Xavier Brunetaud

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.

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.

On the use of eggshell lime and tuffeau powder to formulate an appropriate mortar for restoration purposes

Abstract Preservation of cultural heritage, especially historic monuments, is a vital task. In addition, waste recovery is an essential goal of sustainable development. In this study the properties of a food waste, eggshells, and a quarry waste, powder obtained from stone-extraction operations, are evaluated in terms of their possible use in restoration mortar. An excellent lime has been developed based on eggshell calcination. A lime-based mortar exclusively composed of this eggshell lime and tuffeau powder was developed and characterized in order to demonstrate its compatibility with restoration works. To pursue this objective, microstructural, physical and mechanical properties were investigated and compared to those of the tuffeau limestone. The tested formulation using tuffeau powder was found to meet compatibility requirements up until the hygrometric environment lowered the water content of the mortar. The desiccation of the mortar can then generate shrinkage cracks leading to mortar crumbling. As a consequence, hygrometric susceptibility of the mortar is an essential parameter to be investigated in order to study the durability of lime-based mortars made out of limestone powder.

Documentation and Analysis of 3D Mappings for Monument Diagnosys

The restoration and preservation of built cultural heritage requires a good knowledge of its history and its current state of conservation. Heritage con-servation professionals are used to perform mappings to record and disseminate data relative to the monument. Data to be collected are heterogeneous, starting from the oldest sources (such as archives or iconographic manuscript) up to field observations. This study is applied to the documentation and analysis of the state of conservation of the East tower in the castle of Chambord. The produced map-pings concern the dating of stonework, the nature and origin of each stone, and the distribution of degradation patterns on the outer walls. To enable the graphical drawing and viewing of the different mappings, it is necessary to produce a suitable digital medium. In this study, the medium is a textured 3D model as a mean to characterize accurately and actually all surfaces, including those that cannot be viewed on a 2D projection. This 3D model is associated to the NUBES database to store and analyse all collected data. NUBES is a web-based open source platform for the representation, documentation and analysis of architectural elements. This information system has been specifically developed to include an interface dedicated to the drawing vector mappings and to their organization into hierarchical layers. Results of this study can be used to improve the monument diagnosis and our knowledge of weathering processes.

3D information system for the digital documentation and the monitoring of stone alteration

Today mapping of alterations of cultural heritage buildings and estimation of their degradation patterns is still a difficult task for several reasons. On one hand, buildings suffer from degradation problems depending on physical and chemical factors, whose causes can be difficult to determine. On the other hand, at the level of data representation, graphic supports need to be defined for deterioration analysis and heterogeneous data manipulation. The goal of this research is to supply experts with a tool for scientific monitoring and decision support so to permit rational programming operations of restorations. This paper proposes an approach for digital documentation of conservation state of buildings (stone alteration, dating, material), permitting to display and cross-reference data related to degradations. This approach will be described through the study case of stones at Chambord Castle.

Weathering of limestone on Al-Ziggurat walls in the ancient Al-Nimrud city (Iraq)

Diagnosing the weathering of stones used in built heritage is essential for their preservation. Samples taken from the surface and the core stones of Al-Ziggurat walls in the archaeological city of Al-Nimrud (North Iraq) were characterized. Stone samples from a quarry believed to be the origin of the stones used in the construction of Al-Nimrud were also characterized. Physical properties, pore space system, mineralogical and chemical compositions and microstructural properties of historic, fresh and weathered stones were determined by various complementary techniques at the microscopic level. Results show that the main damage observed on the stone surface of Al-Ziggurat walls is due to salt weathering. Gypsum is the predominant salt and probably originated from the soil in contact with the stones during burial of the walls. Results also indicate that the characteristics of samples of the core of historic stone are quite similar to those of the fresh stone extracted from the quarry, demonstrating that the core of the historic stone is unweathered and that this quarry was probably the source of the construction material for Al-Ziggurat. This means that these fresh stones could be used in future restoration work.

Kinetics of Stone Degradation of the Castle of Chambord in France

ABSTRACT A multidisciplinary approach combining scientific and historical data is developed in order to identify the environmental factors that cause degradation of stones and to attempt to date the onset of degradation and assess the time needed for its development. The method is applied to the Castle of Chambord, a prestigious monument in the Loire Valley in France. The genesis of the two main types of degradation (spalling and flaking) and the kinetics of their development are identified and analysed. The correlation between the different mappings and iconographic documents reveal that flaking develops on any type of fine limestone and can appear less than 60 years after the stone is placed on the castle for Richemont limestone, and less than 10 years for tuffeau. The other main type of degradation, spalling, is limited to tuffeau, but it is more difficult to quantify the kinetics of its development.