Multidisciplinary characterisation, weathering patterns, and durability assessment of stone blocks for the conservation of Tamentfoust fort (ex. Rusguniae) in Algiers

The heritage represents the memory of the history and development of a country and should be preserved for new generations. The documentation and conservation of cultural heritage hold critical significance within scholarly and applied contexts. For stonework restoration projects, a rigorous understanding of construction materials and their intrinsic properties serves as an essential prerequisite for formulating effective intervention protocols [1]. Systematic evaluation of a monument's current state, particularly through analysis of the composition and conservation status of its constituent materials across historical periods, represents a central objective in heritage building investigations. Such analyses provide pivotal insights for modern restoration efforts, while facilitating the assessment of prior conservation interventions in terms of long-term efficacy and material compatibility [2]. This methodological necessity acquires heightened urgency in regions such as Algeria, where some twentieth-century conservation practices utilized before, incompatible and harmful materials in conservation practices, such as composite matrices to treat deteriorated stone in heritage structures. These treatments were frequently applied without a prior experimentation, disregarding physicochemical compatibility with historical substrates, thereby accelerating material degradation. Many experimental studies have clearly demonstrated, that ill-suited consolidants, including polysiloxane resins and epoxy polymers, induce detrimental interfacial stresses and chemical modifications in treated stone surfaces [3]. The deterioration of stone monuments, driven by environmental and atmospheric factors, presents a global conservation challenge. Weathering processes, encompassing physical disintegration and chemical decomposition, are governed by interactions between lithic substrates and exogenic agents, including climate, biogenic activity, and pollutants. Numerous studies have explored techniques for assessing stone decay, exemplified by Fitzner's classification of nineteen weathering forms, which enables systematic mapping of façade degradation. Such methodologies facilitate precise quantification of weathering extent and damage severity, which is critical for informed conservation.
Historic military architecture represents a critical facet of cultural heritage, often bearing testimony to the technological, strategic, and social conditions of its time. The Ottoman fort of Tamentfoust is one of the emblematic monuments of the military fortification system heritage site, in the city of Algiers. Its preservation and enhancement are vital for safeguarding cultural identity and ensuring the structure's long-term stability. This important part of Mediterranean cultural heritage is, unfortunately, progressively being degraded due to weathering problems, necessitating a comprehensive study and complete documentation of the monument to assess its status. The Tamentfoust fort, located on the Mediterranean coast, is in a deplorable state of conservation, largely due to several causes such as the use of Portland cement-based mortars in prior restoration efforts. These mortars, incompatible with traditional materials like stone and lime-based mortars, have
accelerated degradation by causing moisture accumulation, salt efflorescence, and cracking due to their rigidity and low vapor permeability effects, exacerbated by the saline marine environment. In stone buildings exposed to coastal conditions, cement mortars trap moisture and sea salts, leading to increased stone corrosion, joint disintegration, and loss of aesthetic authenticity. Research, such as that by Mahindad [4], demonstrates the efficacy of lime-based mortars combined with natural additives, such as olive oil and eggs, to enhance water repellency and reduce shrinkage. However, as it was noted in the same study that the documentation relating to the composition of old mortars in Algeria is not very rich, apart from some recent studies on the characterization of archaeological materials, which hinders long-term preservation efforts. Ouagueni in [5] advocates a shift toward locally sourced materials, such as natural hydraulic lime (NHL), later adopted in the restoration project of the citadel of Algiers and additives, like crushed bricks or vegetable fibers, to align with traditional construction techniques. This approach, supported by detailed physico-chemical analysis of historical mortars, ensures compatibility in terms of physical, chemical, and aesthetic properties while promoting sustainability through reduced environmental impact and the use of local resources. This paradigm shift underscores the urgent need for further research to develop repair mortars that respect the historical and cultural value of Algeria's built heritage, particularly for vulnerable structures like the Tamentfoust fort.
The scarcity of empirical data related to mechanical attributes and the precise architectural documentation of the construction materials, remains a recurring issue that also concerns the Tamentfoust fort. Therefore, through a multidisciplinary experimental investigation, the main purpose of the present study is to characterize the stone materials of the fort and to understand the degradation mechanisms affecting its external stone facades [6]. This integrated study was designed to inform conservation strategies with a robust scientific foundation, employing diagnostic techniques from geology, materials science, structural engineering, and conservation science [7]. The mineralogical and chemical composition of the stone materials was determined using X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF). Petrographic analysis using polarized light microscopy enabled the characterisation of textural features, mineral content, and alteration patterns. Micromorphological and compositional analyses were further conducted, using scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDX), facilitating high-resolution imaging of surface weathering phenomena. Physical and mechanical properties were quantified through measurements of apparent density and open porosity, as well as uniaxial compression and three-point bending tests to evaluate mechanical parameters. Water transport behaviour was assessed through capillary water absorption testing, which is an important indicator of stone vulnerability to moisture and associated decay processes. Durability was assessed by means of an accelerated aging test, which evaluates stone resistance to salt crystallization, one of the most destructive weathering mechanisms in porous materials. Non-destructive evaluations included ultrasonic pulse velocity testing, which offers insights into internal structural coherence, and infrared thermography to detect subsurface anomalies related to moisture and detachment [8]. Monitoring of structural stability was carried out through the measurement of micro-cracks in external walls and patio gallery columns. Additionally, a laser scanning survey was employed to generate a high-resolution geometric model of the fort's façades, supporting both documentation and deformation analysis. The methodological framework adopted in this study enables a comprehensive understanding of the material characteristics and degradation patterns of the Tamentfoust fort, offering a scientific basis for the development of targeted, effective, and sustainable conservation measures. The novelty of this research lies in its pioneering investigation of the Tamentfoust fort, marking the first study to comprehensively characterize the physical and mechanical properties of its natural stone materials in a coastal environment, a critical endeavor given the monument's significant historical and architectural value. This originality is further enhanced by the combined use of destructive and non-destructive testing techniques tailored to this specific material, integrated with Terrestrial Laser Scanning (TLS) technology, which provides comprehensive graphical documentation previously unavailable [9]. This multidisciplinary approach offers an optimized and rapid method for the characterization of heritage stone in engineering applications, setting a new standard for the preservation and study of similar historical structures.

