GNGTS 2018 - 37° Convegno Nazionale

638 GNGTS 2018 S essione 3.2 ENGINEERING AND URBAN GEOPHYSICS TO MONITOR REINFORCED CONCRETE STRUCTURES L. Capozzoli, G. De Martino, E. Rizzo Istituto di Metodologie per le Analisi Ambientali, Consiglio Nazionale delle Ricerche (CNR-IMAA) Tito (PZ), Italy Hydrogeosite Laboratory, Marsico Nuovo (PZ), Italy Introduction. The use of reinforced concrete (RC) technologies into the engineering field of the building and civil infrastructures represent probably the most important discovery of the 19th century. At the same time the RC technology represents an economic way to realize building and for this reason in a large number of country has become the most used technology. In Italy, in the last decades, the structures realized with RC technology have exceeded those realized with technologies based on use of brick and stone masonry [1]. However RC technology is affected by very dangerous degradation phenomena that could be reduce strongly the life time of engineering structures. The real cause of this problem involving all the RC structures is due to heterogeneity of the material characterized by a mixture of concrete where steel rebar are placed depending on the need imputable mainly to mechanical stresses. So the interaction between steel and concrete is one of the causes that generates degradation. Among the different causes three are the one most detected and recognizable: a) corrosion for flow of chloride ions, b) cracks, fractures or delamination induced by mechanical stresses, c) voids or carbonation due to water or moisture (Apostolopoulos, C.A. et al., 2013). In addition to the degradation mechanisms (definable for simplicity as local problems) that involve the RC structures, other effects that could cause fails for the structures interesting the global behaviour of all engineering buildings included precast or realized in situ RC structures. This is the case of settlement foundations or seismic vulnerability or low bearing capacity of structures for obsolescence or age (Breysse 2012). Geophysics can offer effective tools to aid engineers and public stakeholders to monitor and verify the state of conservation of RC elements subjected to “local” or “global” mechanisms of degradation. A novel sub-discipline, called Urban Geophysics, has recently been developing in the field of geophysics for analysing limits and potentialities of well-known geophysical techniques in urban and industrialized areas. The urban geophysics represents, most likely, the only way to characterize the subsoil ensuring a good resolution for the obtainable information and interfering little or nothing with the life of the investigated area. Unfortunately, not all the geophysical techniques are applicable in urban areas for the strong noise due to the presence of metallic structures or highly insulating layers (i.e. asphalt) that often limit the use of electrical and electromagnetic methods. However, good results are achievable with applications of electrical resistivity measurements and ground penetrating radar so much to investigate structural elements as to monitor the stability of civil structures (Capozzoli and Rizzo, 2016). The paper presents some real cases where electric and electromagnetic geophysical tests are applied in combined mode to identify the possible cause of degradation of structures and some laboratory experiences where the usefulness of geoelectrical measurements (performed without use of classical and invasive electrodes) and ground penetrating radar has been tested to identify their effective contribution among non-invasive tests. Electrical resistivity technique and Ground penetrating radar for civil engineering issues. ERT is a geophysical active method belonging to the resistivity techniques and is based on the introduction of direct current with a couple of electrodes inserted in the ground and the subsequent recording of the potential difference generated in the soil thanks to the passage of the electrical current. The theoretic basis of this well-known technique lies with the Ohm’s law and the target of this method is the localization of the electrical resistivity variations of the subsurface materials induced by the presence of anomalous bodies into the soil. Generally, a switched square wave is the current waveform used (Binley and Kemna, 2005) and an advanced “multimeter” called georesistivimeter is used to implement particular sequence for generating