Porosity and mineralogy evolution during the decay process involved in the Chellah monument stones |
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Authors: | Abderrahim Samaouali Larbi Laânab Mohamed Boukalouch Yves Geraud |
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Institution: | 1.Laboratoire de Thermodynamique, Département de Physique, Faculté des Sciences,Mohammed V University,Rabat,Morocco;2.Centre de Microscopie, Département de Physique, Faculté des Sciences,Mohammed V University,Rabat,Morocco;3.Ecole et Observatoire des Sciences de la Terre, Institut de Physique du Globe Strasbourg UMR 7516,Université Louis Pasteur,Strasbourg Cedex,France |
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Abstract: | The objective of this work is to study the decay process involved in the historical Roman Chellah located in the Rabat city
(Morocco). This monument is made up of porous calcarenite stone. Several samples, taken from altered and unaltered blocks,
were analyzed by the water saturation, the mercury intrusion porosimetry techniques and using the scanning electron microscopy
coupled to energy dispersive X-ray spectrometer (SEM–EDX). To perform a reliable chemical analysis, some samples were also
analyzed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The mercury porosimetry results show a bimodal
porous network for this porous material, the deterioration process of these stones involved an increase in porous volume of
about 2%. The lowest porosity observed in the unaltered block is connected to the presence of sparitic cement which causes
a partial inter-granular porosity clogging. The highest porosity of the deteriorated block without crust is due to the increase
in inter-granular space. SEM photographs of the unaltered sample show the presence of the porous primary grains, of ovoid
forms and millimeter-length sizes, and of the secondary grains, of rhombohedric forms and micro size. Porosity is essentially
located between the primary grains and can be completely clogged by secondary precipitations. Various forms of deterioration
are observed on the altered samples such as the dissolution of the secondary grains edges, wells of dissolution and also the
presence of argillaceous residues on the surface. This last was also detected by the ICP-AES and EDX analysis which show an
increase of the silicon and aluminum contents toward the surface. |
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