Tamentfoust, a key site for historical and architectural research, embodies a rich cultural evolution reflected in its changing names. Known as Rusguniae during Roman times, a name derived from the Phoenician "Rus"(meaning a bushy promontory) [10], it became Tamentfoust, meaning "hand" in the Tamazight language, during the BerberOttoman period. By the 14th century, Spanish influence renamed it Cap Matifou, and later, French colonial rule designated it Laperouse. Located 20 km east of Algiers along the eastern shore of the Bay of Algiers (Fig. 1), the city of Tamentfoust's defensive significance is evidenced by a network of fortifications, including Fort L'Empreur on the west coast of the bay of Algiers, and the Ottoman-era fort of Tamentfoust on the eastern side of the same bay [11]. Historical records confirm Rusguniae was founded as a Roman colony by Augustus in 30 Before Common Era (BCE), later thriving as a Byzantine urban center [10]; [11]. Its orthogonal urban layout, covering 19 hectares, included two gateways (Fig. 2), with a north-eastern portal connecting to the Icosium-Tipasa trade route.
The 7th-century Arab conquest brought significant socio-religious changes. In the 12th century, the geographer Al-Idrīsī described Tamentfoust as "[...] a picturesque harbor beside ruins, with traces of temples and stone idols [...]"[10].A quarry, linked underground to Rusguniae's port, provided stone for Algiers' fortifications. Modern urban expansion has since obscured much of the site's archaeological remains, highlighting the urgent need for heritage preservation. The construction history of Tamentfoust's Ottoman fort is debated. Henri Klein dates its initial construction to 1661 under Ramadhan Agha, with further fortifications added after a 1685 bombardment [11]. In contrast, Georges Marçais argues for a 1722 foundation, citing French destruction in 1685 and subsequent rebuilding. This fort, strategically vital, anchored Algiers' defences at the eastern edge of the bay of Algiers. Salama in [11] identifies it as a model Ottoman coastal defence structure, built over Roman ruins (Rusguniae) to counter Spanish incursions and secure Mediterranean trade routes. Ottoman records highlight its importance during Khayr al-Din Barbarossa’s rule. Al-Idrīsīs 12th-century account further
notes Tamentfoust as "[...] a port nears a ruined settlement, preserving ancient relics [...]"[10]. After Ottoman revitalization, the site declined from the 18th century due to harbour siltation and Algiers' growing dominance.
The fort's architecture reflects a succession of cultural influences. Latin-inscribed spolia were incorporated into Ottoman masonry, while semi-circular bastions show Iberian design elements. Nineteenth-century excavations uncovered Ottoman ceramics alongside Roman column bases, providing evidence of continuous occupation. Despite 19th-century urban encroachment, the Cap Matifou ramparts endure as a testament to their military past, though locals have historically reused their stones.
Declared a national heritage site in 1967, the fort was converted into a museum in 1999. However, nearby urban development continues to threaten its preservation.

The Ottoman fort of Tamentfoust is located at ${36}^{\circ }{48}^{\prime }{23}^{\prime \prime }\mathrm{N},3^{\circ }{13}^{\prime }{50}^{\prime \prime }\mathrm{E}$${36}^{\circ }{48}^{\prime }{23}^{\prime \prime }\mathrm{N},3^{\circ }{13}^{\prime }{50}^{\prime \prime }\mathrm{E}$36^(@)48^(')23^('')N,3^(@)13^(')50^('')E36^{\circ} 48^{\prime} 23^{\prime \prime} \mathrm{N}, 3^{\circ} 13^{\prime} 50^{\prime \prime} \mathrm{E}${36}^{\circ }{48}^{\prime }{23}^{\prime \prime }\mathrm{N},3^{\circ }{13}^{\prime }{50}^{\prime \prime }\mathrm{E}$, approximately 25 km east of Algiers. It is bordered primarily by the El Marsa massif to the north and east, and by the Mediterranean Sea to the south and west. The meteorological data including temperature, rainfall, humidity rate and wind speed, were obtained from the Algerian National Meteorological Office for the period 2006-2020 .These data were statistically analysed to identify monthly trends in temperature and precipitation, presented in two graphs, to highlight relationships between variables and distinguish dry and wet periods in the Bay of Algiers, (Cf. Appendix A1).
Strategically located at the eastern edge of Algiers Bay, the fort of Tamentfoust, exemplifies a distinctive architectural paradigm, within North Africa's defensive networks. Unlike typical Ottoman designs of the period, its octagonal morphology ( 28 m diameter base) with a 3 -meter-deep perimeter moat reflects advanced tactical engineering, enabling enhanced defender mobility and encirclement strategies. Access is provided through a southeastern drawbridge ( $5\times 1.5$$5\times 1.5$5xx1.55 \times 1.5$5\times 1.5$ m) leading to a postern gate. The 9 -meter-high walls with a pronounced batter incorporate covered median and corner towers, equipped with arrow slits and loopholes. An upper terrace, with a parapet walkway, overlooks an arcaded central courtyard, which houses functional spaces (kitchen, prayer hall, prison, hammam, and armory), accessible via a lateral staircase (Fig. 2). The 1992 restoration campaign identified multiple forms of deterioration, including: exfoliation, fissures, fractures, alveolar erosion, stone detachment, delamination, and rain-induced deposits, particularly in areas exposed to meteorological stressors such as solar radiation, saline aerosols, and humidity. Subsequent interventions in 2012 used cement-based mortars for façade repointing, a method criticized for its incompatibility with the fort's historical stone substrates.

The stone deterioration mechanisms at Tamentfoust fort, are closely tied to the region's geological and structural context. The Algerian continental margin, part of the southern Mediterranean basin, is integrated into the internal domain of the Tellian Atlas chain [12]. Paleoanthropological investigations identify Ain Taya, located 6 km
southwest of Tamentfoust's urban core, as a principal lithic source. Piroutet describes two stratigraphic horizons overlying Cartennien marls and Pliocene sands: a lower red sand stratum yielding Mousterian quartzite tools, and an upper greyish sand stratum, containing Neolithic flint artefacts. Piroutet further attributes the Roman-era quarrying of Tamentfoust's construction stones to Ain Taya. The Tertiary Miocene sequence, exposed eastward between Cap El Marsa and Bordj el Bahri, consists of Burdigalian marls with sandstone lenses and Vindobonian marly limestone's. Tectonic activity during this period, included Lower Miocene uplift of the Atlas range, and formation of the Mitidja-Cheliff synclinorium, followed by Middle Miocene extensional tectonics, volcanism, and the emergence of the Mitidja basin.

Four stone blocks (E1, E3) as type T1 and (E2, E4) as type T2 with dimensions approximately of $17\times 37\times 15\mathrm{cm}$$17\times 37\times 15\mathrm{cm}$17 xx37 xx15cm17 \times 37 \times 15 \mathrm{~cm}$17\times 37\times 15\mathrm{cm}$, collected from the immediate surroundings of the fort, belong to the damaged masonry wall on the fort's terrace (Fig. 3). The blocks were cut into parallelepipedical specimens $30\times 5\times 5\mathrm{cm}$$30\times 5\times 5\mathrm{cm}$30 xx5xx5cm30 \times 5 \times 5 \mathrm{~cm}$30\times 5\times 5\mathrm{cm}$, and cylindrical specimens via core drilling 50 mm bit (Fig. 5), (Fig. 6). For microscopic studies, thin sections were also prepared from the two blocks (Fig. 4). Stone samples were selected for their historical texture, avoiding contemporary materials to focus on the early construction phase, due to monument restorations in the 1992s and 2012. Below, are listed all the tests carried out, summarized in Tab. 1, with reference to the tested specimens.

