The conservation and preservation of important cultural heritage assets has become a concern of the interdisciplinary scientific community. Current studies illustrate that, through a multidisciplinary approach, in the field of cultural heritage, a cohesive documentation incorporating information regarding not only the architectural and geometric documentation but also historical and archaeological research, building material and decay documentation and structural research provide crucial information regarding the preservation state of a monument, possible conservation interventions and rehabilitation. Since the resources for constructing new buildings in Europe has declined, the scientific and construction community has gained growing interest in restoring and rehabilitating old buildings and monuments [1
]. To achieve sustainable protection and restoration of such assets, a multidisciplinary approach is a prerequisite. In addition, the characterization of building materials and decay is of utmost importance, especially in terms of intervention conservation practices. For the protection of a monument, in most cases, it is forbidden to take samples [1
]. Therefore, the scientific community turns to non-invasive and no-contact practices to acquire the necessary information. In the geometric documentation and architectural documentation field, this practice is performed with the use of laser scanning and image based techniques, keeping the monument intact. For the building materials characterization, non-destructive techniques (NDT) are utilized for the determination of the pathology of a monument. These vast amounts of data can contribute to the protection of cultural heritage assets and also for the decision making on conservation approaches [2
Over the last decade, there is an immerse use of digital documentation processes, especially for the creation of textured three-dimensional (3D) models [6
]. The 3D architectural surveys nowadays utilize techniques provided by surveying and photogrammetric scientific field and use two methodologies: close-range based modeling and image-based modeling [6
]. The first one includes the use of laser scanning techniques to obtain a 3D dense point cloud in the same reference system with below sub-centimeter accuracy [8
]. The other survey includes computer vision algorithms combined with photogrammetric procedures and provides a 3D model with radiometric information importing the texture in the model [10
]. Currently, the scientific community tends to utilize both surveys, especially in cultural heritage documentation where the building materials play a pivotal role in the documentation process. In this case, both survey methods are elaborated and integrated, providing a textured 3D model [12
For the protection of a cultural heritage asset, the classification and representation of a monuments’ pathology aims to control the decay progress and to improve planning of conservation interventions [1
]. Within the framework of cultural heritage assets protection, practical needs emerge regarding the integrated study—management and the knowledge deriving from incompatible interventions towards an interdisciplinary integrated approach. Especially in the case of ancient masonry structures, additional inspection of the monument is necessary and certain factors are important to be obtained.
Nowadays, the research community is beginning to investigate multidisciplinary methods of data acquisition and further elaboration of information in a multispectral, multilateral and multidisciplinary manner. Moreover, the academic community adopts such approaches, especially for the investigation of assets construction phases, deformations and restoration practices, for their visualization and projection in multiple digital platforms. The tendency is to create 3D models (via Geographic Information System (GIS) or Building Information Model (BIM) software) [16
] incorporating information of the abovementioned disciplines as well as other depending on the project’s scope (documentation, visualization, dissemination, restoration etc.).
This study aimed to investigate a multidisciplinary approach, starting from the documentation of multidisciplinary data, which includes their architectural, historical, geometric and building material documentation data, and studying their interrelation for historic building structures, that contributes to the structure’s current state assessment. Using documentation information system, and in particular two-dimensional (2D) maps that derive from the 3D documentation process, in accordance with the use and results of NDT and evaluation (E) techniques, the interdisciplinary diagnosis of decay patterns and their causes can be supported [19
]. Additionally, this approach and the developed thematic maps can facilitate, as the first and crucial step, the planning and application of compatible conservation interventions.
The selected monument for the implementation of this process is the Kaisariani Monastery church. The whole complex consists of Byzantine baths, kitchen, and hearth, reflectory, cells, Benizelos tower and the Catholicon [21
]. The long prosperity of the Kaisariani Monastery is owed to its privileges and fertile surrounding land property. A significant library was located also in the monastery. The devastation of the monastery after the 18th century had a dramatic impact over the church [22
]. The monastery, due to its history, has undergone many construction phases throughout the centuries with three main phases prevailing.
