Examination of Deterioration Problems of Andesite Used in Aigai Agora

Abstract

The archaeological sites should be conserved as being the documents of ancient civilizations as a part of the built cultural heritage. In this study, the deterioration problems of stone used in the construction of the agora building in the archaeological site of Aigai (Manisa/Turkey) was investigated for the aim of its conservation. For this purpose, the building was documented by photographs and drawings. The stone deteriorations were documented on the drawings and samples were collected from the deteriorated and sound parts of stones. Basic physical properties, mineralogical, chemical and microstructural characteristics of the stone samples were determined to define the causes of deteriorations. X-Ray diffraction, scanning electron microscope, polarized microscope, infrared spectroscopy and thermogravimetric analyzer were used in the analysis. The stone used in the building is andesite which is mainly composed of andesine, albite high, anorthite, kyanite, labradorite, muscovite, microline, mullite, orthoclase, orthoferrosilite, quartz, sanidine and tridymite minerals. The density and porosity values of sound andesite are 2.4 g/cm3 and 8 % by volume respectively. On the weathered parts of the stone, the porosity increases with degree of weathering. The depth of the weathered zone from the surface to the inner parts which was determined by SEM analysis is about 1.7 cm. On the weathered parts of stone, clay minerals and iron oxides were determined as weathering products of andesite. The existence of clays on the exterior and the interior parts of the andesite accelerates weathering by their swelling.shrinkage properties and provide suitable conditions for the biological growth. Main weathering forms observed on the stone surfaces are detachment, deposits and loss of stone materials. The progress of weathering forms depends mainly on the difference in temperature and humidity between night and day at the site. Condensation and frost occurs mostly in winter months with increasing relative humidity and decreasing temperature. Humid and rainy conditions of winter months promote the weathering of the stone.