$\mathbf{D}=$$\mathbf{D}=$D=\mathbf{D}=$\mathbf{D}=$ density, $\mathbf{C}\mathbf{a}=$$\mathbf{C}\mathbf{a}=$Ca=\mathbf{C a}=$\mathbf{C}\mathbf{a}=$ capillarity, $\mathbf{P}\mathbf{o}=$$\mathbf{P}\mathbf{o}=$Po=\mathbf{P o}=$\mathbf{P}\mathbf{o}=$ porosity, $\mathbf{U}\mathbf{C}\mathbf{S}=$$\mathbf{U}\mathbf{C}\mathbf{S}=$UCS=\mathbf{U C S}=$\mathbf{U}\mathbf{C}\mathbf{S}=$ Uniaxial compressive strength, $\mathbf{U}\mathbf{W}\mathbf{V}=$$\mathbf{U}\mathbf{W}\mathbf{V}=$UWV=\mathbf{U W V}=$\mathbf{U}\mathbf{W}\mathbf{V}=$ Ultrasonic wave velocity, $\mathbf{W}\mathbf{A}=$$\mathbf{W}\mathbf{A}=$WA=\mathbf{W A}=$\mathbf{W}\mathbf{A}=$ water absorption, Petr= Petrography, Du-Cryst= Durability test by salt crystallization, Du-Acd= Durability with accelerated ageing with HCl , XRD=X-ray diffraction, XRF= X-ray fluorescence, SEM-EDX=Scanning Electron Microscopy, Cra= Micro-cracks measurement, $\mathbf{S}\mathbf{H}\mathbf{R}=$$\mathbf{S}\mathbf{H}\mathbf{R}=$SHR=\mathbf{S H R}=$\mathbf{S}\mathbf{H}\mathbf{R}=$ Schmidt hammer rebound, $\mathbf{F}\mathbf{S}\mathbf{T}=$$\mathbf{F}\mathbf{S}\mathbf{T}=$FST=\mathbf{F S T}=$\mathbf{F}\mathbf{S}\mathbf{T}=$ Flexural strength test, $\mathbf{M}\mathbf{p}\mathbf{a}\mathbf{l}=$$\mathbf{M}\mathbf{p}\mathbf{a}\mathbf{l}=$Mpal=\mathbf{M p a l}=$\mathbf{M}\mathbf{p}\mathbf{a}\mathbf{l}=$ Micropaleontological study

Table 1: Samples description and the relative tests.

E2 Micrite with bioclasts Foraminifera: The age of this sample is

Petrographical examination revealed that the stone sample PE1-5 T1 was a white to beige sedimentary rock with a massive structure and grainstone texture, according to Dunham's classification. It is a fossiliferous limestone composed mainly of carbonate cement containing fossiliferous and detrital material (Fig. 7a, photomicrograph of thin section 01 showing plagioclase, quartz, microcline, and biotite under cross-polarized light at 6.3 x magnification). The light-coloured cement is formed by microsparite calcite with an average size of 0.05 mm , occupying around $50\mathrm{\%}$$50\mathrm{\%}$50%50 \%$50\mathrm{\%}$ of the total volume of the rock (Fig. 7b, photomicrograph of thin section 01 showing fossils and quartz under cross- polarized light at 6.3 x magnification). The rock is characterized by the presence of fossils of various shapes and sizes ranging from 0.05 to 0.6 mm , with tests that are generally whole to occasionally fragmented. Some fossils are recrystallized by secondary calcite. Detrital material is represented by disseminated quartz grains, angular in shape and varying in size from 0.05 to 0.5 mm (Fig. 7c, photomicrograph of thin section 01 showing muscovite under cross-polarized light at 6.3 x magnification). The feldspars are represented by elongated plagioclases varying in size from 0.05 to 0.1 mm . The microcline is also distinguished by its squared-off macles. Biotite is rarely seen, in the form of lamellae averaging 0.3 mm in size. Muscovite appears as fine rods, ranging in size from 0.05 to 0.2 mm . Opaque minerals are poorly represented, showing isolated grains of automorphic form and ranging in size from 0.05 to 0.1 mm . Porosity is marked by the presence of voids sometimes recrystallized by secondary calcite Tab. 3.
For the sample ${\mathrm{PE}}_2-6$${\mathrm{PE}}_2-6$PE_(2)-6\mathrm{PE}_{2}-6${\mathrm{PE}}_2-6$ (T2) the petrographic study summarised in Tab. 4, shows that it's a fossiliferous limestone with a massive structure and grainstone texture (Fig. 8a, photomicrograph of thin section 04 showing fossils and quartz under cross-polarized light at $6.3x$$6.3x$6.3 x6.3 x$6.3x$ magnification). It is composed mainly of carbonate cement containing fossils, as well as feldspar, quartz, chlorite and muscovite (Fig. 8b), photomicrograph of thin section 04 showing fossils under cross-
polarized light at 6.3 x magnification). The cement covers around $40\mathrm{\%}$$40\mathrm{\%}$40%40 \%$40\mathrm{\%}$ of the total volume of the rock and takes the form of a microspartic composed of calcite averaging 0.05 mm in size (Fig. 8c), photomicrograph of thin section 04 showing Muscovite under cross-polarized light at 10x magnification).

Fossils are widespread in the rock, showing various forms of nummulites, radiolarians, orbitolites, etc. with whole or sometimes fragmented tests filled with secondary calcite, up to 1 mm in size. Feldspars are represented by plagioclases in the form of small elongated patches showing clearly visible polysynthetic macles with an average size of 0.2 mm , noting the presence of the elongated perthitic orthoclase and the very common microcline, clearly distinguished with its squared macle. Quartz occurs in angular grains ranging in size from 0.05 to 0.5 mm .
There are a few quartz clasts, which are generally polycrystalline, represented by crystals that are well interlocked with one another and up to 3 mm in size. Fine chlorite lamellae are observed, with a greenish colour and a size that varies from 0.05 to 0.2 mm . Muscovite occurs in the form of rods averaging 0.4 mm in size. The opaque minerals show small isolated grains of automorphic shape and 0.05 to 0.1 mm in size (Fig. 8d, photomicrographs of thin section 04 showing fossils, quartz, plagioclase, and chlorite under cross-polarized light and plane-polarized light at 10 x magnification). The rock has a few notable voids and microcracks, reflecting its porosity.

The fort stone sample PE1-3 subjected to crystallisation test, a light-colored fossiliferous limestone with a massive grainstone structure, consists of $50\mathrm{\%}$$50\mathrm{\%}$50%50 \%$50\mathrm{\%}$ microsparite calcite cement ( $<0.1\mathrm{mm}$$<0.1\mathrm{mm}$< 0.1mm<0.1 \mathrm{~mm}$<0.1\mathrm{mm}$ ), $30\mathrm{\%}$$30\mathrm{\%}$30%30 \%$30\mathrm{\%}$ fossils (up to 0.6 mm , various shapes), quartz ( $0.05-0.5\mathrm{mm}$$0.05-0.5\mathrm{mm}$0.05-0.5mm0.05-0.5 \mathrm{~mm}$0.05-0.5\mathrm{mm}$, angular), elongated plagioclases ( 0.1 mm ), xenomorphic microcline ( 0.1 mm , grid-pattern macles), micas (biotite lamellae $0.1-0.4\mathrm{mm}$$0.1-0.4\mathrm{mm}$0.1-0.4mm0.1-0.4 \mathrm{~mm}$0.1-0.4\mathrm{mm}$, muscovite 0.2 mm ), rare automorphic opaque minerals ( $0.05-0.1\mathrm{mm}$$0.05-0.1\mathrm{mm}$0.05-0.1mm0.05-0.1 \mathrm{~mm}$0.05-0.1\mathrm{mm}$ ), and reddish iron hydroxide coatings Tab. 5, (Fig. 9). Calcite dissolution by ${\mathrm{Cl}}^{-}$${\mathrm{Cl}}^{-}$Cl^(-)\mathrm{Cl}^{-}${\mathrm{Cl}}^{-}$ions weakens the cement, reducing matrix cohesion, resulting in a modest mass loss ( $\mathrm{\Delta }\mathrm{M}:0.65\mathrm{\%}$$\mathrm{\Delta }\mathrm{M}:0.65\mathrm{\%}$DeltaM:0.65%\Delta \mathrm{M}: 0.65 \%$\mathrm{\Delta }\mathrm{M}:0.65\mathrm{\%}$ ) and a compressive strength ( ${\sigma }_{\mathrm{c}}$${\sigma }_{\mathrm{c}}$sigma_(c)\sigma_{\mathrm{c}}${\sigma }_{\mathrm{c}}$ ) reduction of $<10\mathrm{\%}$$<10\mathrm{\%}$< 10%<10 \%$<10\mathrm{\%}$, indicating minimal surface degradation. Moderate porosity, inferred from 1% iron hydroxides and EDX-detected oxygen content pores ( 70.20 atom $\mathrm{\%}$$\mathrm{\%}$%\%$\mathrm{\%}$ ), may amplify cyclic damage under salt-induced stress. However, partial pore obstruction by hydroxides limits connectivity, mitigating strength loss. The heterogeneous microstructure, with microfossils and cement as primary crack initiation sites, increases susceptibility to cyclic deterioration due to porosity and mineral variability.

