Non-Destructive Defect Localisation and Sizing in Concrete Columns and Masonry Pillarl from Impact-Echo Testing

In order to proceed with the safety evaluation of a building, regulations of new generation introduce a performance formulation, that is the requirement to acquire data about and from the building: information about the foundations, the dimensions of structural members, possible local defects, decay areas in the material and repairings. This information has to be kept into account in the structural calculation models aimed to the safety check. The procedure is valid both for correctly preparing an adeguamento upgrading or improvement design of buildings in seismic areas, and for the rehabilitation of existing buildings and infrastructures. In this area, great is the contribution potential of non-destructive testing, when it can rely on easy-to-use methodologies, which are able to adapt to the operative work conditions of the building site. Nevertheless, the necessary link between NDT data interpretation and structural condition evaluation may become a limitation to the positive role that NDT may assume in the Civil Engineering field and in the construction industry. In fact, the translation from NDT results into structural and damage information has often constituted a barricade between NDT specialists and final users (designers, constructors, building inspectors, preservators and keepers) as the understanding of the NDT outcome is too often reserved to a restricted group of experts. For these purposes, it would be an advantage to dispose of NDT techniques which make an extensive and reliable use of images as diagnostic methodology. These would then make it possible to extract quantitative information relative to the structural and material condition directly from reconstructed cross-section images of the building element under test, bearing remarkable implications on the confidence in the assessment of the building knowledge. The impact-echo technique is an acoustic method which has shown, both in recent laboratory and on site experiments, to be able to supply the user with bi-dimensional images whose interpretation may overcome many of the typical limitations connected with the analysis of single signal waveforms and spectra. Precise data acquisition procedures are able to provide quantitative dimensional information directly readable on the images produced. Since its development, the technique has been applied to many kinds of structures, though, the vast majority, of the slab type (walls, slabs, flanges and webs of I-beams, etc.). Less common have been the applications to structures in which one of the geometric dimensions prevails on the other two. Few have been the applications of impact-echo testing on column members, piers and beams with circular, square and rectangular cross-section, even though these make up a large percentage of structural forms. In addition, their integrity evaluation is complicated by transversal resonances which make the analysis less straightforward. In all the known examples of these cases, the impact-echo data analysis and result presentation has taken place through single waveforms and spectra. In the sphere of an experimental research program about diagnostics of existing structures, laboratory experiences have been carried out via 2-D impact-echo testing on concrete and brick masonry specimens. The specimens exhibit circular or square cross-sections and contain artificial defects of various size at different depths. The presented preliminary results show significant plots of recorded data in the form of two-dimensional images comparable with the specimen’s sections. In these data plots, non relevant information, such as peaks due to cross-sectional element vibrations, may easily be discriminated from quantitative information related to internal defects. The defect location can be visually spotted and their depth and lateral extension may be evaluated with accuracy. The result’s discussion provides the interpretation criteria of the maps of data presented and of the peculiarities of...