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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 Role of carbonation in the corrosion process ‐ A marginal concern is found towards carbonation as a steel corrosion factor before 1975 (see, e.g., NCHRP 90). Carbonation is deemed not likely to proceed beyond few millimeters in a properly cast concrete, according to Mozer et al. (1965). Even after 1980, Collepardi et al. (1989) report that carbonation in absence of chlorides appears to be only a necessary, yet not sufficient, condition to trigger corrosion. ‐ On the other hand, in a considerable number of references from the beginning of the eighties onwards, carbonation is counted among the primary detrimental factors for corrosion. In Tuutti (1982) theoretical models are considered predicting relentless deepening of carbonation front. In this last reference, as well as in many subsequent others, carbonation is treated as a readily sufficient condition for corrosion initiation.  Degree of reliability credited to on-site electrochemical test methods for corrosion measurement ‐ Indig and Groot (1969) warn that even in a highly controlled lab set-up, electrochemical techniques alone are prone to errors that can lead to an erroneous rejection of a material that could provide satisfactory service. For half-cell methods, Kusenberger and Barton (1981), quoting Clear and Hay (1973), state (see page 57): “ Potentials have been noted to fluctuate between active and passive levels over a period of weeks ”. It is understood that such fluctuations pose a considerable problem for the interpretation of half-cell measurement. Analogous considerations can be carried out on other similar electrochemical on-site methods. ‐ From the beginning of the eighties onwards, increasing employment is found of indirect non-destructive on-site measurements of corrosion rates by electrochemical methods (such as half-cell potential and linear polarization methods) in total or partial replacement of direct sampling, see, e.g., Tuutti (1982), Andrade (2020), Elsener et al. (2003), and Ebell et al. (2018). The controversial picture exemplified by the selection of statements above reported motivated a research effort aimed at consolidating past and present knowledge on the evaluation of RC degradation and carbonation. An on-site case study was accordingly designed to independently elaborate a diagnostic reliability hierarchy, by comparing and selecting among different available methodologies, recommendations, and guidelines. The case study consists of an experimental campaign for evaluating the extent of carbonation and degradation underwent by a precast RC column which, taken from a lot never put into service after fabrication, remained for 20 years, after its prefabrication in 2000, fully exposed to weathering actions. The column was in an open storage area next to the Volturno river bank, aside from the concrete prefabrication plant situated in Caiazzo, in the north of the province of Caserta in Italy. The on-site tested element is shown in Fig. 1. The inspecting and testing activities carried out are reported in Table 1 with supporting references, while more details and references can be found in Bossio et al. (2021).

Table 1. Inspection activities and test methods carried out on the column and related references. Activity/Testing method N° Reference(s) Visual inspection of the column with the appraisal of concrete cover depths, degree of deterioration of concrete and steel, also by a hammer strike –

NCHRP Rep. 90 (Moore et al., 1970), ACI 562-16 (Kesner et al. 2018)

Concrete core sampling

2 –

UNI EN 12504-1/2002

Visual inspection of the drilled surfaces across cored samples and coring sites in search for possible oxidation evidence

–

Phenolphthalein assays over cores external surfaces

2 1

Partial fulfillment of UNI 9944 Partial fulfillment of UNI 9944

Phenolphthalein assay over concrete cover surfaces, obtained by chisel splitting from diamond-sawn parallelepiped-shaped sample Compressive strength tests carried out in a certified laboratory Phenolphthalein assays of powder samples obtained by drilling, according to Carbontest® methodology Corrosion rate mapping performed by half-cell potential method, using a Cu/CuSO4 counter electrode

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UNI EN 12390-1/2012 UNI EN 12390-3/2019

2

Felicetti (2008, 2010, 2012)

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ASTM C 876-15, UNI 10174:2020