A Multi-Analytical Study of Historical Materials from the Old Armenian Church in Türkiye

Abstract

Historic structures that possess cultural heritage value are important documents that convey the architectural understanding, material technology, and construction techniques of past civilizations to the present day. However, these structures are exposed over time to physical, chemical, and mechanical deterioration due to environmental effects, climatic conditions, the natural aging processes of materials, and human interventions. The conservation and faithful restoration of historic structures necessitate the scientific determination of the properties of original building materials. In this study, we aimed to determine the physical, chemical, mineralogical, thermal, and mechanical properties of the original building materials used in the Old Armenian Church located in the city of Çanakkale. In order to reveal the chemical and mineralogical compositions of the samples, XRD, SEM, Raman, and FTIR analyses were applied. The thermal behaviors of the materials were examined through TGA. To determine the physical properties, tests for unit volume weight, specific gravity, compactness, porosity, and water absorption capacity were carried out. For the determination of mechanical properties, compressive strength tests—as well as non-destructive testing methods such as the Schmidt hammer and UPV measurements—were employed. The analysis results indicate that the materials used in the structure have a carbonate-based mineralogical composition and that calcite-bonded systems are dominant. While the physical and mechanical data reveal that the materials possess a compact internal structure, they also indicate that microcracks and weathering processes may be effective in certain areas. These findings emphasize the importance of using lime-based mortars and stones compatible with the original materials in restoration works.

1. Introduction

Historical structures are places of memory that embody the heritage of past civilizations and reflect the collective cultural accumulation of societies across generations. As emphasized by the UNESCO World Heritage Convention, heritage is the set of common values that have been transmitted from the past to the present, continue to exist, and must be passed on to future generations [1]. The significance of historical structures stems from their historical, cultural, and spatial characteristics. A monument or structure can simultaneously address various value categories through its architectural and artistic qualities, historical background, spiritual function, and social–urban context. St. Paul’s Chapel in New York, built in 1766, assumes an aesthetic value through its architectural features, a historical value due to its association with George Washington, a spiritual value through its function as a place of worship, and a social and economic role through the continuity of its use and its urban location [2].

Located at the intersection of Europe and Asia, Türkiye has hosted the development of many civilizations thanks to its geopolitical position and thousands of years of settlement history, which has endowed the country with a rich cultural heritage. The province of Çanakkale, situated in the northwestern part of Türkiye, has historically been an important passageway through the Dardanelles Strait, which connects the Asian and European continents as well as the Mediterranean and the Black Sea. Due to this strategic location, the region has hosted continuous settlements throughout history [1,3]. Distinguished by its history extending from ancient times to the present, the region bears the traces of many civilizations such as the Lydians, Persians, Romans, Byzantines, and Ottomans. Numerous archaeological sites and cultural assets in the region, most notably the Ancient City of Troy, which is the subject of Homer’s Iliad, demonstrate that Çanakkale has been a crossroads of different civilizations [4].

The fundamental basis of studies aimed at the conservation of historical structures is the necessity to preserve the original materials and characteristics of these monuments, which are sensitive to various internal and external factors over time. However, the original materials of these structures deteriorate over time due not only to natural aging processes but also to environmental conditions and human-induced factors. Atmospheric effects such as freeze–thaw cycles occurring under certain climatic conditions, salt crystallization, corrosion, and wetting–drying processes weaken the microstructural integrity of porous building materials such as brick and stone, leading to physical and chemical damage [5,6,7,8]. Salt crystallization is one of the major deterioration mechanisms that causes the propagation of cracks and a reduction in material strength through internal stresses generated during crystal growth in porous building materials [9]. Environmental pollution originating from urban and industrial sources also has negative effects on the physical and chemical integrity of historical structures. Pollutants such as heavy metals, sulfur and nitrogen oxides, and particulate matter accumulate on building surfaces, accelerating chemical decomposition processes that lead to the formation of acidic compounds and to darkening and surface deterioration defined as black crust. These pollutants can cause transformations in the original physical and chemical properties of building materials [8,10,11].

The conservation of historical structures requires an interdisciplinary approach. Contemporary conservation principles emphasize that interventions should be kept at a level that preserves the authenticity of the structure. Various studies have demonstrated that repair practices carried out in the past with insufficient awareness or with materials incompatible with the original structure have caused damage to these buildings. Excessive interventions in earlier periods and restoration applications incompatible with the original materials have weakened the structural integrity of historical structures and accelerated the deterioration process [12,13,14,15,16]. These negative examples of intervention have clearly demonstrated the importance of the principle of minimum intervention and the necessity of adopting restoration approaches compatible with original materials and techniques in conservation studies. Today, international conservation standards also support this approach. In key documents and principles such as the 1964 Venice Charter, the importance of applying techniques based on scientific methods in the conservation and restoration of cultural heritage is emphasized [14,17].

In the conservation of historical structures, it is of great importance that the intervention process is based on scientific principles, that building materials are analyzed comprehensively, and that the causes of deterioration are accurately diagnosed. It is understood that interventions carried out without considering the original structural and chemical properties of the materials can negatively affect the historical integrity of the structure, making decision-making based on scientific analyses essential in conservation practices [18]. In this context, it has been observed that laboratory-based material analyses have become increasingly common in recent years in the conservation of historical structures. The analysis of the physical, chemical, mineralogical, and mechanical properties of historic building materials is a decisive factor in the conservation and restoration process, as it allows for the assessment of the current level of deterioration and the prediction of future behavior of the materials. This characterization process enables the determination of intervention methods according to the material’s needs, facilitating the development of effective and sustainable conservation strategies specific to each structure [14,16,19,20].

