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Fassier M.,CNRS Heterogeneous Materials Study Group | Fassier M.,Center Technique Of Materiaux Naturels Of Construction | Peyratout C.S.,CNRS Heterogeneous Materials Study Group | Smith D.S.,CNRS Heterogeneous Materials Study Group | And 2 more authors.
Journal of the European Ceramic Society | Year: 2010

Heterogeneous photocatalysis can be exploited for the decomposition of micro-organisms which have developed on the surfaces of building materials. In this work, the efficiency of titanium dioxide coatings on fired clay products is examined. The sol-gel method is used to synthesize a fine TiO 2 powder with a specific surface area of 180m 2g -1. Thermal treatment of the chemical gel at 340°C leads to crystallisation in the anatase phase and with further temperature increase, crystallite growth. For thermal treatments in the range 580-800°C, there is a progressive transition from anatase to rutile. However, despite a decrease in specific surface area of the powder attributed to aggregation/agglomeration, the coherent domain size deduced from X-ray diffraction measurements remains almost constant at 23nm. Once the transition is completed, increase of thermal treatment temperature above 800°C leads to further crystallite growth in the rutile phase. The thermally treated titania powders were then sprayed onto fired clay substrates and the photocatalytic activity was assessed by the aptitude of the coating to degrade methylene blue when exposed to ultraviolet light. These tests revealed that the crystallite size is the important controlling factor for photocatalytic activity rather than the powder specific surface area or the anatase/rutile polymorph ratio. © 2010 Elsevier Ltd.

Malfilatre C.,CNRS Geosciences Laboratory of Rennes | Malfilatre C.,Center Technique Of Materiaux Naturels Of Construction | Hallot E.,CNRS Geosciences Laboratory of Rennes | Boulvais P.,CNRS Geosciences Laboratory of Rennes | And 6 more authors.
Bulletin de la Societe Geologique de France | Year: 2014

Two examples of granitic stones from Brittany (western France) commercialized under the names of "gris-bleu de Louvigné" and "bleu de Lanhélin" were characterized in order to explore how the provenance of a building stone can be traced back with a maximum of confidence. For this purpose, petrographical, geochemical and magnetic characteristics, representing more than 70 quantitative and qualitative variables, were compiled for a total of 32 samples. We have defined two reference populations for these building stones and have extracted their discriminative characteristics. We have then compared four randomly selected samples and two foreign commercial counterparts of these stones to the reference populations. Discriminative variables differ from one case of comparison to the other, which indicates that a combination of various tools and variables will be generally required to unequivocally fingerprint the origin of a given granitic stone. Where several quarries are mining a single geological unit within a composite intrusion, the provenance of a granitic rock can be defined at the scale of the intrusion. In addition, stones coming from two different intrusions from the same batholith can be distinguished. We conclude that the provenance of any granitic building stone is identifiable, especially if the intrinsic variability of a population of samples representative of that stone has been previously circumscribed. This study underlines that the compilation of databases for building stone identity cards is an essential first step toward the creation of official labels guaranteeing stone provenances.

Perrin B.,CNRS Materials and Construction Durability Laboratory | Vu N.A.,CNRS Materials and Construction Durability Laboratory | Multon S.,CNRS Materials and Construction Durability Laboratory | Voland T.,Center Technique Of Materiaux Naturels Of Construction | Ducroquetz C.,Center Technique Of Materiaux Naturels Of Construction
Construction and Building Materials | Year: 2011

The aim of this paper is to study the frost durability of fired clay materials. The behaviour of five fired clay materials with different physical and mechanical properties (porosity, permeability, mechanical strengths and elasticity modulus) subjected to freeze-thaw cycles is analysed. The strains of specimens and the evolution of the main properties with the number of cycles are assessed. The analysis shows that the pore distribution is not the only important parameter but that the tensile strength is also significant. A complete data bank is thus built up to study the effects of the physical and mechanical parameters on frost resistance and to determine how these parameters are affected by frost cycles. It will be possible to use these data to improve the modelling of coupled thermo-hydro-mechanical phenomena involved during the freezing and thawing process in porous media. © 2010 Elsevier Ltd. All rights reserved.

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