4.1. The Elaboration of the Historical Documentation Towards the Development of Thematic Maps of Construction Phases
As presented in the monument’s construction phases and the restoration interventions (Figure 11
), the Main Church retains the authentic building materials, apart from a specific area located around the door of the northern façade and the two windows of the eastern façade, where a non-documented restoration intervention took place during the 1950s [24
]. Additionally, past and most recent restoration interventions are evident and documented on the west and north exterior walls of the Narthex and the west façade of the chapel. The eastern façade has undergone fewer interventions than the others, while, on the west façade, the restoration interventions cover the entire masonry and there is evidence of repair mortar as well (Figure 11
4.2. Elaboration of NDTs for the Development of Thematic Maps
Since its early construction, the Catholicon has undergone many and various construction interventions, some of which were analytically documented and could be found in the archives of the Local Ephorate of Antiquities. However, the use of NDT is currently utilized by the scientific community to evaluate and assess the compatibility of past conservation–intervention works. The NDT techniques that were applied for the assessment of the church’s current state of preservation indicated surface morphology variations, texture differences and variable surface composition. These variations led to the classification of the building materials and decay data. In addition, areas of increased or reduced emissions were revealed, providing information of structural variation of the masonry, information that was strengthened by the on-site visual inspection of the construction phases and the bibliographic research.
Recording, classification, distribution and representation of building materials on a surface scale, on the monument’s façade, was applied for the exterior of the Catholicon, based on visual inspection and NDT evaluation. The combination of the NDTs resulted in the validation of the building materials and decay pattern classification and therefore was integrated within the CAD information system. In Figure 12
, the classification of the fossiliferous porous stone with 51 cm length and 21 cm width is one of the building materials type encountered in this typical “plinthopericleiston” system of the Catholicon masonry, which includes one layer of stone, one layer of filling mortar and one layer of brick, enclosing each stone. The width of the brick as well as the width of the filing mortar is the same, approximately 2 cm.
On the north façade, integration between DM and IRT results in the validation of different type of construction between the Narthex and the Main Church, since the Narthex is an area of high moisture and, additionally, the susceptibility to bio decay and lichens of the north façade illustrated by DM results is evident (Figure 13
On the east façade, integration of visual inspection and DM images, reveal that 8% of the historical bricks present scaling and material loss just above the rising damp zone, probably due to the presence of the concrete ground work base (Figure 14
4.3. Thematic Maps of Building Material and Decay
Thematic maps of building materials and decay of all the façades were developed. The north and the east façade were chosen since they represent two different states of preservation. In addition, the variation of the construction phases, demonstrated in these façades can contribute to the assessment of the state of preservation, the incompatibility of past restoration works is revealed via the decay thematic map.
In the thematic map of building materials on the north façade of the Catholicon, the variation of materials is evident (Figure 15
). The past restoration works performed in the Narthex of the monument is almost as a patchwork having lost almost completely the structural layer underneath. In the decay thematic map (Figure 16
), the mortar microfractures (brown color) can easily provide information of the incompatibility with other restoration works. Moreover, there is a significant amount of black bio decay (purple color) that covers almost the entire structure.
In the elaborated thematic maps of the east façade, it is evident that its structure consists mainly of building material from the first construction phase with some restoration interventions in the lower zone of the façade (Figure 17
). The main issue that should be dealt is the rising damp as well as the moisture problems in the higher zone of the façade, as illustrated in the thematic map of decay patterns (Figure 18
4.4. Quantitative Data Integration
Through the multidisciplinary process, quantitative and qualitative data were produced and information regarding the preservation state of the monument was obtained. Apart from the visualization of the multidisciplinary data, quantification was possible, providing additional data for further elaboration.
