Muzahim Al-Mukhtar

The fabric of a clay soil under controlled mechanical and hydraulic stress states

Abstract Fabric determination is fundamental to the understanding of several mechanims controlling a clayey soil behavior. Two techniques; namely, mercury intrusion tests and transmission electron microscopy (TEM) were used to study the soil fabric of a remoulded Boom clay. The effect of overburden pressure, excavation and desaturation on the soil fabric are studied. Results demonstrate that the nature of soil fabric is dependent on both the applied mechanical and hydraulic stress state conditions.

Coupling analysis of macroscopic and microscopic behaviour in highly consolidated Na-laponite clays

Abstract The great importance of problems related to the storage of chemical and radioactive wastes requires better understanding of the behaviour of the host media. In the case of clay soils, their behaviour is controlled by their microtexture, their mineral composition and their physico-chemical properties (interaction between interstitial fluid and solid matrix). In this paper, the analysis of the behaviour of consolidated synthetic model clay Na-laponite is presented. Tests are conducted on samples submitted to axial stress for the determination of the distribution of pore space and the type of interstitial water. Analysis is based on data given by different techniques: BET, mercury intrusion, X-ray diffraction and thermogravimetric analysis. The basal spacing d 001 and the water content decrease respectively from 2.5 nm to 1.6 nm and from 140% to 63% when the axial mechanical stress increases from 1 to 10 MPa. Results obtained would allow to take into account the relationships between the applied stress on the samples and the basal spacing, the number of water layers and the water content in the formulation of numerical modelling of the macroscopic behaviour.

Application of digital techniques in monument preservation

Health records for monuments are produced to provide a basis for scientific monitoring and planning of restoration work. The collected data (locations of deterioration, and architectural and historical archives) must be referenced in a single documentation platform to establish a detailed diagnosis of the state of degradation of the monument. This paper presents the application of digital techniques for production of a health record of a monument, applied to the castle of Chambord (Loire Valley, France). The first step is to provide a 3D digital reconstruction of the monument. This 3D modelling consists in constructing a finely refined and relevant graphic base to spatially reference all data acquired during the project. Topography is used to precisely locate the relative position of the main architectural components, while photogrammetry can set in detail each of these elements. The application of textures extracted from pictures on surfaces of the 3D model provides a realistic appearance. Additional data from a laser scanner can be included to detail complex forms or specific degraded areas for monitoring or documentation purpose. The state of deterioration of the structure is evaluated through a visual in situ survey. Dating and identification of rocks are determined by searching in the historical and architectural archives that are sometimes incomplete. Finally, the NUBES web-based platform is used to spatially associate data with the 3D model of the monument. This database underpins the health record of the castle of Chambord.

Physical Characterization of Natural Straw Fibers as Aggregates for Construction Materials Applications

The aim of this paper is to find out new alternative materials that respond to sustainable development criteria. For this purpose, an original utilization of straw for the design of lightweight aggregate concretes is proposed. Four types of straw were used: three wheat straws and a barley straw. In the present study, the morphology and the porosity of the different straw aggregates was studied by SEM in order to understand their effects on the capillary structure and the hygroscopic behavior. The physical properties such as sorption-desorption isotherms, water absorption coefficient, pH, electrical conductivity and thermo-gravimetric analysis were also studied. As a result, it has been found that this new vegetable material has a very low bulk density, a high water absorption capacity and an excellent hydric regulator. The introduction of the straw in the water tends to make the environment more basic; this observation can slow carbonation of the binder matrix in the presence of the straw.

Evaluation of the compatibility of building limestones from salt crystallization experiments

Abstract Salt absorption in porous building stones contributes greatly to the degradation of monuments. Two French porous limestones with similar main characteristics (total porosity, densities and mechanical resistance) were studied: white Tuffeau and Sebastopol stone. Accelerated ageing (weathering) tests were carried out by applying immersion-drying cycles with water containing sodium sulphate or sodium chloride. Samples of the two stones were tested separately and then in sets containing both rock varieties. The results facilitated interpretation of the observed and measured responses of these two limestones to the cycling salt crystallization. The durability of studied stones was evaluated by determining the normalized weight changes during the applied cycles. The Sebastopol stone amplified the amount of salt stored in the Tuffeau with increasing number of cycles performed, inducing its more rapid degradation. Water retention and water transfer in the pore space were found to be two main factors controlling the rate and the type of stone decay due to the salt crystallization.

Historical Study of Chambord Castle: Basis for Establishing the Monument Health Record

The conservation of built heritage requires a good knowledge of the materials and the history of the monument in question. One objective of the SACRE Project (Suivi des Altérations, Conservation et Restauration des Monuments en Pierres Calcaires [Degradation Monitoring, Characterization and Restoration of Limestone Monuments]) is to establish the health record of a monument. Chambord Castle was built out of tuffeau limestone in 1519. This limestone, which comes from the Loire Valley, is extremely fragile, causing spalling and exfoliation to occur on the surface of the stone. The south facadethe entrance to the Castle—and the east tower are studied. The mapping of the different origins and dates of the stones forms the basis of the health record of the Castle. The comparison between this mapping and the location of damages on the facades shows different type and degree of degradation concerning tuffeau. The topography and the orientation of the building are also significant parameters that contribute to the development of specific types of degradation.

