3-D characterization of weathered building limestones by high resolution synchrotron X-ray microtomography

International audienceUnderstanding the weathering processes of building stones and more generally of their transfer properties requires detailed knowledge of the porosity characteristics. This study aims at analyzing three-dimensional images obtained by X-ray microtomography of building stones. In order to validate these new results a weathered limestone previously characterised (Rozenbaum et al., 2007) by two-dimensional image analysis was selected. The 3-D images were analysed by a set of mathematical tools that enable the description of the pore and solid phase distribution. Results show that 3-D image analysis is a powerful technique to characterise the morphological, structural and topological differences due to weathering. The paper also discusses criteria for mathematically determining whether a stone is weathered or not

Modification and modeling of water ingress in limestone after application of a biocalcification treatment

International audienceWater transfers have been recognized as the main vectors of alteration and are responsible for pore network modifications in building stone. Among the techniques used to limit or stop the penetration of water into the stone, the calcification properties of bacteria have been investigated and used to treat buildings. In this article we study the effect of such a treatment following a protocol used in situ. The effects of this biotreatment on limestone (here tuffeau) were measured over a large number of drying-imbibition cycles. As the imbibition curves did not follow the usual Washburn law, a model based on a space-dependent permeability coefficient is proposed. It leads to a non-linear diffusion model which accounts for the deviation from the standard Washburn model

Pierres des Monuments Historiques : Caractérisations et mécanismes d'altération du Tuffeau.

Les matériaux poreux de construction tels que les pierres en oeuvre captent l'humidité suivant les conditions environnementales (température, humidité relative de l'air, eau de pluie, remontées capillaires provenant du sol). Ainsi, les flux d'eau à travers la pierre affectent de manière importante son comportement et sont principalement responsables des altérations rencontrées. Le tuffeau est une roche calcaire sédimentaire blanchâtre, tendre et poreuse, abondante dans le val de Loire. Le nom "tuffeau" vient du latin tofus signifiant pierre spongieuse. L'étymologie indique clairement la caractéristique principale de ce matériau : sa forte perméabilité liée à sa forte porosité. Cette pierre, qui se travaille facilement, est la pierre principale de construction des châteaux de la Loire, ainsi que de la plupart des anciennes maisons de cette région. De nos jours, le tuffeau est principalement utilisé pour la restauration des monuments anciens

Texture and Porosity Effects on the Thermal Radiative Behavior of Alumina Ceramics

International audienceThermal and optical properties of ceramics are dependent on radiation scattering and cannot be determined by a knowledge of their chemical composition alone, as for single crystals. In this paper, extrinsic effects, such as roughness, porosity, and texture, on the spectral emissivity of alumina ceramics are investigated. Roughness effects have an influence mainly in the opaque zone; an important porosity dependence and the presence of a critical porosity threshold were observed in the semitransparent zone. Furthermore, it was shown that two ceramics with similar total porosities, but with different textures, possess radically different emissivities, showing that grain size, pore size, and spatial repartition of the grains are also crucial for an understanding of the thermal properties of the ceramics

Significance of a combined approach for replacement stones in the heritage buildings' conservation frame

Stone substitution is a conventional operation during heritage buildings' restoration, but becomes problematic for architects and restorers when the quarry is mined out. The compatibility of the substitution stones with the original ones has been for long mainly based on the aesthetical aspect, this resulting too often in a patchwork of original and substitution stones with different patina after several years because of differences of properties. In this study, the objective is to show how substitution stones can be selected by combining aesthetic criteria and stones properties that are relevant for analyzing their compatibility. A couple of French limestones with their potential substitution stones were selected for the study. Our results showed that potential substitution stones selected on their aesthetic criteria require to be rejected because of their differences of physical properties. On the other hand, our results showed also the possibility to select substitution stones with satisfactory aesthetic aspect and properties that enable to expect a satisfactory compatibility with the original stone

Textural characterization using P. Gy heterogeneity functions.

International audienceA solid can be regarded as a set of contiguous elementary units. The distribution within the solid of any properties, measurable within each elementary unit, can be characterized using two parameters. These parameters are built using the constitution and distribution heterogeneities of P. Gy (1982, 1988). The former account for the granularity of the elementary units, whereas the latter assess the spatial distribution of the property. A texture which definition involves several properties can be described using a diagram where both parameters work as variables. Potential applications encompass: (i) the textural classification of soils, ore, breccia and concrete and (ii) the monitoring of textural transformation during process like dolomitization, metamorphism, weathering, deformation or annealing

Characterization, water transfer properties and deterioration in tuffeau : building material in the Loire valley-France

Water plays a fundamental role in the phenomena of stone deterioration. A highly porous limestone called tuffeau used in the Loire castles in France is characterized. Several techniques for pore space investigation and anisotropy determination are presented and their range of application is discussed. Water retention and transfer properties related to the pore space characteristics are determined as a function of relative humidity. The experimental set-up and tests presented have been chosen for their simple execution and interesting data produced for both fresh and deteriorated ston

Evidence of a bacterial carbonate coating on plaster samples subjected to the Calcite Bioconcept biomineralization technique

International audienceDegradation of historical buildings is mainly due to the intrusion of water which is the main vector of pollutants. Different types of surface treatment have been proposed to avoid or limit this effect. One alternative to chemical treatments is the use of the carbonatogenesis property of some bacteria. This bacterial production has been evidenced on concrete and on limestone samples in an aqueous environment. However, the carbonate production was measured indirectly and the experimental protocol was far from real conditions of use. In this paper, with the same protocol as an industrial one, and using a surface selective investigation method, grazing incidence X-ray diffraction, we show the structural and morphological evolution of the carbonate coating produced on model plaster samples. This substrate was chosen in order to unambiguously detect the bacterial carbonate production

Multi-scale characterization of monument limestones.

Among the parameters influencing stone deterioration, moisture and water movements through the pore network are essential. This communication presents differents methods to characterize stones and to determinate the water transfer properties. Results are analysed for two limestones having similar total porosity, but characterized by different pore networks. These different porous systems govern dissimilar water properties