Petrographic analysis after ageing test with HCl , of the T2-type stone sample PE2-4 summarised in Tab. 6 revealed a sedimentary rock with a massive structure and grainstone texture. It is a fossiliferous limestone, consisting of a carbonate matrix containing abundant fossiliferous material. The cement has a light background and is formed by microsparite calcite with an average size of 0.05 mm (Fig. 10). Calcite occupies approximately $50\mathrm{\%}$$50\mathrm{\%}$50%50 \%$50\mathrm{\%}$ of the total rock volume. Fossils are relatively abundant, in various forms (Nummulites, Orbitolites, etc.), up to 1.5 mm in size. These fossils have intact tests and are recrystallized by secondary calcite. The detrital material contains quartz, sometimes disseminated in angular form, ranging in size from 0.05 to 0.1 mm . Disseminated plagioclase is elongated and averages 0.2 mm in size. Microcline is present in a grid pattern, 0.1 mm in size. Muscovite rods are observed, varying in size from 0.05 to 0.4 mm . Opaque minerals are automorphic and vary in size from 0.05 to 0.1 mm . Iron hydroxides appear as a reddish coating. The rock is characterized by voids that are rarely recrystallized by secondary calcite. Post-test petrography revealed etched calcite grains, increased porosity, and potential microcracking. XRD analysis revealed reduced calcite peaks and increased amorphous phases due to dissolution processes (Fig. 11). Quartz and silicate peaks remain stable, while XRF and EDX
analyses, reported in Tab. 8 and Tab. 12, respectively, showed a decrease in calcium content and an increase in chlorine, attributed to HCl reaction products, with stable silicon and other silicate-related elements, confirming the stone's chemical alteration under acidic conditions. The predominant chemical process involves the dissolution of carbonate minerals. The interaction of HCl with stone is primarily attributed to chemical reactions between this atmospheric pollutant and calcium-bearing minerals within the stone matrix, such as calcite, dolomite, plagioclase, and actinolite. Even in stones with minimal or no intrinsic calcium content, calcium ions may originate from exogenous sources, including adjacent limebased mortars, calcareous building materials, or atmospheric particulate deposition.

