Assessment of the conservation state of masonry structures in monumental buildings by the integrated use of non-destructive ultrasonic techniques and mineral analyses.

Integrated in-situ Non-Destructive (ND) ultrasonic techniques and mineral analyses were carried out to assess the conservation state of masonry structures in monumental buildings. In situ measurements of ultrasonic longitudinal pulse velocity, were carried out in a representative monument in the hystorical center of Cagliari (Italy), to detect the elasto-mechanical conditions of the building materials. Ultrasonic measurements by surface or indirect transmission were performed using the step by step and refraction modalities. These different acquisition modalities were very effective in detecting the shallow altered areas of the building materials (step by step modality) and defining the thickness of the alteration (refraction modality). Based on the results of the ultrasonic investigations, a sampling was planned in the critical sectors of the façade to determine the mineral composition of mortar, bricks and building stones, as well as type and intensity of alteration. The collected samples were investigated by optical studies and X-Ray Diffraction (XRD) method. The integrated analysis of the acoustic and mineral data evidenced the correlation between the different acoustic signal propagation velocities and the intensity of alteration and type of materials. The analysis also provided significant quantitative information on the preservation state of the building materials.