Today, a wide range of advanced analytical methods and instruments are used in the characterization of historical building materials to determine their various physical and chemical properties. Commonly employed techniques include: scanning electron microscopy (SEM) and the associated energy-dispersive X-ray spectrometer (EDS) for microstructure and elemental composition analyses; X-ray diffraction (XRD) for the identification of crystal structures and mineral phases; X-ray fluorescence (XRF) for quantitative determination of elemental composition; Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy for identifying molecular structures and chemical bonds; and thermogravimetric analysis (TGA) for evaluating thermal behavior and weight loss related to material components. Each of these methods provides information on a specific aspect of the building material, and when used together, they offer a comprehensive profile of the material. Using SEM, the porosity, particle size distribution, and microcrack formation in mortar or stone samples can be analyzed, while XRD applied to the same samples can identify mineral phases such as calcite, quartz, and feldspar. FTIR and Raman analyses provide information on functional groups and amorphous structures in the material, whereas TGA data are used to evaluate thermal properties such as the degree of carbonation or bound water content. In this context, laboratory analyses allow for a detailed assessment of the chemical composition and physical structure of historical building materials [14,21,22,23,24,25,26,27,28,29].

In the assessment of historical structures, non-destructive testing (NDT) methods, which do not damage the building, are employed. In situations where sampling opportunities are limited, techniques such as the Schmidt hammer and ultrasonic pulse velocity (UPV) measurements are commonly used to determine the in situ mechanical properties of materials. The Schmidt hammer estimates compressive strength based on rebound values related to surface hardness, while the UPV method measures the speed of sound waves passing through the material, providing information on its elastic properties and overall integrity. These methods are particularly important for assessing the strength distribution, homogeneity, and deterioration that develops over time in historic brick and stone units. When the results of these tests are combined with laboratory analyses, a more comprehensive evaluation of the performance of building materials can be achieved [27,29,30,31,32,33,34].

In the study conducted by Jordán et al. [35], the quantitative analytical potential of the FTIR method in determining the mineralogical components of historic mortars was investigated. FTIR measurements performed on pure minerals and various mixtures were used to calculate the relative absorption intensities of the minerals with respect to the main calcite band. The obtained data were compared with XRF and XRD analyses, and it was observed that these methods, when used together, could reliably reveal the actual composition of mortars. The study concluded that the FTIR method, when combined with appropriate regression models, can provide a rapid and low-cost semi-quantitative analysis of historic mortars. In the study conducted by Uygun [36], the building materials of the Kaya Bey, İbrahim Bey, and Halhallı mosques in Balıkesir were examined. Physical, chemical, petrographic, and mechanical analyses revealed that andesite and micritic limestone were used in the Kaya Bey Mosque, andesite and tuff in the İbrahim Bey Mosque, and andesite and dolomitic marble in the Halhallı Mosque. It was determined that the mortars contained volcanic rock and schist aggregates, with the binder ratio generally around 20–25%. Additionally, the presence of nitrate and chloride salts was detected in some samples. İş [37] investigated the characteristic properties of mortars and plasters from the Byzantine and Ottoman periods in the İmaret-i Atik Mosque. Işık [38] examined 29 mortar and plaster samples taken from Hellenistic and Roman structures in the Ancient City of Aspendos, applying mineralogical methods such as XRD, SEM/EDX, and thermal analyses, alongside physical and chemical tests. The results indicated that the densities of the mortars ranged from 1.15 to 1.83 g/cm³, and the porosity rates ranged between 21% and 51%. Owsiak [39] analyzed mortar samples from 13th-century historical structures using SEM-EDS, finding that all mortars contained fully carbonated lime-based binders and that the aggregates were largely composed of quartz sand. Other minerals identified within the aggregates included flint, limestone, sandstone, and feldspar. Qian et al. [26] reported that the dominant minerals in mortar samples from the ancient city wall of Xindeng in China were calcite and quartz. Similarly, Santhanam ve Ramados [40] determined that the mortars used in Alamparai Fort in India were air-lime binders with siliceous sand aggregates. Ponce-Antón et al. [28] observed that lime mortars used in the city walls of Burgos, Spain, had different compositions across different periods. Carvalho et al. [41] found that mortars in the Alcobaça Monastery in Portugal contained quartz, kaolinite, and feldspar minerals and were produced from local raw materials. Likewise, Medeghini et al. [42] examined ancient mortars used in the Aqua Traiana aqueduct in Rome and developed new, environmentally friendly restoration mortars with similar properties. Loke et al. [43] proposed a systematic mixing method for the design of traditional lime-based mortars. Bilgilioğlu [44], by comparing original and restoration mortars from Tyana Church, revealed that some restoration mortars used dolomitic lime binders, which could lead to long-term durability issues.

