Sarah Janvier-Badosa

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.

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.

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.

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.

Non-destructive diagnosis by colorimetry of building stone subjected to high temperatures

When a building is exposed to fire, the building materials are subjected to high temperatures which cause changes in their structural and aesthetic properties. As the replacement of degraded stones is expensive, a diagnosis of degradation by using non-destructive tests could help to select the appropriate restoration method. The objective of this study is to propose an in situ methodology to assess the state of degradation of stone after exposure to fire by providing a relationship between the state of damage of the stone and its colorimetric properties. Laboratory tests were performed on tuffeau limestone, heated at different temperatures, from 100 to 900 °C. Colorimetric measurements were compared to another non-destructive test, ultrasonic P-wave velocity measurements, which are widely used for damage diagnosis of concrete structures.

The Valmod Project: Historical and Realistic 3D Models for the Touristic Development of the Château de Chambord

The Valmod project is a French regional scientific program whose objective is to propose innovative scenarios for the tourist development of built heritage from the combined contribution of in situ 3D acquisitions, informatics, and history. This interdisciplinary approach aims to stage original historical content thanks to appropriate 3D models and the use of adequate media for the targeted public. This communication presents several examples selected among the applications developed during this program: the creation of a global model able to precisely describe the whole architecture of the Château de Chambord; a 3D print of the double staircase that can be unscrewed to separate the two stairways; replicas of pieces of the lapidary deposit to make them virtually easy to handle. The challenges concern both technical aspects such as the precise registration of thousands of multi-scale scans or the creation of manifold meshes from point clouds, and project management aspects such as making the interdisciplinary approach effective.

The SACRE Project: A Diagnosis Tool of Built Heritage

The SACRE project is a research project which aims to create a tool to help the professionals in charge of preservation and restoration of cultural heritage buildings. The objective of this project was to develop a working methodology and create the technological tools necessary to implement this methodology. This project describes the steps the development of the digital health record of a building. This project focused on the study and understanding of the mechanisms of degradation of limestone, the main material for building construction. The Castle of Chambord was chosen to be the subject of this study.