The occurrence of gypsum in the scaling of stones at the Castle of Chambord (France)

The main cause of degradation in tuffeau, a soft siliceous and clayey limestone extensively used in the construction of the castles of the Loire Valley in France, is scaling. The most damaging form of weathering is spalling. Over time, a plaque several centimetres in thickness gradually forms under the stone surface and eventually falls away, leaving the resulting new surface powdered. Hypotheses regarding the initiation and development of such degradation have not yet met scientific consensus. The objective of the present paper is to improve existing knowledge of scaling degradation by analysing in situ samples representing different stages of the same degradation process. The analysis of the stones at the Castle of Chambord, revealed the presence of gypsum (CaSO4·2H2O), mainly located in cracks parallel to the stone surface. This gypsum was then studied in terms of its crystal morphology and distribution with depth. For comparison purposes, another form of scaling identified at the Castle of Chambord but rarely studied, flaking, was also examined. A first attempt at explaining the origin and formation of the observed gypsum in both scaling processes was conducted by interacting and comparing the characterisation results with historical and environmental data.

Comparison between photomodelling and laser scanning to create a 3D model for a digital health record

This work deals with the creation of a digital health record for the Castle of Chambord (Loire Valley, France) to establish a detailed diagnosis of the state of deterioration of the monument. This digital health record aims to provide a basis for scientific monitoring and planning of restoration work by referencing data (mapping of deterioration and architectural and historical archives) on a Web-based documentation platform. The starting point is building a 3D model of the monument. This 3D model must meet specific requirements for its subsequent use, including the ability to be unfolded in 2D with visual consistency. The method to be used for 3D acquisition depends on a balance between speed of execution, cost, and compatibility with respect to data organisation. This paper presents a comparative study between photomodelling and laser scanning. The different steps needed to build a reliable 3D model with both techniques are demonstrated along with a critique of the advantages and disadvantages of each. Ce travail traite de la réalisation du carnet de santé numérique du château de Chambord (Vallée de la Loire, France) utilisé pour établir un diagnostic détaillé de l’état d’altération du monument. Ce carnet de santé numérique vise à proposer une base pour le suivi de l’ouvrage et la programmation de ses restaurations en référençant les données (cartographies d’altération, archives architecturales et historiques) dans une base de données web. Le point de départ consiste à construire un modèle 3D du monument. Ce modèle doit satisfaire aux contraintes spécifiques liées à son utilisation, notamment sa capacité à être déplié en 2D lisiblement. La méthode utilisée pour réaliser l’acquisition 3D repose sur un compromis entre rapidité d’exécution, coût, et compatibilité de format vis-à-vis de la base de données. Cet article présente une étude comparative entre la photomodélisation et le relevé par scanner laser. Les différentes étapes nécessaires à l’obtention d’un modèle 3D fiable sont décrites pour chaque technique, avec une critique des avantages et inconvénients de chacune.

Gypsum and spalling decay mechanism of tuffeau limestone

The general form of degradation of tuffeau is the progressive spalling of the surface of the stone. Over time, thick plates (1- to 3-cm thick) form gradually on the surface of the stone. Once the plate drops, the resulting stone surface turns into powder. At the Castle of Chambord, mineralogical analysis of the degraded stone, throughout its depth, shows the presence of gypsum (CaSO4·2H2O) located mainly within a crack network parallel to the surface. The objective of this research is to study different hypotheses of gypsum formation to improve the understanding of the damaging process of spalling. Fresh stones were subjected to artificial ageing in the laboratory through imbibition/drying tests, to study the resulting distribution of gypsum as a function of several parameters: the source of gypsum, initial stone cracking, drying conditions, and analysis after different measurement sequences. Tested samples were analysed at different stages of ageing by using X-ray diffraction and ion chromatography to localise and quantify the amount of gypsum throughout the depth. Results indicate that gaseous SO2 can lead to a distribution of gypsum very similar to that observed in stones subjected to spalling in situ at the Castle of Chambord.

Hydromechanical effects : (I) on the Na-smectite microtexture

Abstract Changes in particle organization and pore-spaces with applied mechanical and hydraulic stresses were followed using TEM, SAXS mercury porosimetry and gas adsorption for two Na-smectites, Laponite and hectorite, with similar structural formulae but different particle sizes. The TEM images show that hectorite has particles larger and more anisotropic than those of Laponite. The particles order perpendicularly to the direction of axial mechanical stress and become disoriented under hydraulic stress. According to the SAXS results, Laponite is composed of 1 3 small layers and hectorite of more compact (10 80 layers) particles. In Laponite, mechanical stress strongly reduces the amount of macropores but does not affect micropores and mesopores; hydraulic stress increases the macropores. In hectorite, the pore-volume is lower than in Laponite. The different techniques used yield complementary results and show the considerable effect of layer dimension on the behaviour and microtexture parameters of smectite submitted to hydromechanical stresses.