Olivier Rozenbaum

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 stone.

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

Understanding 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.

Image processing for the non-destructive characterization of porous media. Application to limestones and trabecular bones

Different image processing techniques have recently been investigated for the characterization of complex porous media, such as bones, stones and soils. Among these techniques, 3D thinning algorithms are generally used to extract a one-voxel-thick skeleton from 3D porous objects while preserving the topological information. Models based on simplified skeletons have been shown to be efficient in retrieving morphological information from large scale disordered objects not only at a global level but also at a local level. In this paper, we present a series of 3D skeleton-based image processing techniques for evaluating the micro-architecture of large scale disordered porous media. The proposed skeleton method combines curve and surface thinning methods with the help of an enhanced shape classification algorithm. Results on two different porous objects demonstrate the ability of the proposed method to provide significant topological and morphological information.

Degradation mechanisms of reinforcing iron rebars in monuments: the role of multiscale porosity in the formation of corrosion products investigated by X-ray tomography

Monuments in stone often contain metallic reinforcements, the stability and degradation state of which determines the entire integrity of the edifice. Understanding their long-term corrosion process is thus an essential step towards a safe and efficient conservation strategy. In this study, we show that combining laboratory and synchrotron tomography at different scales is efficient for getting an overall three-dimensional picture of the iron corrosion products found in iron rebars from Orleans cathedral. We demonstrate that beside chemical characterization of the corrosion products, the study of the shape of the corrosion products, their spatial distribution within the stone binder and their relationship with the porosity of the binder can bring significant insights into the corrosion process, and particularly help in understanding the multiple roles that porosity plays in corrosion.

Optical indices and transport scattering coefficient of pyrolytic boron nitride: a natural thermal barrier coating for solar shields

Absorption and scattering properties of pyrolytic boron nitride (pBN) have been characterized by infrared spectroscopy. The strong dielectric anisotropy predicted by first principles calculations is confirmed by measurements performed on a highly oriented pBN sample. Optical properties of textured samples elaborated by chemical vapor deposition were identified from normal hemispherical reflectance and transmittance spectra by applying modified two-flux and four-flux transport models. It is also shown that coating carbon–carbon composites used to build solar shields with a pBN layer having an optimal thickness could improve the protection performance.

3D Reconstruction of the proximal femur shape from few pairs of x-ray radiographs

This paper presents a 3D reconstruction method of the proximal femur shape based on contour identification from pairs of 2D X-ray radiographs. The aim is to reconstruct the 3D surface of the proximal femur from a limited number of projections. Our approach is based on the reconstruction of several 3D contours, which are meshed to obtain a 3D shape. Our proposed algorithm is based on different processing steps to obtain the 3D personalized model. Three approaches are proposed. The first technique consists of contour extraction, matching the points of these contours and calculation of a 3D contour using an original algorithm. The second and third techniques use the results of the previous method as well as new points chosen by an operator from a reference model of femur to improve accuracy either globally or only in sensitive areas. The proposed method was evaluated on 10 cadaveric proximal femurs using the 3D CT-Scan models. Obtained results show good performance and promising perspectives for 3D shape reconstruction of the femur from only a few pairs of radiographs.

Mechanical Assessment of Trabecular Bone Stiffness using Hybrid Skeleton and Finite Element Analysis

The form primitives of trabecular bone can be modelled as a complex structure of rods and plates. The classification of these primitives helps in simulating the physical or mechanical properties which are usually determined not only by the porosity of the object, but also by the arrangement of structure primitives in the 3D space. Based on the classified trabecular bone primitives, we propose in this work a finite element model that is both simple and fast while preserving the accuracy of the analysis. Rods are modelled as beams with circular cross sections. For the plate-like primitives, a triangulation method is used to characterise the behaviour of the corresponding shell elements. Using the proposed method, multiple features can be generated and combined in a statistical discriminant analysis in order to study the mechanical behaviour of selected trabecular bone samples. A clinical study was conducted on two populations of arthritic and osteoporotic bone samples. The results show the ability of our beam/shell model to discriminate the two populations.