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Jeudi 27 Juin 2013

14 heures, bibliothèque du CRMD

Weathering crust and dust on limestone monuments : physical properties, chemical composition and environmental control

Dr Ákos Török, Department of Construction Materials and Engineering Geology – Université de Budapest

Résumé :

Limestone monuments located in urban, industrial and rural areas often show different weathering features. Weathering crusts, settling dust and host limestone samples were collected in Hungary and Germany at 13 sites. Micro-fabric (microscopy, SEM), mineralogical composition (XRD) and trace element distribution (LA-ICPMS) were analyzed to understand the contribution of dust to the formation of weathering crusts. Both weathering crusts and the dust found at urban sites are enriched in gypsum. In dust samples siliceous fly-ash particles are more common, than carbonaceous ones in both countries indicating the longer term stability of these particles. Mineral fragments in dust are abundant and their composition represents the geology of the background area. Gypsum crystal aggregates were also identified within dust samples indicating the rapid sulphation process. Lead mostly accumulates in dust, but also in the black crust, showing the highest lead concentrations close to the crust/limestone boundary. PAH was also recorded in dust and also in the limestone. The study suggests that both settling dust and black crust samples collected from limestone buildings could be used as environmental indicators of past and recent pollution levels.