of the Petra monuments. However, partial removal of salts might at least slow down the destruction process currently threatening the rock-cut monuments of Petra. Even so, the traditional techniques of desalination, so far mainly with respect to the use of poultices have not yet achieved considerable success. New approaches are needed for improved desalination efforts and/or mitigation of salt weathering processes. A quite new field of research is the use of salt crystallization inhibitors/modifiers. It has attracted interest for the improvement of desalination as well as for reducing aggressiveness and damage potential of salt weathering regimes. In this context, previous research has shown that the use of sodium ferrocyanide might turn out as a promising treatment measure for removal of salt, as it has the ability to transport salt to the surface and thus promote the formation of efflorescences instead of subflorescences. To date, however, fundamental knowledge with respect to the interaction of such additives with salts in stone monuments and its implications on stone deterioration processes is still lacking. This study aims to evaluate the efficacy of (Sodium ferrocyanide decahydrate (Na4Fe(CN)6.10H2O) with respect to removability of salt from stone. Different sandstones from Petra were chosen for this study. The methodological approaches comprise basic petrographical - petrophysical investigations, 1st treatment with salts, 2nd treatment with crystallization inhibitors (different concentrations) and evaluation with respect to removability of salts. The results showed that the presence of inhibitor modifies the drying time of salt solutions inside the samples and makes the drying process faster than the drying of samples salinated with salts only. This allows the migration of a salt solution from the samples up to their surface, which results in the formation of non-destructive efflorescences rather than destructive subflorescences. The success of the treatment by the crystallization inhibitor is controlled with the formation of efflorescences, which was higher in the case of samples containing a mixture of salts than the samples salinated with pure single salt only.


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Latest revision as of 17:23, 22 November 2018

Author Abu Alhassan, Yazan
Year 2018
Title The use of sodium ferrocyanide for the removal of salt from stone, exemplified for sandstones from Petra - Jordan
Bibtex @phdthesis {AbuAlhassan:2018,

title = {The use of sodium ferrocyanide for the removal of salt from stone, exemplified for sandstones from Petra - Jordan}, school = {RWTH Aachen University}, year = {2018}, type = {Dissertation}, address = {Aachen}, note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen University; Dissertation, RWTH Aachen University, 2018}, url = {http://publications.rwth-aachen.de/record/729451 }, doi = {10.18154/RWTH-2018-226422}, author = {Abu Alhassan, Yazan} }

DOI 10.18154/RWTH-2018-226422
Link File:Phdthesis AbuAlhassan 2018 UniAachen-729451.pdf
Notes Dissertation, RWTH Aachen University, 2018, Veröffentlicht auf dem Publikationsserver der RWTH Aachen University



Bibliography[edit]

[Abuku.etal:2017]Abuku, Masaru; Ogura, D.; Hokoi, S. (2017): A preliminary study on dynamic measurement of salt crystallization and deliquescence on a porous material surface using optical microscope. In: Laue, Steffen (eds.): Proceedings of SWBSS 2017. Fourth International Conference on Salt Weathering of Buildings and Stone Sculptures, University of Applied Sciences Potsdam, Germany, 20-22 September 2017,Verlag der Fachhochschule Potsdam 42-48, 10.5165/hawk-hhg/319.Link to Google ScholarFulltext link

Abstract[edit]

Salt weathering is considered one of the most decisive factors for damage on the rock-cut monuments in Petra / Jordan. The monuments are contaminated with salt by rain, water runoff and capillaries which results in complex mixtures of different salts causing damage to the stone. The risk our cultural heritage currently faces from salts might lead to its irretrievable loss. Although the problem is prevalent worldwide, appropriate conservation methods and techniques have not yet been fully explored. Entire removal of salts will not be possible in the case of the Petra monuments. However, partial removal of salts might at least slow down the destruction process currently threatening the rock-cut monuments of Petra. Even so, the traditional techniques of desalination, so far mainly with respect to the use of poultices have not yet achieved considerable success. New approaches are needed for improved desalination efforts and/or mitigation of salt weathering processes. A quite new field of research is the use of salt crystallization inhibitors/modifiers. It has attracted interest for the improvement of desalination as well as for reducing aggressiveness and damage potential of salt weathering regimes. In this context, previous research has shown that the use of sodium ferrocyanide might turn out as a promising treatment measure for removal of salt, as it has the ability to transport salt to the surface and thus promote the formation of efflorescences instead of subflorescences. To date, however, fundamental knowledge with respect to the interaction of such additives with salts in stone monuments and its implications on stone deterioration processes is still lacking. This study aims to evaluate the efficacy of (Sodium ferrocyanide decahydrate (Na4Fe(CN)6.10H2O) with respect to removability of salt from stone. Different sandstones from Petra were chosen for this study. The methodological approaches comprise basic petrographical - petrophysical investigations, 1st treatment with salts, 2nd treatment with crystallization inhibitors (different concentrations) and evaluation with respect to removability of salts. The results showed that the presence of inhibitor modifies the drying time of salt solutions inside the samples and makes the drying process faster than the drying of samples salinated with salts only. This allows the migration of a salt solution from the samples up to their surface, which results in the formation of non-destructive efflorescences rather than destructive subflorescences. The success of the treatment by the crystallization inhibitor is controlled with the formation of efflorescences, which was higher in the case of samples containing a mixture of salts than the samples salinated with pure single salt only.