Numerous scientific studies conducted worldwide have made significant contributions to the literature by analyzing the building materials of historical structures from different periods and cultural contexts. These studies are valuable in demonstrating the validity of the applied analytical methods and in identifying the original characteristics of building materials across various geographic and historical scales. Despite numerous studies on historic building materials, most focus on limited analytical techniques or isolated property assessments. In contrast, this study presents an integrated approach by jointly evaluating the physical, chemical, mineralogical, thermal, and mechanical properties of original materials from the Old Armenian Church in Çanakkale. Advanced techniques (XRD, SEM, Raman, FTIR, TGA) are combined with both destructive and non-destructive methods, enabling a multi-scale characterization. The findings obtained within the scope of this research are expected to provide a scientific basis for decision-making in the conservation of the structure and in future restoration practices.

2. The Old Armenian Church

The Old Armenian Church is located in the Fevzi Paşa Neighborhood of the city center of Çanakkale, Türkiye (Figure 1). Different information regarding the construction date of the building appears in the literature. Historical sources indicate that the church was built in 1873. However, in the study by Koyuncu [45], it is stated that the construction date is not sufficiently supported by historical data and remains a subject of debate. The same study, based on Armenian monastery archives, suggests that the existence of the building dates back to the second half of the 17th century. It is reported that the church was first constructed in 1718, during the reign of Sultan Ahmed III, on the site of an older church. According to Ottoman archival documents from 1831, the building was repaired during the reign of Sultan Mahmud II, and following the repairs carried out between 1831 and 1832, no further alterations were made until 1888. In contrast, Tombul [46], based on archival records and historical documents, states that the church was commissioned in 1873 by Sultan Abdülaziz for the Armenian community living in the Ottoman Empire. The building, which lost its original function as the Armenian population declined, was used as the Çanakkale Archaeological Museum between 1934 and 1984. After restoration works carried out by the Ministry of Culture in 1984, the structure was used as a theater hall until 1997. Following further repairs and maintenance by the Ministry of Culture in 1997, the building was again used as a museum in 2000 and was finally allocated to Çanakkale Onsekiz Mart University in 2005.

The church was constructed with a rectangular floor plan, oriented along the east–west axis. The ground and mezzanine floor plans of the building are shown in Figure 2 and Figure 3. These plans were reconstructed based on the available technical drawings. The main entrance façade (west façade) of the church measures 16.60 m in length, while the side façades (north and south façades) measure 25.30 m. The façade arrangement, characterized by symmetrically placed windows, a vertical emphasis, pointed-arch openings, and stone moldings, indicates that the structure was built under Neo-Gothic influences.

The main entrance façade has been covered with finely cut stones during later restoration works. At the center, there is a pointed-arch door, above which is a circular window, and above the window, a triangular architectural design extends along the lintel. On either side of the door, there are four pointed-arch windows. The main entrance façade is shown in Figure 4a. Examination of the side façades reveals the use of sandstone and brick. The north and south façades have been preserved in their original state, featuring three arched windows constructed with stone and brick at the lower level and a single circular window at the upper level. The sections of these façades facing the main entrance are covered with plaster, partially concealing the original texture. Near the eastern end of the north façade, a building is indicated, which appears to have collapsed over time. On the south façade near the eastern end, there is a room providing access through a door. At the corner junctions where the side façades intersect with the main entrance façade, cut stone moldings have been used to add visual fullness. Images of the south and north façades are shown in Figure 4b and Figure 4c, respectively. The rear (east) façade is defined by a semicircular projection at its central section, symbolizing the direction of worship. Overall, horizontal moldings at upper levels and along the eaves, along with cornice details, provide depth in the horizontal direction and are important elements that enhance the architectural aesthetics of the church.

Examination of the building’s interior reveals that it consists of a single nave. All walls are covered with plaster and painted white, giving the interior a spacious appearance. Upon entering from the main entrance façade, there is a 7 m² entrance hall immediately in front of the wooden exterior door. On the right and left sides of the hall, there are two rooms divided by wooden partitions. The building, constructed as a two-story structure, features a mezzanine floor on the second level. The mezzanine is situated 4.80 m above the ground and provides 100 m² of usable space. Access to the mezzanine is via a spiral staircase consisting of 25 wooden steps. The mezzanine, supported by two wooden columns from the ground, is entirely constructed of wood. The main hall of the building has an area of 235 m². The ceiling of the main hall is sloped and covered entirely with white-painted wooden material. The arched windows on the side walls are arranged at regular intervals, positioned high and wide, allowing natural light to enter and distribute evenly throughout the interior. On the east façade of the hall, there is a stage area 1 m above the floor, covering 55 m². The apse-like niche in this area is undecorated, while smaller niches on either side maintain the overall symmetrical effect of the interior. Images of the interior are shown in Figure 4e,f.

Today, upon examining the building, numerous signs of deformation have been observed. The sections of the north and south façades near the west façade have been covered with a yellow-painted plaster, as seen in Figure 4b,c. This plaster layer exhibits widespread bulging, detachment, and cracking. As shown in Figure 5, moss growth is present on the north and south façades. Moss colonization is a type of biological deterioration that occurs in damp environments. Depending on environmental factors, this deterioration typically develops in the lower regions of the walls, closer to the ground [47]. Moss growth observed in joints and on stone surfaces can lead to the formation of cracks and fissures. Additionally, enzymes produced by the moss can cause surface deterioration, which negatively affects the load-bearing system and the overall structure of the building [6].

Another deformation observed in the building, as shown in Figure 6, is the rusting of iron elements on the exterior façades, which has caused rust stains. Rusting is a type of chemical deterioration, and the primary factors contributing to this degradation are moisture and temperature [6,48].

