PSI - Issue 46

Roberto Serpieri et al. / Procedia Structural Integrity 46 (2023) 112–118 R. Serpieri, A. Bossio, G. Faella, G. Frunzio, M. Guadagnuolo / Structural Integrity Procedia 00 (2019) 000–000

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by the approximate magnification factor of 2, between real thickness and powder thickness, also indicated by Felicetti (2010,2012) regarding the instrumentation and measurement parameters therein employed. Corrosion potential measurements . Five corrosion potential measurements were performed according to ASTM C876 15 (2015), following the recommendations by Elsener et al. (2003) and Ebell et al. (2018) and employing instrumentation with a copper/sulphate copper [Cu/CuSO4] electrode. The measurements were performed in 5 points of the column and the corresponding readings in mV are: -222, -252, -236, -244, -261. The following interpretation criteria are applied to this data: values higher than -200 mV were interpreted as an absence of corrosion, values in the range (-200 mV, -350 mV) were considered indicative of an increased probability of corrosion initiation, while values lower than -350 mV were considered representative of corrosion initiation. Accordingly, the five measured values can be interpreted as indicative of minor corrosion initiation processes. Concerning this reading, it is worth remarking that measured potentials were found to be affected by variations in the concrete cover thickness (Bossio et al., 2020) and that some degree of arbitrariness is found in the literature concerning the definition of these thresholds. It has been also recalled that the fluctuations mentioned by Kusenberger and Barton (1981) over periods of weeks (see page 57) seem to pose a considerable problem for the intersubjective interpretation of half-cell measurement. Strength tests. Compressive strength tests were carried out in a certified laboratory according to UNI EN 12390-1/2012 and UNI EN 12390-3/2019. Cylindrical samples were cut and ground in smaller specimens of height equal to the diameter of 10.4 cm. Densities of 2275 and 2259 kg/m 3 and strengths of 45.22 and 53.53 MPa, computed according to UNI EN 13791, were calculated. These values are in full accordance with the design values of 45 MPa of the technical documentation retrieved from the archives of the prefabrication plant and are interpreted as an indication of good concrete quality and absence of degradation in concrete. 3. Discussion and conclusions The main result of the diagnostic tests for the evaluation of degradation over a precast column is that, after 20 years of weathering, corrosion in embedded bars has been detected only in very limited superficial regions, where the insufficient thickness of concrete cover can be revealed by a hammer impact delamination. The only degradation found in concrete is delamination in these regions. No visually detectable sign of corrosion, or even oxidation, was found in the sampled bar segments. With the only exclusion of limited regions affected by an insufficient concrete cover, the corrosion initiation time is found to be significantly higher than 20 years. Further lessons learned in diagnostic reliability evaluation of degradation of RC elements from the case study presented in this paper are the following.  Core sampling with a visual inspection of embedded bars is identified as a diriment golden standard for diagnosis. If core sampling had not performed, a reliable judgment of durability and expected service life would have been much more difficult and affected by controversial elements for judgment as well as by arbitrariness elements invalidating the diagnostic significance of the campaign.  The commercial exploitation and some recent introduction of new methodologies do not grant per se increased reliability in evaluating degradation compared to most elementary visual inspections. Acknowledgments Sviluppo Silicalcite S.a.s. is gratefully acknowledged for making available the precast structural element. Testing support and equipment provision by Tecnolab S.r.l. is also gratefully acknowledged.

References ASTM, C 876-15, 2015. Standard test method for corrosion potentials of uncoated reinforcing steel in concrete. Andrade, C., 2020. Electrochemical methods for on‐site corrosion detection. Structural Concrete, 21(4), 1385-1395.