XRF, XRD, and EDX were used to characterize stone samples PE1-5 (T1) and PE2-6 (T2) from Tamentfoust fort, revealing a carbonate-silicate composition with potential metamorphic or igneous origins [21]. XRF analysis identified major and trace elements, including calcium ( $23.53-25.00\mathrm{\%}$$23.53-25.00\mathrm{\%}$23.53-25.00%23.53-25.00 \%$23.53-25.00\mathrm{\%}$ ), silicon ( $5.85-6.32\mathrm{\%}$$5.85-6.32\mathrm{\%}$5.85-6.32%5.85-6.32 \%$5.85-6.32\mathrm{\%}$ ), iron ( $0.808\mathrm{\%}$$0.808\mathrm{\%}$0.808%0.808 \%$0.808\mathrm{\%}$ ), and manganese ( $0.015\mathrm{\%}$$0.015\mathrm{\%}$0.015%0.015 \%$0.015\mathrm{\%}$ ) Tab. 7. XRD analysis detected crystalline phases, such as dolomite ( $\mathrm{CaMg}{\left({\mathrm{CO}}_3\right)}_2$$\mathrm{CaMg}{\left({\mathrm{CO}}_3\right)}_2$CaMg(CO_(3))_(2)\mathrm{CaMg}\left(\mathrm{CO}_{3}\right)_{2}$\mathrm{CaMg}{\left({\mathrm{CO}}_3\right)}_2$ ), quartz ( ${\mathrm{SiO}}_2$${\mathrm{SiO}}_2$SiO_(2)\mathrm{SiO}_{2}${\mathrm{SiO}}_2$ ), pyroxene ( $(\mathrm{Mg},\mathrm{Fe}){\mathrm{SiO}}_3)$$\left.(\mathrm{Mg},\mathrm{Fe}){\mathrm{SiO}}_3\right)${:(Mg,Fe)SiO_(3))\left.(\mathrm{Mg}, \mathrm{Fe}) \mathrm{SiO}_{3}\right)$(\mathrm{Mg},\mathrm{Fe}){\mathrm{SiO}}_3)$, muscovite, cristobalite, and sylvanite, with $\mathrm{PE}2-6$$\mathrm{PE}2-6$PE2-6\mathrm{PE} 2-6$\mathrm{PE}2-6$ showing similar mineralogy but with magnesium-calcium carbonate versus magnesian calcite in PE1-5 (Fig. 11). EDX analysis Tab. 9, confirmed higher surface calcium (34.51$35.49\mathrm{\%}$$35.49\mathrm{\%}$35.49%35.49 \%$35.49\mathrm{\%}$ ) and silicon ( $9.36-10.67\mathrm{\%}$$9.36-10.67\mathrm{\%}$9.36-10.67%9.36-10.67 \%$9.36-10.67\mathrm{\%}$ ), validating XRF results, and indicated micro-inhomogeneities, low heavy metal contamination (copper, zinc, lead), and high oxygen content ( $54.82\mathrm{\%}$$54.82\mathrm{\%}$54.82%54.82 \%$54.82\mathrm{\%}$ ), supporting carbonate-silicate structures . Sample PE2-6 exhibited slightly higher calcium and aluminum, plus titanium (absent in PE1-5) and elevated manganese, while PE1-5 had marginally more silicon; iron content remained comparable. Trace elements, such as sulfur, showed minor variations. Low toxic element levels (lead, arsenic) ensure safety for applications, particularly for PE2-6. With calcite content below $40\mathrm{\%}$$40\mathrm{\%}$40%40 \%$40\mathrm{\%}$ (Tab. 10, Fig. 12), ISRM standards indicate that no consolidation treatments are required.
After the salt crystallisation test, the elevated oxygen content ( $50.50\mathrm{wt}\mathrm{\%}$$50.50\mathrm{wt}\mathrm{\%}$50.50wt%50.50 \mathrm{wt} \%$50.50\mathrm{wt}\mathrm{\%}$ ) was recorded on the T1 litotype sample PE1-3. This result indicates the dominance of oxygen-rich minerals, such as silicates and carbonates, which may increase porosity and chemical susceptibility to NaCl crystallization damage. Chemical processes involve NaCl dissolution in water: $\mathrm{NaCl}(\mathrm{s})\to {\mathrm{Na}}^{+}(\mathrm{aq})+{\mathrm{Cl}}^{-}(\mathrm{aq})$$\mathrm{NaCl}(\mathrm{s})\to {\mathrm{Na}}^{+}(\mathrm{aq})+{\mathrm{Cl}}^{-}(\mathrm{aq})$NaCl(s)rarrNa^(+)(aq)+Cl^(-)(aq)\mathrm{NaCl}(\mathrm{s}) \rightarrow \mathrm{Na}^{+}(\mathrm{aq})+\mathrm{Cl}^{-}(\mathrm{aq})$\mathrm{NaCl}(\mathrm{s})\to {\mathrm{Na}}^{+}(\mathrm{aq})+{\mathrm{Cl}}^{-}(\mathrm{aq})$. This is followed by recrystallization upon evaporation, where ${\mathrm{Na}}^{+}$${\mathrm{Na}}^{+}$Na^(+)\mathrm{Na}^{+}${\mathrm{Na}}^{+}$and ${\mathrm{Cl}}^{-}$${\mathrm{Cl}}^{-}$Cl^(-)\mathrm{Cl}^{-}${\mathrm{Cl}}^{-}$recombine into NaCl crystals within pores, generating internal pressure and mechanical damage. Additionally, under humid conditions with ${\mathrm{CO}}_2$${\mathrm{CO}}_2$CO_(2)\mathrm{CO}_{2}${\mathrm{CO}}_2$, carbonate interactions occur: ${\mathrm{CaCO}}_3(\mathrm{s})+2\mathrm{NaCl}(\mathrm{aq})+{\mathrm{CO}}_2(\mathrm{g})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})\to {\mathrm{CaCl}}_2(\mathrm{aq})+2{\mathrm{NaHCO}}_3(\mathrm{aq})$${\mathrm{CaCO}}_3(\mathrm{s})+2\mathrm{NaCl}(\mathrm{aq})+{\mathrm{CO}}_2(\mathrm{g})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})\to {\mathrm{CaCl}}_2(\mathrm{aq})+2{\mathrm{NaHCO}}_3(\mathrm{aq})$CaCO_(3)(s)+2NaCl(aq)+CO_(2)(g)+H_(2)O(l)rarrCaCl_(2)(aq)+2NaHCO_(3)(aq)\mathrm{CaCO}_{3}(\mathrm{~s})+2 \mathrm{NaCl}(\mathrm{aq})+\mathrm{CO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{aq})+2 \mathrm{NaHCO}_{3}(\mathrm{aq})${\mathrm{CaCO}}_3(\mathrm{s})+2\mathrm{NaCl}(\mathrm{aq})+{\mathrm{CO}}_2(\mathrm{g})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})\to {\mathrm{CaCl}}_2(\mathrm{aq})+2{\mathrm{NaHCO}}_3(\mathrm{aq})$.