In the building, as shown in Figure 7, cracks, breakages, and material loss are observed in the decorative elements, reliefs, and eaves. These deteriorations generally occur due to freeze–thaw cycles and surface water runoff. Additionally, considering that the city of Çanakkale is located on a seismic fault line, the formation of cracks and deformations over time is inevitable.

In many parts of the building, openings in the joints between stone and brick and losses of mortar are observed. Additionally, as shown in Figure 8, numerous signs of repairs and interventions are present. These interventions were carried out using cement-based mortar patches, which disrupt the structural texture of the building and compromise the original character of the stone materials used.

3. Experimental Program

3.1. Materials

At the Old Armenian Church, it was determined that sandstone and brick were used together on the north and south façades, while sandstone predominates on the east façade. During the sampling process, areas where subsequent interventions were made were excluded as much as possible, and samples were taken from regions that were considered to represent the original material character. Samples were obtained in limited numbers from the unrestored original parts of the building without causing any damage to the structure. To determine the properties of the materials used, a total of five samples were collected to represent the entire building: two sandstone samples, two mortar samples, and one brick sample. In this study, the sandstone samples were labeled S1 and S2, the mortar samples M1 and M2, and the brick sample B. Images of the collected samples are presented in Figure 9. Figure 9a,b show the mortar samples, Figure 9c,d show the two different sandstone samples, and Figure 9e shows the brick sample. To determine the compressive strength and physical properties of the stone material, 50 mm cubic samples were obtained from the existing collapsed sandstone (Figure 10).

3.2. Methods

To determine the mineralogical composition and examine the microstructural properties of the materials, XRD, FTIR, SEM, and Raman spectroscopy analyses were conducted, while TGA was performed to determine their thermal properties. XRD analysis was performed using a PANalytical Empyrean (Malvern Panalytical, Almelo, The Netherlands) diffractometer. A Cu Kaα radiation (λ = 1,54 Å) source operating at 45 kV and 40 mA was used. Diffraction data were collected over a 2θ range of 5–70°, with a step width of 0.02°. FTIR spectra measurements were conducted within the wavelength range of 4000 cm⁻¹ to 400 cm⁻¹, with a resolution of 4 cm⁻¹, and a total of 32 scans were performed, using a Perkin Elmer Spectrum Two FTIR spectrometer (PerkinElmer Inc., Waltham, MA, USA). The Raman spectroscopy was performed with a WITEC ALPHA 300RA model (WITec GmbH, Ulm, Germany) device with a 532 nm laser wavelength, which works according to the method of inelastic scattering of light incident on bonds within the molecule. TGA was performed with a Perkin Elmer TGA 8000 device to determine the thermal properties of the samples. The samples were prepared as follows: 10.5 mg in dry and powder form and heated from 30 °C to 900 °C at an increase rate of 10 °C/min. Surface morphology was characterized by SEM analysis using a JEOL electron microscope (JEOL Ltd., Tokyo, Japan).

The physical properties of the materials, including the unit weight, specific gravity, compacity, porosity, and water absorption capacity, were determined. The unit weight value was calculated according to Equation (1), where $W_k$ represents the dry weight of the sample, and $V$ represents its total volume.

$$\Delta ={\displaystyle \frac{W_k}{V}}$$

(1)

The specific gravity value was calculated according to Equation (2), where $W_1$ represents the dry weight of the powdered sample, $W_2$ represents the weight of the container filled with water, and $W_3$ represents the weight of the container filled with both water and the powdered sample.

$$\delta ={\displaystyle \frac{W_1}{W_1+W_2-W_3}}$$

(2)

The compacity and porosity values were calculated according to Equations (3) and (4), respectively, where Δ represents the unit weight, and $\delta$ represents the specific gravity.

$$k=\left({\displaystyle \frac{\Delta }{\delta }}\right)\times 100$$

(3)

$$\rho =\left(1-{\displaystyle \frac{\Delta }{\delta }}\right)\times 100$$

(4)

The water absorption rate was calculated according to Equation (5), where $W_d$ represents the water-saturated weight of the sample, and $W_k$ represents the dry weight of the sample.

$$\alpha ={\displaystyle \frac{W_d-W_k}{W_k}}$$

(5)

To determine the mechanical properties of the materials, three different testing methods—the compressive strength test, the Schmidt hammer test, and the UPV test—were used. The compressive strength test was carried out in accordance with the TS EN 12390-3 Standard, the Schmidt hammer test in accordance with the TS EN 12504-2 Standard, and the ultrasonic pulse velocity test in accordance with the TS EN 12504-4 Standard. Images of the measurements taken are provided in Figure 11.

4. Results and Discussion

4.1. XRD Analysis

The XRD results of the M1, M2, S1, S2, and B samples collected from the Old Armenian Church are shown in Figure 12. According to the XRD analysis of sample M1, the dominant mineral is calcite. In addition, a significant amount of quartz was also detected in M1. The XRD result of sample M2 shows that calcite is the dominant mineral. Additionally, quartz, gypsum, and albite minerals were identified in M2. For the S1 sample, XRD analysis indicates that calcite is the dominant mineral, with a significant presence of quartz as well. The XRD result of S2 shows that calcite is the dominant mineral, along with quartz and dolomite. The XRD analysis of sample B reveals that the dominant mineral is quartz. Furthermore, the B sample contains a high amount of albite and a significant amount of hematite.

