Please use this identifier to cite or link to this item: https://www.um.edu.mt/library/oar/handle/123456789/78598
Title: The treatment of weathered globigerina limestone : the surface conversion of calcium carbonate to calcium oxalate
Authors: Mifsud, Tabitha (2006)
Keywords: Limestone -- Malta
Building stones
Building materials
Issue Date: 2006
Citation: Mifsud, T. (2006). The treatment of weathered globigerina limestone : the surface conversion of calcium carbonate to calcium oxalate (Master's dissertation).
Abstract: This work concerns the investigation of ammonium oxalate treatment of weathered Globigerina Limestone of the "franka" (good quality stone) type. The other locally available limestone type, "soil" (bad quality stone) was not taken into consideration. To this end, "franka" limestone samples were subjected to a 5% ammonium oxalate poultice for 5 hours, after which testing took place on both treated and untreated samples. The range of samples included fresh quarry samples, artificially (salt) weathered quarry samples and naturally weathered samples. From each group of stones, both desalinated and non-desalinated sarnples were studied. The artificially weathered quarry samples were weathered using sodium sulphate for the samples that were to be later desalinated. Sodium chloride was used to artificially weather the non-desalinated samples as this is the predominant salt found in Globigerina Limestone in the local scenario. The first part of the investigations included X-Ray Deflection, where the formation of calcium oxalate following ammonium oxalate treatment was verified on the treated samples, as well as on exposed statuary that had been treated by others in 2003. The results obtained showed that whewellite was formed in all cases, whereas weddellite was never formed. It was also confirmed that the presence of sodium chloride does not hinder the formation of calcium oxalate in any way. In fact, non-desalinated samples were found to produce more calcium oxalate than desalinated samples of the same type. The effectiveness of the treatment was evaluated by means of Scanning Electron Microscopy (SEM) observations, Mohs hardness test, Tape test, acid resistance tests, depth of calcium oxalate formation investigations, sodium sulphate weathering tests, water absorption tests (by capillarity) and visual analyses. These studies showed that the production of calcium oxalate resulted in the formation of a more compact, more cohesive, and harder surface when compared to untreated samples. No colour differences were seen between treated and untreated samples, as verified by comparisons to Munsell Colour Charts. Also, the hydrophilic and wetting properties of the stone were retained in the treated samples. The formation of calcium oxalate in the treated samples was also found to have increased the stone's resistance to acid attack, and to salt weathering (using sodium sulphate). These promising results represent ammonium oxalate treatment of "franka" Globigerina Limestone in a positive light. In practical terms, it can in fact be concluded that this treatment can potentially be used in the field of conservation as a protective treatment, possibly with some consolidating properties, on historic buildings and monuments In the Maltese Islands, although further investigations are required.
Description: M.SC.CONSERVATION
URI: https://www.um.edu.mt/library/oar/handle/123456789/78598
Appears in Collections:Dissertations - FacBen - 1970-2018
Dissertations - FacBenCBH - 1997-2017

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