PSI - Issue 64

Marco Carlo Rampini et al. / Procedia Structural Integrity 64 (2024) 2141–2148 Author name / Structural Integrity Procedia 00 (2019) 000–000

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of the extracted samples from the external surface. In cases in which the extracted samples were completely destroyed, the same approach was used on the remaining walls of the cavity left behind. Only few points, chosen based on the results of electrochemical measurements, were subjected to carbonation assessment. 3.2. Results Figures 5, 6 and 8 show the preliminary results of tie rods S8, S9 and S6. For each figure, a schematic drawing of the element is reported, with the indication of defects detected on the external surface of the cementitious layer, and the relative pictures of the most significant ones. Carbonation depth results are also shown for the S8 and S9 rods, while for the S6 specimen it is still to be evaluated. Electrical resistivity mappings are reported, each one made of three measurements in the points A, B and C, and sixty/seventy measurements along the main axis of the tie rod, depending on its total length. Electrical resistivity is the parameter that quantifies the moisture content in a cementitious composite and can give a qualitative idea of the corrosion rate of a de passivated rebar included in it, i.e. a rebar that is experiencing active corrosion. Values higher than 1000 Ω∙m are representative of a cementitious composite in dry conditions and negligible corrosion rates, around 500 Ω∙m are characteristics of moderately wet conditions and low-to-moderate corrosion rates, and lower than 100 Ω∙m of wet conditions and high corrosion rates. In addition, the trend of the corrosion potential along the tie rod length is also presented, which is used to determine whether bars are still in passive conditions or are experiencing active corrosion. It is usually considered that steel rebar corroding in carbonated dry concrete are characterized by a corrosion potential between -100 and +100 mV vs CSE, while in carbonated wet concrete it decreases to values around -200 and -600 mV vs CSE, see Bertolini et al. 2013.

Fig. 5. Electrical resistivity mapping, corrosion potential and carbonation depth results for tie rod S8.

Figure 5 shows the electrochemical measurements and carbonation depth results for tie rod S8. Values of electrical resistivity higher than 1000 Ω∙m were often recorded, with some values around 500 Ω∙m only in few spots. Corrosion potential resulted mainly included in the range -200/+100 mV vs CSE in the central positions, and -330/-200 mV vs CSE towards the two ending parts. Carbonation depth was evaluated in four different positions (ID.S8-C1 to C4 in Figure 6), respectively in correspondence of two major and two minor corrosion potential drops identified. No carbonation was detected, as visible from the picture of the