Calcite and dolomite minerals are commonly found in materials used in historic structures. These minerals contribute to strength through carbonation reactions while also enhancing the material’s resistance to atmospheric conditions, thereby increasing the durability of the buildings. Researchers have noted that lime-enriched materials provide more lasting protection against fluctuations in moisture and temperature. Quartz, due to its hardness, increases the resistance of materials to abrasion [25,26,41,49]. Hematite is an iron oxide mineral commonly detected in historic building materials and surface crusts. It is particularly transported to monumental structures via aerosol-derived particles, contributing to surface coloration and crust formation [50]. The presence of hematite in historic bricks and mortars indicates oxidizing firing conditions and the use of iron-rich raw materials, which influence the reddish tones, durability, and long-term deterioration behavior of the material [51,52]. Albite belongs to the feldspar group of minerals [53]. It is commonly observed in magmatic and metamorphic rocks and, especially in granitic systems, serves as an important indicator mineral for evaluating rock formation processes and geochemical evolution [54].

4.2. FTIR Analysis

FTIR spectra in the range of 400–4000 cm⁻¹ were recorded for the M1, M2, S1, S2, and B samples collected from the Armenian Church. The FTIR spectra for these samples are shown in Figure 13.

The FTIR spectrum of sample M1 shows a band at 1411 cm⁻¹ corresponding to the asymmetric stretching vibration of the CO₃²⁻ group, while the bands at 873 cm⁻¹ and 712 cm⁻¹ represent the bending vibrations of carbonate, confirming the presence of calcite [55,56]. The Si–O stretching vibration observed around 1000 cm⁻¹ and the low-frequency lattice vibrations at 403 cm⁻¹ are consistent with the characteristic silicate bands of quartz (SiO₂). In the FTIR spectrum of sample M2, the 1411 cm⁻¹ band indicates the asymmetric stretching of the CO₃²⁻ group, and the 873 cm⁻¹ band corresponds to the bending vibration of carbonate, confirming calcite presence [56,57]. The Si–O vibrations at 777 cm⁻¹ and 695 cm⁻¹, along with the Si–O–Si bending vibration near 450 cm⁻¹, match the characteristic quartz bands [58]. Vibrations observed around 1000 cm⁻¹ overlap with SO₄²⁻ group vibrations, supporting the presence of gypsum identified by XRD [59]. The silicate bands in this spectrum also align with the albite (feldspar) phase detected in XRD results. For sample S1, the 1416 cm⁻¹ band corresponds to the asymmetric stretching of CO₃²⁻, and the 872 cm⁻¹ and 712 cm⁻¹ bands correspond to carbonate bending vibrations, confirming calcite. The 1012 cm⁻¹ band (Si–O stretching) and ~435 cm⁻¹ band (Si–O–Si bending) correspond to the characteristic silicate bands of quartz. The FTIR spectrum of S2 shows the 1417 cm⁻¹ band (CO₃²⁻ asymmetric stretching) and 873 cm⁻¹ and 713 cm⁻¹ bands (carbonate bending), indicating the presence of carbonate minerals. These bands occur in regions common to both calcite and dolomite, confirming the presence of a carbonate phase, though differentiation between carbonate types is limited [60]. The Si–O stretching around 1000 cm⁻¹ and Si–O bending near 406 cm⁻¹ correspond to quartz silicate bands. For sample B, the 777 cm⁻¹ band and low-frequency lattice vibration near 428 cm⁻¹ correspond to characteristic quartz silicate bands. The Si–O stretching vibration around 1000 cm⁻¹ indicates aluminosilicate phases in the brick, consistent with albite (feldspar) identified in XRD analysis [61]. The absence of prominent carbonate bands in the spectrum supports that the sample does not contain a carbonate-based binder and that its mineralogical composition is predominantly silicate/aluminosilicate phases. The hematite phase detected in XRD reflects the presence of iron oxide in the brick, though it may not appear as a distinct peak in FTIR due to weak or overlapping bands. Overall, the FTIR results confirm the mineral phases identified in the samples and are consistent with the XRD analysis. The carbonate bands observed support the presence of calcite in the samples, while the Si–O and Si–O–Si vibration bands indicate the presence of quartz and feldspar-group silicate minerals. Additionally, the sulfate vibrations observed in sample M2 support the presence of gypsum identified by XRD.

4.3. Raman Spectroscopy

The Raman spectra of the M1, M2, S1, S2, and B samples collected from the Armenian Church are shown in Figure 14. In the spectra of samples M1, M2, and S2, two distinct peaks are observed at 719 cm⁻¹ and 1090 cm⁻¹. These peaks correspond to dolomite and calcite minerals, respectively. In Raman spectroscopy studies, bands observed around 1085–1090 cm⁻¹ are attributed to the symmetric stretching vibrations of the carbonate group and are recognized as characteristic Raman bands for identifying carbonate minerals [62]. The band observed near 719 cm⁻¹ is a characteristic vibration of dolomite and serves as an important indicator for distinguishing carbonate minerals [63]. Therefore, the Raman bands identified in M1, M2, and S2 confirm the presence of carbonate minerals in these samples. For sample S1, the peak at 1090 cm⁻¹ represents calcite. Literature reports indicate that the 1085–1090 cm⁻¹ bands in calcite Raman spectra arise from the symmetric stretching vibration of the carbonate ion and are considered the characteristic Raman peak of calcite [62]. The observed peak in S1 aligns with this finding. In the spectrum of sample B, four distinct peaks are observed at 414 cm⁻¹, 506 cm⁻¹, 678 cm⁻¹, and 1339 cm⁻¹, corresponding to albite, hematite, gypsum, and amorphous carbon, respectively. Raman studies indicate that bands in the 400–420 cm⁻¹ range are associated with Si–O vibrations in feldspar-group minerals and are important for feldspar identification [64]. Bands near 500 cm⁻¹ correspond to vibration modes of hematite, and bands between 667 and 680 cm⁻¹ are characteristic Raman bands of gypsum within sulfate minerals [63,65]. The bands observed around 1330–1340 cm⁻¹ are generally associated with D-bands in the Raman spectra of amorphous carbon or carbon-containing phases [62]. In summary, the Raman bands identified in sample B indicate that the sample contains mineral phases including silicates, sulfates, and iron oxides.

