Issue 74

N. Meddour et alii, Fracture and Structural Integrity, 74 (2025) 227-261; DOI: 10.3221/IGF-ESIS.74.16

≤ 5 m for optimal defect analysis, it outperformed conventional approaches in identifying subsurface issues in historical structures. (Fig. 20.a) (mean 28.3°C) revealed warmer zones (orange/red, Δ T ≈ +3–5°C relative to the mean) on the left side, associated with biological growth forming air pockets that impede heat transfer, contrasting with cooler intact areas (blue/green, Δ T ≈ -1–3°C) indicating moisture retention due to variable stone porosity and capillary water absorption from precipitation or marine spray. Basal deviations suggested vegetation effects. A horizontal cool transect highlighted fissures and permeable joints, exacerbated by a saline environment promoting salt crystallization and efflorescence, causing mechanical stress. (Fig. 20.b) (mean 29.9°C) showed uniform warmth (orange/yellow, Δ T ≈ +2–3°C), with red zones indicating mortar detachment and honeycombing, and a cooler zone (blue, Δ T ≈ -1–2°C) near joints, reflecting moisture retention in porous and fractured joint materials. (Fig. 20.c) (mean 29.9°C) displayed dispersed cooler zones ( Δ T ≈ -1–3°C) across the stone, suggesting moisture pockets from internal fissures and delamination driven by non-uniform weathering and mineral variability. Saline conditions at Tamentfoust fort exacerbated deterioration through salt crystallization within pores and fractures, amplifying efflorescence and mechanical damage. Small-scale thermal variations, detected via infrared thermography indicated alveolarization, though results were moderated by resolution limits and environmental factors. Key degradation mechanisms include excessive moisture infiltration through joints, fissures, and the stone matrix, compounded by variable porosity. These conditions heighten risks of internal fractures, surface delamination, and joint degradation, further aggravated by saline-induced salt crystallization, which causes both mechanical and chemical damage to the stone structure.

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(b) (c) Figure 20: Thermographic images of the southern fort façade.

Durability tests Two durability tests were conducted on stone samples from Tamentfoust fort to assess material responses to physical mechanical stress and environmental degradation. The first test evaluated the salt crystallization resistance of T1 limestone samples, following standardized procedures (Fig. 21). The second test assessed resistance to accelerated aging in an acidic environment using hydrochloric acid (HCl) and moisture, conducted on T2 limestone samples. Both tests employed visual examination, uniaxial compressive strength ( σ c ), dry weight, and dimensional loss metrics. Analytical techniques, including crackmeter microscopy (Fig. 22), SEM-EDX (Fig. 15), petrographic analysis (Fig. 9), XRD, and XRF (Fig. 13), were used to characterize pre- and post-test alterations Tab. 8. Physical changes Soluble salts, alongside water, are primary agents of stone deterioration, causing crystallization stresses that exceed tensile strength, reducing it to powder, and micro-cracking. These salts, sourced from marine aerosols and pollution, contribute to hydration-related damage through multi-state salt transformations. Salt crystallization tests on cylindrical stone samples, conducted over 15 cycles, revealed a mean MDL-Loss (mass loss of ∆ M: 0.65%, <1%) Tab. 14, after an initial slight mass increase likely due to halite growth in pores >1 µm, indicating low susceptibility to salt weathering, classifying the stone as durable per ISRM and ASTM C88 standards. Mass loss ( ∆ M), accelerated between cycles 5–10 due to mechanical disintegration from salt-induced pore stresses, caused spalling and micro-cracking (Fig. 19). A non-linear diameter reduction ( ∆ D) exhibited cycle-dependent acceleration, reflecting anisotropic deformation tied to crystal orientation and stone heterogeneity, while a minor length reduction ( ∆ L), less pronounced than diameter loss, suggested axis-dependent mechanical strength influenced by porosity and crack propagation. Crystal expansion within pores drove cracking and structural weakening, with pore size correlating to crystallization pressure, yielding significant transverse dimension loss

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