Artificial weathering of Spanish granites subjected to salt crystallization tests: Surface roughness quantification |
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| Institution: | 1. Grupo de Petrología aplicada a la Conservación del Patrimonio, Instituto de Geología Económica (CSIC-UCM), José Antonio Nováis 2, 28040, Madrid, Spain;2. Laboratorio de Piedra Natural, Instituto Geológico y Minero de España (IGME), Calera 1, 28760 Tres Cantos, Madrid, Spain;3. Departamento de Petrología y Geoquímica, Facultad de Geología, Universidad Complutense de Madrid (UCM), Jose Antonio Nováis 2, 28040, Madrid, Spain;1. Department of Chemistry, School of Science, Xi’an Jiaotong University, 710049 Xi’an, China;2. Institute for the preservation of cultural heritage, Yale University, 27395 West Haven, CT, USA;1. MTAIC Ltd (MTA International Company), Floor Khartoum, Sudan;2. Geological Engineering Department, Ankara University, Ankara, Turkey;3. Mining Engineering Department, Niğde Omer Halisdemir University, Niğde, Turkey;4. Geological Engineering Department, Konya Technical University, Konya, Turkey;5. Civil Engineering Department, Batman University, Batman, Turkey;1. Dipartimento di Ingegneria Civile, Ambientale e Architettura, via Marengo 2, 09123 Cagliari, Italy;2. Consiglio Nazionale delle Ricerche (CNR), Istituto di Scienze dell’Atmosfera e del Clima (ISAC), Via Piero Gobetti, 101 Bologna, Italy;3. Instituto de Geociencias IGEO (CSIC, UCM), Spanish Research Council CSIC – Complutense University of Madrid UCM, Madrid, Spain;4. Facultad de Ciencias Geológicas, Complutense University of Madrid (UCM), Madrid, Spain |
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| Abstract: | For hundreds of years, two types of granite (Zarzalejo and Alpedrete) from the Madrid region, Spain, have been extensively used as building stones. Fresh specimens of both stone types have been sampled from their respective quarries and subjected to sodium sulphate salt crystallization test (SCT). The resulting physical and chemical weathering patterns have been characterized by polarized light optical and environmental scanning electron microscopy. Water absorption under vacuum conditions and mercury intrusion porosimetry techniques were used to determine the pre- and post-SCT porosity and pore size distribution. The following non-destructive techniques were performed to assess stone durability and decay: ultrasound velocity (US) and surface roughness determination (SR) of intra- and inter-granular quartz, feldspar and biotite minerals at the centre as well as at the corners and edges of specimen surfaces. Before the SCT, US values were lower and SR values higher in Zarzalejo (ZAR) than Alpedrete (ALP) granite. After SCT, the US values declined while SR rose in both types of granites, with greater average differences in ZAR than ALP for both parameters. Feldspar and biotite and their inter-granular contacts were found to be the weakest and therefore the most decay-prone areas of the stone.The initial SR parameters were generally higher and rose more steeply after SCT at the corners and around the edges of the specimens.While behaviour was found to be similar in the two types of granite, variations were greater in ZAR, the less durable and more decay-prone of the two. Surface roughness measurement of mineral grains in granite stones is a very useful, in situ, non-destructive technique for quantifying salt crystallization-mediated physical and chemical weathering. The resulting quantification of decay and of related durability provides insight into the future behaviour of this type of stone, commonly used in historic buildings. |
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