4.4. TGA

The TGA results for the M1, M2, S1, S2, and B samples from the Old Armenian Church are presented in Figure 15.

According to the results, the weight losses at 200 °C for M1, M2, S1, S2, and B were 3.00%, 3.40%, 0.31%, 0.26%, and 0.38%, respectively. These values indicate that the moisture content in the samples is low. Between 100 and 200 °C, adsorbed water evaporates, and previous studies have reported weight losses of 1–3% in most materials, reaching up to 5% in samples with higher moisture content [52,66,67]. At 600 °C, the weight losses for M1, M2, S1, S2, and B were 10.73%, 7.12%, 1.91%, 0.72%, and 1.12%, respectively. These values suggest that the clay mineral content in the samples is low. Dehydration of clay minerals occurs between 200 and 600 °C, and previous studies have reported weight losses of 4–10%, with an average around 8% [53,68]. At 900 °C, the weight losses for M1, M2, S1, S2, and B were 21.54%, 19.49%, 41.84%, 41.70%, and 1.83%, respectively. These results indicate a very high calcite content in the samples. Between 600 and 900 °C, calcite (CaCO₃) decomposes, releasing a large amount of CO₂, which results in weight losses of 20–40% as reported in previous studies [25,69,70].

4.5. SEM Analysis

The SEM images of the M1, M2, S1, S2, and B samples collected from the Old Armenian Church are presented in Figure 16, Figure 17 and Figure 18. As shown in Figure 16, the structure of sample M1 contains calcite and quartz minerals. Sample M2 was found to contain calcite, quartz, gypsum, and albite. In Figure 17, S1 contains calcite and quartz, while S2 contains calcite, quartz, and dolomite. As shown in Figure 18, sample B contains quartz, albite, and hematite. In interpreting the crystal morphologies observed in the SEM images, reference was made to mineral morphologies reported in the literature. Accordingly, literature sources define the morphologies as follows: angular and rhombohedral crystals correspond to calcite; irregular fractured surfaces correspond to quartz crystals; rhombohedral morphologies indicate dolomite crystals; needle-like and prismatic crystal aggregates correspond to diopside; spherical or semi-spherical structures correspond to hematite; tabular and prismatic crystal forms correspond to albite; and plate-like or fibrous crystal structures correspond to gypsum [71,72,73,74,75,76].

When the results obtained from different analytical techniques are evaluated in terms of their complementarity, cost, and labor requirements, XRD analysis provides the primary and most critical information for phase identification, while FTIR and Raman analyses offer complementary data for confirming similar mineralogical features. Although these spectroscopic methods enhance the reliability of phase identification, their additional contribution may be considered limited compared to XRD in terms of cost-effectiveness. SEM analysis provides unique insights into the microstructural characteristics and heterogeneity of the material that cannot be obtained by other techniques and therefore entails a relatively higher labor requirement. Similarly, TGA offers valuable information on thermal behavior and phase decomposition, supporting the presence of carbonate phases. From a practical perspective, an optimal analytical sequence may begin with XRD and other fundamental techniques, followed by SEM for microstructural investigation. FTIR, Raman, and TGA analyses can be employed as complementary and confirmatory methods when necessary. In this context, although some techniques provide overlapping information, their combined use enhances the overall reliability of the results; however, in cases of limited resources, a simplified approach focusing on key techniques may still yield sufficiently robust outcomes. Nevertheless, it should be noted that the cost of such comprehensive analyses constitutes only a small fraction of the total budget in restoration and conservation-oriented construction projects. Therefore, considering the comprehensive and reliable data they provide, the combined use of these techniques is recommended. This approach enables accurate material characterization, thereby contributing to the selection of appropriate intervention strategies and improving long-term performance.

4.6. Physical Properties

The physical properties of the sandstone used in the building were determined experimentally. The physical properties of the S samples, taken from the collapsed sandstone in the building, are presented in

Table 1. Physical experiment results of sample S.

Sample	Unit Weight (g/cm3)	Specific Gravity	Compactness (%)	Porosity (%)	Water Absorption Rate (%)
S	2.40	2.58	93	7	1.93

. The bulk density of the S samples was measured as 2.40 g/cm³, the specific gravity as 2.58, the porosity as 7%, and the water absorption rate as 1.93%. These values were calculated as the averages of three different samples taken from the building.

4.7. Mechanical Properties

The compressive strength values of the sandstone samples taken from the collapsed sandstone of the Armenian Church, along with the average Schmidt hammer and UPV values from various locations in the building, are presented in

Table 2. Mechanical experiment results of sample S.