The differences of each façade masonry type were recorded and elaborated for qualitative and quantitative investigation (Figure 19
). The structural system of each façade was documented through the thematic maps, validating the architectural and historical research, their construction period and past restoration works. On the east façade, it is evident that there are a higher percentage of stone and lower ones of mortar in comparison to the other façades, depicting the strict cloisonné system that was followed for its construction. This façade has undergone very few restoration interventions and the structural system of the first construction phase is obvious.
Moreover, bio decay is one of the most deteriorating factors of the Kaisariani Catholicon. A comparative diagram was elaborated, deriving from the thematic map development to quantify and elaborate further the environmental conditions of the surroundings, which can work as a degradation mechanism for the monument (Figure 20
). The north façade presents higher percentages of bio decay in comparison to the other façades, since its orientation favors bio decay growth.
This data quantification process presents many advantages for the planning and application of conservation–restoration interventions. More accurate calculation of the amounts of the required conservation materials can be accomplished, i.e. restoration mortars, and cleaning and protection materials. Therefore, budget and cost analysis of the rehabilitation project can be organized more accurately.
The methodological process is the outcome of this work and is described within this paper. Within this framework, a multidisciplinary approach is presented, importing a vast amount of various data correlated and visualized within thematic maps. The four pillars of this process are the historical documentation, the architectural, the geometric and the building materials and decay documentation (Figure 21
). They all contribute to the creation of multidisciplinary thematic maps and interrelate among each other.
Regarding the four basic pillars of this approach, the preservation state in terms of building materials pathology is illustrated and is in conjunction with the geometric and architectural documentation data. The past restoration works are depicted including the various construction phases of the monument (historical documentation), ensuring sustainability in terms of planning and applying of conservation and restoration interventions. Each documentation process contributes equally in the illustrated diagram for the creation of the multidisciplinary thematic maps.
Through this proposed process, it is important to follow specific steps that can lead eventually to the protection of the cultural heritage asset. The recording of the current state of preservation is among the initial and most crucial steps. In the Catholicon of Kaisariani, this was a very demanding task, since the Ministry of Culture did not give permission to perform analytical documentation processes in order to have all the relevant information, due to its high significance. Therefore, the documentation process of the historical data was crucial for the assessment of the construction phases of the monument and also document past restoration projects that were recorded.
In addition, the construction style of the monument aligns with the era that was built (brick and stone cloisonné masonry style). The geometric documentation provided information regarding the structural system, including building materials dimensions (width and length) in the exterior façades, as well as information regarding the structural section dimensions of the walls, validating the documented construction phases Moreover, correlation between geometric and architectural documentation depicted alterations of the monument through time, including deviation from the vertical and alteration in the structures’ surface. A 10-cm deviation from vertical in the St. Antonio’s Chapel is an example of deformation that can occur in the case of structures constructed in different periods, with different types of materials, etc. Information regarding the pathology of the building in terms of exterior decay factors is highlighted within thematic maps incorporating geometric, architectural and building material data investigation. The north façade presents high interest since it incorporates information of the first construction phase of the Catholicon, with the strict cloisonné system and main decay factor, the bio decay that accumulates due to environmental factors and location.
Through this investigation, the proposed processes, address various disciplines and stakeholders and utilize the thematic maps development. Through these thematic maps, whether they address the construction phases, building materials or restoration works, a correlation and management of the various disciplinary information is accomplished, contributing to the planning of interventions, if and when the need arises.
The presented processes are multidisciplinary tasks that require collaboration among architects, surveyor engineers and materials scientists/engineers (Figure 22
). To conclude, the proposed methodological processes can be implemented for all cultural heritage assets to determine the preservation state and facilitate decision making for sustainable protection. In the specific case of the Catholicon of Kaisariani that was investigated for the development of the proposed process, permission was given only for the study of the exterior façades of the monument in terms of building material and decay characterization. Issues concerning the stratigraphy of the structure and other parts of the Catholicon such as the interior and the roof could be a next step of study whenever permission is given by the Ministry of Culture.