The T2 lithotype sample PE2-4, a calcite-dominated limestone with fossil inclusions, exhibits significant reactivity to hydrochloric acid ( HCl ), evidenced by ${\mathrm{CO}}_2$${\mathrm{CO}}_2$CO_(2)\mathrm{CO}_{2}${\mathrm{CO}}_2$ liberation. Silicate minerals (quartz, feldspars, and micas) show robust resistance to acidic and aqueous degradation but undergo protracted clay-phase alteration. Opaque phases and ferric hydroxides, such as pyrite ( ${\mathrm{FeS}}_2$${\mathrm{FeS}}_2$FeS_(2)\mathrm{FeS}_{2}${\mathrm{FeS}}_2$ ) and goethite ( $\mathrm{FeO}(\mathrm{OH})$$\mathrm{FeO}(\mathrm{OH})$FeO(OH)\mathrm{FeO}(\mathrm{OH})$\mathrm{FeO}(\mathrm{OH})$ ), demonstrate minimal acid reactivity, though oxidative transformation occurs in hydrated, oxygenated systems. Pyrite reacts with HCl to produce ${\mathrm{FeCl}}_2$${\mathrm{FeCl}}_2$FeCl_(2)\mathrm{FeCl}_{2}${\mathrm{FeCl}}_2$ and toxic ${\mathrm{H}}_2\mathrm{S}$${\mathrm{H}}_2\mathrm{S}$H_(2)S\mathrm{H}_{2} \mathrm{~S}${\mathrm{H}}_2\mathrm{S}$ gas via: ${\mathrm{FeS}}_2(\mathrm{s})+2\mathrm{HCl}(\mathrm{aq})\to {\mathrm{FeCl}}_2(\mathrm{aq})+{\mathrm{H}}_2\mathrm{S}(\mathrm{g})$${\mathrm{FeS}}_2(\mathrm{s})+2\mathrm{HCl}(\mathrm{aq})\to {\mathrm{FeCl}}_2(\mathrm{aq})+{\mathrm{H}}_2\mathrm{S}(\mathrm{g})$FeS_(2)(s)+2HCl(aq)rarrFeCl_(2)(aq)+H_(2)S(g)\mathrm{FeS}_{2}(\mathrm{~s})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{FeCl}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{~S}(\mathrm{~g})${\mathrm{FeS}}_2(\mathrm{s})+2\mathrm{HCl}(\mathrm{aq})\to {\mathrm{FeCl}}_2(\mathrm{aq})+{\mathrm{H}}_2\mathrm{S}(\mathrm{g})$. Ferric hydroxides (e.g., goethite) dissolve under HCl exposure:
$\mathrm{FeO}(\mathrm{OH})(\mathrm{s})+3\mathrm{HCl}(\mathrm{aq})\to {\mathrm{FeCl}}_3(\mathrm{aq})+2{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$$\mathrm{FeO}(\mathrm{OH})(\mathrm{s})+3\mathrm{HCl}(\mathrm{aq})\to {\mathrm{FeCl}}_3(\mathrm{aq})+2{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$FeO(OH)(s)+3HCl(aq)rarrFeCl_(3)(aq)+2H_(2)O(l)\mathrm{FeO}(\mathrm{OH})(\mathrm{s})+3 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{FeCl}_{3}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})$\mathrm{FeO}(\mathrm{OH})(\mathrm{s})+3\mathrm{HCl}(\mathrm{aq})\to {\mathrm{FeCl}}_3(\mathrm{aq})+2{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$. Calcite reacts vigorously with HCl , generating ${\mathrm{CO}}_2,{\mathrm{H}}_2\mathrm{O}$${\mathrm{CO}}_2,{\mathrm{H}}_2\mathrm{O}$CO_(2),H_(2)O\mathrm{CO}_{2}, \mathrm{H}_{2} \mathrm{O}${\mathrm{CO}}_2,{\mathrm{H}}_2\mathrm{O}$, and soluble ${\mathrm{CaCl}}_2:{\mathrm{CaCO}}_3(\mathrm{s})+2\mathrm{HCl}(\mathrm{aq})\to {\mathrm{CaCl}}_2(\mathrm{aq})+{\mathrm{CO}}_2(\mathrm{g})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$${\mathrm{CaCl}}_2:{\mathrm{CaCO}}_3(\mathrm{s})+2\mathrm{HCl}(\mathrm{aq})\to {\mathrm{CaCl}}_2(\mathrm{aq})+{\mathrm{CO}}_2(\mathrm{g})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$CaCl_(2):CaCO_(3)(s)+2HCl(aq)rarrCaCl_(2)(aq)+CO_(2)(g)+H_(2)O(l)\mathrm{CaCl}_{2}: \mathrm{CaCO}_{3}(\mathrm{~s})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{aq})+\mathrm{CO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})${\mathrm{CaCl}}_2:{\mathrm{CaCO}}_3(\mathrm{s})+2\mathrm{HCl}(\mathrm{aq})\to {\mathrm{CaCl}}_2(\mathrm{aq})+{\mathrm{CO}}_2(\mathrm{g})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$. Hydrolytic feldspar degradation contrasts sharply with quartz, which exhibits negligible dissolution kinetics in acidic, calcium-rich environments. Primary silicates (feldspars, micas, chlorites) are susceptible to gaseous HCl in hydrated conditions, with plagioclases ( ${\mathrm{NaAlSi}}_3{\mathrm{O}}_8-{\mathrm{CaAl}}_2{\mathrm{Si}}_2{\mathrm{O}}_8$${\mathrm{NaAlSi}}_3{\mathrm{O}}_8-{\mathrm{CaAl}}_2{\mathrm{Si}}_2{\mathrm{O}}_8$NaAlSi_(3)O_(8)-CaAl_(2)Si_(2)O_(8)\mathrm{NaAlSi}_{3} \mathrm{O}_{8}-\mathrm{CaAl}_{2} \mathrm{Si}_{2} \mathrm{O}_{8}${\mathrm{NaAlSi}}_3{\mathrm{O}}_8-{\mathrm{CaAl}}_2{\mathrm{Si}}_2{\mathrm{O}}_8$ ) releasing cationic species $({\mathrm{Ca}}^{2+},{\mathrm{K}}^{+},{\mathrm{Na}}^{+},{\mathrm{Mg}}^{2+},{\mathrm{Fe}}^{2+}/{}^{3+})$$\left({\mathrm{Ca}}^{2+},{\mathrm{K}}^{+},{\mathrm{Na}}^{+},{\mathrm{Mg}}^{2+},{\mathrm{Fe}}^{2+}/{}^{3+}\right)$(Ca^(2+),K^(+),Na^(+),Mg^(2+),Fe^(2+)//^(3+))\left(\mathrm{Ca}^{2+}, \mathrm{K}^{+}, \mathrm{Na}^{+}, \mathrm{Mg}^{2+}, \mathrm{Fe}^{2+} /{ }^{3+}\right)$({\mathrm{Ca}}^{2+},{\mathrm{K}}^{+},{\mathrm{Na}}^{+},{\mathrm{Mg}}^{2+},{\mathrm{Fe}}^{2+}/{}^{3+})$ under $\mathrm{HCl}-$$\mathrm{HCl}-$HCl-\mathrm{HCl}-$\mathrm{HCl}-$ polluted humidity, forming soluble derivatives. Acidic hydrolysis of feldspars yields secondary kaolinite-dominated clay matrices, underscoring the interplay between mineralogy, atmospheric pollutants, and long-term lithological alteration. This reaction can be expressed as:

Superficial alteration, involving water and ${\mathrm{CO}}_2$${\mathrm{CO}}_2$CO_(2)\mathrm{CO}_{2}${\mathrm{CO}}_2$, results in transformation into clays (e.g., kaolinite), affecting minerals such as microcline ( ${\mathrm{KAlSi}}_3{\mathrm{O}}_8$${\mathrm{KAlSi}}_3{\mathrm{O}}_8$KAlSi_(3)O_(8)\mathrm{KAlSi}_{3} \mathrm{O}_{8}${\mathrm{KAlSi}}_3{\mathrm{O}}_8$ ), orthoclase ( ${\mathrm{KAlSi}}_3{\mathrm{O}}_8$${\mathrm{KAlSi}}_3{\mathrm{O}}_8$KAlSi_(3)O_(8)\mathrm{KAlSi}_{3} \mathrm{O}_{8}${\mathrm{KAlSi}}_3{\mathrm{O}}_8$ ), and muscovite ( ${\mathrm{KAl}}_2\left({\mathrm{AlSi}}_3{\mathrm{O}}_{10}\right)(\mathrm{OH}{)}_2$${\mathrm{KAl}}_2\left({\mathrm{AlSi}}_3{\mathrm{O}}_{10}\right)(\mathrm{OH}{)}_2$KAl_(2)(AlSi_(3)O_(10))(OH)_(2)\mathrm{KAl}_{2}\left(\mathrm{AlSi}_{3} \mathrm{O}_{10}\right)(\mathrm{OH})_{2}${\mathrm{KAl}}_2\left({\mathrm{AlSi}}_3{\mathrm{O}}_{10}\right)(\mathrm{OH}{)}_2$ ). The stone, composed of $40\mathrm{\%}$$40\mathrm{\%}$40%40 \%$40\mathrm{\%}$ calcite, $35\mathrm{\%}$$35\mathrm{\%}$35%35 \%$35\mathrm{\%}$ fossils, $15\mathrm{\%}$$15\mathrm{\%}$15%15 \%$15\mathrm{\%}$ quartz, and minor silicates, showed calcite dissolution ( 0.05 mm grains) causing grain detachment and structural instability, while quartz and silicates (angular or elongated) remained largely unreactive Tab. 6.
Fossil morphology increased localized porosity (po: 8.59%), with SEM revealing cavities and pores ( $30-50\mu \mathrm{m}$$30-50\mu \mathrm{m}$30-50 mum30-50 \mu \mathrm{~m}$30-50\mu \mathrm{m}$ ) from calcite and fossil dissolution, weakening structural integrity. Uniaxial compressive strength ( ${\sigma }_c$${\sigma }_c$sigma_(c)\sigma_{c}${\sigma }_c$ ) decreased from 27.57 MPa to 17.94 MPa , with microcracks and fractured grains indicating mechanical degradation. HCl exposure caused yellowbrown surface discoloration from iron enrichment ( $0.805\mathrm{\%}\pm 0.012\mathrm{\%}$$0.805\mathrm{\%}\pm 0.012\mathrm{\%}$0.805%+-0.012%0.805 \% \pm 0.012 \%$0.805\mathrm{\%}\pm 0.012\mathrm{\%}$ by XRF), though EDX failed to detect iron due to detection limits or spectral interference. Potential oolites (grain size $0.05-3\mathrm{mm}$$0.05-3\mathrm{mm}$0.05-3mm0.05-3 \mathrm{~mm}$0.05-3\mathrm{mm}$ ) suggest additional matrix vulnerabilities. Calcite ( $40\mathrm{\%}$$40\mathrm{\%}$40%40 \%$40\mathrm{\%}$ ) and iron hydroxide ( $1\mathrm{\%}$$1\mathrm{\%}$1%1 \%$1\mathrm{\%}$ ) dissolution exposed the silicate matrix, producing coloured residues (hydrated iron
oxides), while quartz remained stable. Calcite dissolution increased porosity (po), creating voids, reducing bulk density ( $\varrho b$$\varrho b$ϱb\varrho b$\varrho b$ ) (potentially from $2.7\mathrm{g}/{\mathrm{cm}}^3$$2.7\mathrm{g}/{\mathrm{cm}}^3$2.7g//cm^(3)2.7 \mathrm{~g} / \mathrm{cm}^{3}$2.7\mathrm{g}/{\mathrm{cm}}^3$ to $2.4\mathrm{g}/{\mathrm{cm}}^3$$2.4\mathrm{g}/{\mathrm{cm}}^3$2.4g//cm^(3)2.4 \mathrm{~g} / \mathrm{cm}^{3}$2.4\mathrm{g}/{\mathrm{cm}}^3$ with $10\mathrm{\%}$$10\mathrm{\%}$10%10 \%$10\mathrm{\%}$ calcareous loss), and facilitating water, salt, or pollutant infiltration, accelerating weathering. Localized dissolution induced mechanical stresses, microcracks, and ${\mathrm{CaCl}}_2$${\mathrm{CaCl}}_2$CaCl_(2)\mathrm{CaCl}_{2}${\mathrm{CaCl}}_2$ crystallization, exacerbated by ${\mathrm{CO}}_2$${\mathrm{CO}}_2$CO_(2)\mathrm{CO}_{2}${\mathrm{CO}}_2$ gas bubble formation, with surface roughness increasing due to differential dissolution and iron hydroxide oxidation causing rusty hues. These changes increased porosity ( $po$$po$pop o$po$ ), brittleness, and reduced durability, particularly in humid or polluted environments, necessitating less aggressive conservation methods, such as weak acids or mechanical cleaning.
The reported zero error margins ( $\pm 0.000\mathrm{\%}$$\pm 0.000\mathrm{\%}$+-0.000%\pm 0.000 \%$\pm 0.000\mathrm{\%}$ ) for certain elements (e.g., $\mathrm{Zn},\mathrm{Pb},\mathrm{Rb},\mathrm{Zr},\mathrm{As},\mathrm{Y}$$\mathrm{Zn},\mathrm{Pb},\mathrm{Rb},\mathrm{Zr},\mathrm{As},\mathrm{Y}$Zn,Pb,Rb,Zr,As,Y\mathrm{Zn}, \mathrm{Pb}, \mathrm{Rb}, \mathrm{Zr}, \mathrm{As}, \mathrm{Y}$\mathrm{Zn},\mathrm{Pb},\mathrm{Rb},\mathrm{Zr},\mathrm{As},\mathrm{Y}$, and L.E.) arise from the specifications of the SciAps X-200 XRF spectrometer. For trace elements, concentrations at or below the instrument's limit of detection (typically $<0.01\mathrm{\%}$$<0.01\mathrm{\%}$< 0.01%<0.01 \%$<0.01\mathrm{\%}$ ) yield negligible uncertainty at the reported resolution. For light elements (L.E.), values are estimated by difference, producing no measurable statistical uncertainty.

