Ultrasonic Evaluation of Mechanical Properties in Heritage Buildings Constructed with Córdoba Freestone

This study characterises the natural stone used in the Great Mosque of Córdoba (Spain) and establishes correlations to enable non-destructive, in situ assessment of the mechanical strength of the material. Quarry ashlars of the same biocalcarenite were tested to determine bulk density, ultrasonic wave propagation velocity (UWPV), and mechanical properties from uniaxial compression, splitting tension, and three-point bending tests (over 100 specimens). The stone showed no significant anisotropy or specimen size effects within the investigated ranges. Reference mechanical values were obtained, with a mean uniaxial compressive strength of about 6 MPa. A strong linear correlation was found between UWPV and compressive strength (R2 ≈ 0.86), supporting the use of ultrasonic testing to estimate compressive strength on site. In addition, flexural strength can be also estimated since it correlated strongly with compressive strength (R2 ≈ 0.95); in contrast, the correlation with tensile strength was moderate (R2 ≈ 0.31). The results provide validated relationships for Córdoba freestone that improve the reliability of ultrasonic tests for providing valuable information for structural analysis, maintenance, and conservation strategies for heritage buildings constructed with this kind of stone. The proposed approach offers a practical pathway for damage-free evaluation of mechanical performance in historical masonry.