Sample	Schmidt Hammer (MPa)	UPV (m/s)	Poisson’s Ratio [77]	Compressive Strength (MPa)
S	5.51	1519.72	0.20	15.42

. The compressive strength, Schmidt hammer, and UPV values were determined experimentally, while Poisson’s ratio was obtained from the literature. Each compressive strength value was calculated as the average of three different samples. According to the compressive strength test, the S samples have a compressive strength of 15.42 MPa.

To determine the strength of the stone blocks from the Armenian Church, Schmidt hammer tests were applied to different areas of the building. To represent the entire structure, measurements were taken from solid blocks at various points on the east, north, south, and west facades, with 12, 12, 8, and 5 points, respectively. The Schmidt hammer results for the east, north, south, and west facades were measured as 5.65 MPa, 5.90 MPa, 5.83 MPa, and 4.65 MPa, respectively. The average of these values from all four facades is presented in Table 2. According to Molina et al. [77], relationships between the hardness, Poisson’s ratio, and Young’s modulus of different stones have been established. Considering the Schmidt hammer test results, a Poisson’s ratio of 0.2 was used for the stone samples.

UPV tests were conducted on different areas of the church to determine the ultrasonic pulse velocities of the stone blocks (Table 2). To represent the entire structure, measurements were taken from solid blocks at 5, 5, 6, and 4 different locations on the east, north, south, and west facades, respectively, and the averages were calculated. The UPV results from all stone blocks ranged between 1031 and 2339 m/s, with an average pulse velocity of 1519.72 m/s. The wide range observed in UPV results stems from the heterogeneous structure of the material under investigation. Historical building materials do not possess a homogeneous internal structure due to production techniques, the natural variability of raw materials, and the degradation processes they undergo over time. This variability is closely related to differences in porosity rate, microcrack density, void distribution, and mineralogical composition. Low UPV values generally indicate areas with higher porosity, the presence of microcracks, and effective decomposition processes; while high UPV values represent more compact areas with lower void ratios and less deteriorated regions. Therefore, the wide UPV range obtained can be considered an indicator of heterogeneity and different degrees of degradation within the material. This is a natural consequence of the varying physical and mechanical properties in different regions of the material, a common occurrence in historical structures.

The elastic moduli of the materials were calculated according to different regulations and standards, and the results are presented in

Table 3. Modulus of elasticity of sample S.

Sample	Modulus of Elasticity (GPa)
	Ed	E (DBYBHY)	E (FEMA 356)	E (TBDY)	E (Eurocode 6)
S	5.36	3.08	8.48	11.57	15.42

. For masonry elements, the Turkish Regulation on Buildings to be Built in Earthquake Zones (DBYBHY) recommends calculating the elastic modulus using the relationship E = 200f_c, where $f_c$ is the compressive strength. Additionally, the elastic modulus for wall materials is suggested to be calculated as E = 750f_c according to the Turkish Building Earthquake Code (TBDY), E = 550f_c according to FEMA 356, and E = 1000f_c according to Eurocode 6.

In addition, the dynamic elastic modulus (E_d) of the samples was determined according to the ASTM C597 standard. These values were calculated using Equation (6), which incorporates the ultrasonic pulse velocity, density, and Poisson’s ratio of the samples. In this equation, $V$ represents the ultrasonic pulse velocity, $\rho$ the density, and $\mu$ the Poisson’s ratio. Accordingly, the elastic modulus of the S sample was determined to be 5.36 GPa.

$${{\rm E}}_d={\displaystyle \frac{{\nu }^2\times \rho \times \left(1+\mu \right)\times \left(1-2\mu \right)}{\left(1-\mu \right)}}$$

(6)

The integrated evaluation of XRD, XRF, FTIR, Raman, SEM, and TGA analyses carried out within the scope of this study enables a comprehensive understanding of the relationships between the mineralogical, chemical, and microstructural properties of the material and its mechanical behavior. The identification of calcite as the dominant phase, along with quartz as a secondary phase and locally present dolomite in samples M and S, based on XRD, FTIR, and Raman analyses, is consistent with the high CaO content obtained from XRF results. This clearly indicates that the materials possess a lime-based binder system. The significant mass losses observed in TGA analyses, particularly within the temperature range of 600–900 °C, are associated with the decomposition of carbonate phases (especially calcite), which corroborates the carbonate minerals identified by XRD, FTIR, and Raman analyses. Additionally, the limited mass losses at lower temperatures indicate low moisture and clay content in the samples, which is consistent with the physical properties of the material. SEM analyses reveal the distribution of the mineral phases identified by other techniques within the microstructure and confirm the heterogeneous nature of the material. When these microstructural features are evaluated together with the porosity ratio (7%) and water absorption capacity (1.93%), they provide important insights into the physical integrity and internal structure of the material.

Considering all these findings collectively, it is understood that the calcite-based binder system imparts a certain level of strength to the material, while the microstructural characteristics and the distribution of components play a decisive role in determining mechanical performance. Indeed, the compressive strength of 15.42 MPa and ultrasonic pulse velocity of 1519.72 m/s determined for the S samples indicate that the material exhibits a moderate level of mechanical performance. This behavior can be explained through the combined evaluation of mineralogical structure, chemical composition, and microstructural properties.