Figure 12: XRD and EDX analysis of sample PE2-6 (T2).

Figure 14: XRD and EDX analysis graph of the sample PE2-4 (T2).

SEM-EDX analyses of limestone samples identified a composition of oxygen ( $50.50\mathrm{wt}\mathrm{\%}$$50.50\mathrm{wt}\mathrm{\%}$50.50wt%50.50 \mathrm{wt} \%$50.50\mathrm{wt}\mathrm{\%}$ ), calcium ( $39.74{\mathrm{wt}}^{\mathrm{\%}}$$39.74{\mathrm{wt}}^{\mathrm{\%}}$39.74wt^(%)39.74 \mathrm{wt}^{\%}$39.74{\mathrm{wt}}^{\mathrm{\%}}$ ), silicon ( $8.81\mathrm{wt}\mathrm{\%}$$8.81\mathrm{wt}\mathrm{\%}$8.81wt%8.81 \mathrm{wt} \%$8.81\mathrm{wt}\mathrm{\%}$ ), sodium ( $0.52\mathrm{wt}\mathrm{\%}$$0.52\mathrm{wt}\mathrm{\%}$0.52wt%0.52 \mathrm{wt} \%$0.52\mathrm{wt}\mathrm{\%}$ ), and chlorine ( $0.43\mathrm{wt}\mathrm{\%}$$0.43\mathrm{wt}\mathrm{\%}$0.43wt%0.43 \mathrm{wt} \%$0.43\mathrm{wt}\mathrm{\%}$ ) Fig. 13, Tab. 11. The presence of sodium (Na) and chlorine (Cl) confirms NaCl , indicative of salt crystallization, while silicon and calcium suggest silicates ( ${\mathrm{SiO}}_2$${\mathrm{SiO}}_2$SiO_(2)\mathrm{SiO}_{2}${\mathrm{SiO}}_2$ ) and carbonates ( ${\mathrm{CaCO}}_3$${\mathrm{CaCO}}_3$CaCO_(3)\mathrm{CaCO}_{3}${\mathrm{CaCO}}_3$ ), respectively. The high calcium content supports the classification of the stone as limestone, which is susceptible to saltinduced deterioration. Salt crystallization tests on T1 limestone samples from Tamentfoust fort elucidated intricate chemical and mechanical degradation processes driven by saline interactions under varying environmental conditions. NaCl reactions produce highly soluble ${\mathrm{CaCl}}_2$${\mathrm{CaCl}}_2$CaCl_(2)\mathrm{CaCl}_{2}${\mathrm{CaCl}}_2$ and ${\mathrm{NaHCO}}_3$${\mathrm{NaHCO}}_3$NaHCO_(3)\mathrm{NaHCO}_{3}${\mathrm{NaHCO}}_3$, which leach from the stone, compromising structural integrity, with the extent of deterioration modulated by humidity, temperature, and ion presence. Silicates ( ${\mathrm{SiO}}_2$${\mathrm{SiO}}_2$SiO_(2)\mathrm{SiO}_{2}${\mathrm{SiO}}_2$ ), while chemically resistant to direct NaCl interactions, undergo slow hydrolytic alteration in aqueous environments with additional ions, forming clay minerals or hydrated silicates, contributing to gradual long-term degradation. The mechanical impact of NaCl crystallization within pores exerts internal pressures of $2-5\mathrm{MPa}$$2-5\mathrm{MPa}$2-5MPa2-5 \mathrm{MPa}$2-5\mathrm{MPa}$ (lower than ${\mathrm{Na}}_2{\mathrm{SO}}_4$${\mathrm{Na}}_2{\mathrm{SO}}_4$Na_(2)SO_(4)\mathrm{Na}_{2} \mathrm{SO}_{4}${\mathrm{Na}}_2{\mathrm{SO}}_4$ 's $10-20\mathrm{MPa}$$10-20\mathrm{MPa}$10-20MPa10-20 \mathrm{MPa}$10-20\mathrm{MPa}$ ), inducing microcracking and stone disintegration, amplified by repetitive dissolution-crystallization cycles, resulting in significant mechanical damage over time. SEM analysis at $200\times (30\mu \mathrm{m})$$200\times (30\mu \mathrm{m})$200 xx(30 mum)200 \times(30 \mu \mathrm{~m})$200\times (30\mu \mathrm{m})$ (Fig. 15a) reveals a calcite-dominated matrix ( $50\mathrm{\%}$$50\mathrm{\%}$50%50 \%$50\mathrm{\%}$ ) with $30\mathrm{\%}$$30\mathrm{\%}$30%30 \%$30\mathrm{\%}$ elongated or irregular fossils ( $50-200\mu \mathrm{m}$$50-200\mu \mathrm{m}$50-200 mum50-200 \mu \mathrm{~m}$50-200\mu \mathrm{m}$ ) and angular quartz/feldspar grains (confirmed by XRD), characterized by a uniform, mildly porous cement texture (pores $<5\mu \mathrm{m}$$<5\mu \mathrm{m}$< 5mum<5 \mu \mathrm{~m}$<5\mu \mathrm{m}$ ) from low-compaction sedimentary origins. Sparse sub-parallel microcracks $(10-20\mu \mathrm{m})$$(10-20\mu \mathrm{m})$(10-20 mum)(10-20 \mu \mathrm{~m})$(10-20\mu \mathrm{m})$ suggest preparation-induced or internal stresses, with minimal mass loss $(\mathrm{\Delta }\mathrm{M}$$(\mathrm{\Delta }\mathrm{M}$(DeltaM(\Delta \mathrm{M}$(\mathrm{\Delta }\mathrm{M}$ :
$0.65\mathrm{\%}$$0.65\mathrm{\%}$0.65%0.65 \%$0.65\mathrm{\%}$ ) and no visible NaCl crystals, indicating limited surface degradation. At $2.20\mathrm{k}\times (3\mu \mathrm{m})$$2.20\mathrm{k}\times (3\mu \mathrm{m})$2.20kxx(3mum)2.20 \mathrm{k} \times(3 \mu \mathrm{~m})$2.20\mathrm{k}\times (3\mu \mathrm{m})$ (Fig. 15f), heterogeneously distributed nanometric pores ( $0.2-0.8\mu \mathrm{m}$$0.2-0.8\mu \mathrm{m}$0.2-0.8 mum0.2-0.8 \mu \mathrm{~m}$0.2-0.8\mu \mathrm{m}$ ), some occluded by iron hydroxides (bright contrast), are typical of limestone, facilitating saline solution penetration and increasing vulnerability to salt-induced damage. Calcite surfaces exhibit "honeycomb" dissolution streaks from ${\mathrm{Cl}}^{-}$${\mathrm{Cl}}^{-}$Cl^(-)\mathrm{Cl}^{-}${\mathrm{Cl}}^{-}$ion activity, while quartz remains uncorroded, reflecting its chemical resilience. A fine intergranular microcrack ( $<0.1\mu \mathrm{m}$$<0.1\mu \mathrm{m}$< 0.1 mum<0.1 \mu \mathrm{~m}$<0.1\mu \mathrm{m}$ ) at the calcite/quartz boundary serves as a stress concentration point, with limited NaCl precipitation suggesting minimal crystallization impact. Fossils ( $30\mathrm{\%}$$30\mathrm{\%}$30%30 \%$30\mathrm{\%}$ ) and open porosity weaken matrix cohesion, but partial pore blockage by weathering products, such as ${\mathrm{CaCO}}_3$${\mathrm{CaCO}}_3$CaCO_(3)\mathrm{CaCO}_{3}${\mathrm{CaCO}}_3$, reduces connectivity, mitigating the extent of damage [22].
SEM and EDX analyses of T2 limestone samples (Fig. 14), characterized surface and thin-section morphology and composition, revealing significant alterations following HCl exposure in aqueous conditions. SEM images showed a smoothed, etched appearance with discernible grain boundaries, most evident in (Fig. 16.c). At $376\times (20\mu \mathrm{m}$$376\times (20\mu \mathrm{m}$376 xx(20 mum376 \times(20 \mu \mathrm{~m}$376\times (20\mu \mathrm{m}$ scale), (Fig. 16.d) displayed microscale porosity, rough textures, and prominent cracks, characteristic of carbonate rock weathering, suggesting vulnerabilities to acid infiltration. At $2,14\mathrm{k}\times 25$$2,14\mathrm{k}\times 25$2,14kxx252,14 \mathrm{k} \times 25$2,14\mathrm{k}\times 25$ magnification, (Fig. 16.e) disclosed a highly porous, irregular microstructure with fragmented angular and elongated grains exhibiting sharp, fractured edges, alongside substantial cavities, including a significant void ( $\sim 30-50\mu \mathrm{m}$$\sim 30-50\mu \mathrm{m}$∼30-50 mum\sim 30-50 \mu \mathrm{~m}$\sim 30-50\mu \mathrm{m}$ ) surrounded by smaller pores and grain boundaries. This is indicative of pronounced dissolution and chemical etching. Smooth, rounded surfaces on presumed calcite grains reflect chemical dissolution via the reaction: ${\mathrm{CaCO}}_3(\mathrm{s})+2\mathrm{HCl}(\mathrm{aq})\to {\mathrm{CaCl}}_2(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})+{\mathrm{CO}}_2(\mathrm{g})$${\mathrm{CaCO}}_3(\mathrm{s})+2\mathrm{HCl}(\mathrm{aq})\to {\mathrm{CaCl}}_2(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})+{\mathrm{CO}}_2(\mathrm{g})$CaCO_(3)(s)+2HCl(aq)rarrCaCl_(2)(aq)+H_(2)O(l)+CO_(2)(g)\mathrm{CaCO}_{3}(\mathrm{~s})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{CO}_{2}(\mathrm{~g})${\mathrm{CaCO}}_3(\mathrm{s})+2\mathrm{HCl}(\mathrm{aq})\to {\mathrm{CaCl}}_2(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})+{\mathrm{CO}}_2(\mathrm{g})$, producing soluble ${\mathrm{CaCl}}_2$${\mathrm{CaCl}}_2$CaCl_(2)\mathrm{CaCl}_{2}${\mathrm{CaCl}}_2$, water, and gaseous ${\mathrm{CO}}_2$${\mathrm{CO}}_2$CO_(2)\mathrm{CO}_{2}${\mathrm{CO}}_2$. These observations align with recorded losses ( $\mathrm{\Delta }\mathrm{M}:1.64\mathrm{\%},\mathrm{\Delta }\mathrm{D}:0.92\mathrm{\%},\mathrm{\Delta }\mathrm{L}:0.66\mathrm{\%}$$\mathrm{\Delta }\mathrm{M}:1.64\mathrm{\%},\mathrm{\Delta }\mathrm{D}:0.92\mathrm{\%},\mathrm{\Delta }\mathrm{L}:0.66\mathrm{\%}$DeltaM:1.64%,DeltaD:0.92%,DeltaL:0.66%\Delta \mathrm{M}: 1.64 \%, \Delta \mathrm{D}: 0.92 \%, \Delta \mathrm{~L}: 0.66 \%$\mathrm{\Delta }\mathrm{M}:1.64\mathrm{\%},\mathrm{\Delta }\mathrm{D}:0.92\mathrm{\%},\mathrm{\Delta }\mathrm{L}:0.66\mathrm{\%}$ ) post-test, with etching notably intensified in carbonate-rich regions due to calcite's high solubility in acidic environments.