that these deteriorations are generally found on sedimentary and volcanic stones, due to inhomogeneities in physical or chemical properties of the stone such as heterogeneous stones containing harder and/or less porous zones. Salt crust formations can also be observed in lower parts of the northeastern façade that are washed by the waves. Besides, calcite encrustation linked to water leached from joints is seen on this façade (ICOMOS 2008). On the other hand, the samples taken from the places where visitors lit fire such as the northeast façade and the cistern have sulfate and carbonate besides chlorine. Discolouration can be observed in these areas as a result of being exposed to fire. Besides, the presence of protein and oil on the samples M6 and M8 can be related to the action of visitors and some biological formations. These results show that measures should be taken to preserve the building against vandalism.
As intervention proposal, stuccoes can be employed which are composed of stone itself (crushed) and lime (Torraca 2005) for the stones highlighted on the mapping with the deterioration types differential erosion and alveolization, while the ones highlighted with coving can be integrated with natural 51stones of same type from the source in the area. Mechanical cleaning methods can be suggested for the deteriorations such as salt crust and calcite encrustation. For deteriorations such as discoloration and graffiti, several cleaning methods should be examined for each case before implementation phase. For biological formations such as lichens, an interdisciplinary research is needed.
Table 3: Macroscopic and microscopic views of stone samples from Rumelifeneri Fortress. (B: Binder, A: Aggregate, CA: Calcareous Aggregate, PBW: Physically Bound Water, SBW: Structurally Bound Water, Ct: Calcite, Q: Quartz, V: Volcanic, C: Carbonates/Limestone, F: Feldspars, B: Brick particles and dust).
Table 4: Results of water soluble salts, protein, oil and conductivity analysis. (–: Undet., +: Small amt., ++: Pres., +++: Large amt., ++++: Abun.).
A color difference on courtyard level could be observed on masonry mortars of the façades facing the sea. Masonry mortars below this level are yellowish (M1 and M3) while the ones above are whitish (M4). This difference could be seen also in test results (B : A ratios, sieve analysis, aggregate distribution). According to the observations, not only M1 and M3 but also M10 have similar properties, and this fact can be evaluated as a hint for explaining the phases of the construction process. On the other hand, M2 can be re-evaluated as a joint or repair mortar as it has different properties from M1 and M3, despite being below the courtyard level. Besides, M5, M6 and M7 were taken from brick masonry parts have the same B : A ratio and similar aggregate properties. This indicates that the same mortar was used in those parts.
Ignition loss and acid loss tests results indicated that lime was used as binder in all of the mortar samples. As a result of macroscopic and microscopic observations on aggregates, mortar samples have mostly volcanic rocks, quartz, feldspars and meshed brick as aggregate in different sizes.
Despite its conservation problems, Rumelifeneri Fortress has also several advantages. As the northern part of the Bosporus has the same geology, similar building materials were used in the construction of northern Bosporus fortresses from 52both European and Asian sides such as Garipçe, Poyraz, Kilyos and Riva (Akgür 2015). Thus, similar deteriorations and conservation problems are encountered in these buildings. As a result of this situation, the mapping and glossary prepared in this study can be taken as a reference for other fortresses of the zone for material and deterioration analysis and also intervention proposals. Besides, as Rumelifeneri Fortress was built on its building stone sources, there is no problem with supplying original material for its restoration and conservation works. On the other hand, this source area can be used as a laboratory for monitoring the results of several intervention methods and defining the correct methods for conservation works. All in all, Rumelifeneri Fortress can be chosen as a pilot area to preserve Bosporus fortresses and the intervention methods should be monitored on the natural stone source area which is facing the same conditions (weather, sea salts, visitors, etc.) as the fortress. After ascertaining the suitable intervention methods on the source area and necessary awareness raising activities, conservation and restoration works shall start on Rumelifeneri Fortress and the other fortresses of Bosporus.
Acknowledgements
We thank Burcu Bas, er Gürer, Ph. D. student from Istanbul Technical University, Faculty of Architecture for her contributions at the beginning of the study, Dr. O. Serkan Angı from ITU, Faculty of Mines for his precious support for our studies and Prof. Dr. Lütfi Öveçoğlu from ITU, Faculty of Chemical and Metallurgical Engineering and his laboratory team for their support about SEM-EDS analysis in their laboratories.
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