In this context, it is recommended that future studies extend the present findings through integrated static and dynamic analyses, particularly under seismic loading conditions. Advanced approaches such as non-parametric fragility analysis, which do not rely on predefined distribution assumptions, could provide a more reliable assessment of damage evolution by incorporating the stochastic nature of ground motions and component-level responses. Such methodologies would enable a more accurate evaluation of the relationship between material properties and structural performance, thereby contributing to a more robust understanding of seismic resilience [78].

5. Conclusions and Recommendations

Within the scope of this study, the mineralogical, chemical, physical, and mechanical properties of the building materials used in the Old Armenian Church in Çanakkale were determined using multidisciplinary analysis methods. The results obtained are summarized as follows:

• XRD results indicated that calcite is the dominant mineral phase in the mortar and stone samples, with quartz also present in significant amounts in some samples. Additionally, dolomite, albite, gypsum, and hematite were detected. FTIR and Raman spectroscopy confirmed the presence of these mineral phases, while SEM images showed calcite-based binder matrices with quartz aggregates within the mortars. When the results obtained from XRD, FTIR, and Raman analyses are evaluated together, it is seen that the mineral phases determined in the samples show a high level of consistency. While XRD analyses constitute the basic reference method in the identification of crystalline phases, FTIR analyses support these phases with characteristic vibrational bands belonging to carbonate and silicate groups. Raman analyses, on the other hand, provide additional verification, especially in the identification of carbonate minerals. In the interpretation of spectral overlaps, multiple characteristic peaks were evaluated together instead of only individual bands, and the findings obtained were verified by comparing them among different analytical techniques. This multiple evaluation approach reduces uncertainties that may occur in phase identification and increases the reliability of the results.
• TGA results revealed low moisture and clay mineral content in the samples, whereas carbonate-based mineral phases were present in high amounts. Physical tests showed that the stone samples have a porosity of approximately 7% and a water absorption rate of 1.93%. Mechanical tests determined the compressive strength to be 15.42 MPa. UPV measurements indicated an average ultrasonic pulse velocity of 1519.72 m/s, and Schmidt hammer tests showed variable strength values across different facades. The dynamic elastic modulus, calculated according to ASTM C597, was 5.36 GPa.
• The results suggest that the carbonate-rich mineralogical structure and low porosity indicate a generally compact internal structure of the materials. However, relatively low ultrasonic velocities and variations in Schmidt hammer values across facades indicate that micro-cracks, weathering, or surface degradation may be present. This study demonstrates a direct relationship between the physical, chemical, and mineralogical properties of the building materials and environmental effects.
• Materials used in conservation and restoration should be compatible with the original building materials in terms of mineralogical and chemical composition. The analyses indicate that carbonate-based mineral phases dominate the building materials. Therefore, restoration mortars should preferably use air lime or natural hydraulic lime as binders. Quartz-based silica sand as aggregate in the mortars can help replicate the mineralogical and microstructural properties of the original mortars. For stone repairs, fine-crystalline, medium-porosity limestone with mineralogical and physical properties similar to the original stones is recommended. Samples containing dolomite suggest that dolomitic limestones can also be considered for restoration stones. Additionally, the physical properties of the replacement stones—such as density, porosity, water absorption, and mechanical strength—should closely match those of the existing stones.
• To achieve a more comprehensive assessment of the building’s structural behavior, the material properties obtained in this study can be used for numerical modeling and structural performance analyses. Finite Element Method (FEM)-based analyses, in particular, can evaluate the behavior of the structure under seismic and environmental loads, providing a reliable engineering basis for future conservation and restoration interventions.
• The analytical results indicate that carbonate-based mineralogical compositions are dominant in the building materials, highlighting the necessity for restoration materials to be compatible with the original structure in terms of mineralogical, physical, and mechanical properties. In this context, fine-crystalline and moderately porous limestones, along with dolomitic limestones, emerge as suitable alternatives. Furthermore, the identification of quartz within the carbonate matrix suggests that calcite-cemented sandstones may also be considered under appropriate conditions. Mechanical test results reveal that the examined stones are characterized by high porosity and low compressive strength. Therefore, the use of stones and mortars with higher strength and modulus of elasticity than the original materials may lead to mechanical incompatibilities. In particular, cement-based binding systems, due to their low vapor permeability and high rigidity, are likely to induce cracking, detachment, and surface deterioration. Physical and thermal analyses indicate low moisture and clay content, suggesting that the current deterioration processes are largely driven by environmental and atmospheric factors. Accordingly, it is recommended that restoration practices employ breathable lime-based mortars with high water vapor permeability, such as air lime, natural hydraulic lime, and pozzolan-enhanced lime mortars. As aggregates, silica sands or river sands with appropriate grain size distribution are recommended.
• In future studies, microcracks and surface degradation characteristics can be identified. Furthermore, measurements of, for example, moisture and salt content, which support environmental degradation mechanisms, can be performed, and the compatibility or performance of the proposed lime-based restoration materials can be verified through laboratory tests or simulations. Addressing these shortcomings in future studies is crucial for a more reliable assessment of degradation mechanisms and the validation of restoration works.
• To provide a more comprehensive assessment of the building’s structural behavior, the material properties obtained in this study can be used in numerical modeling and structural performance analysis. In particular, Finite Element Method (FEM)-based analyses can provide a reliable engineering basis for future conservation and restoration interventions by evaluating the building’s behavior under seismic and environmental loads. In addition, it is recommended that many more samples be taken and analyzed when deciding on the building’s restoration in the future.