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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2. Results Visual inspection. Apart from a compact rusty film visible overall directly exposed steel surfaces not protected by concrete and a circumscribed region where spalling cracks could be caught, and subsequently revealed by hammer strike (see Fig. 1c), the column was exempt from degradation (Fig. 1b). Hammer strike revealed that in the delaminating region an insufficient concrete cover, about 1 cm thick, was present.

a c Fig. 1. (a) side view (circles indicate the location of the coring site, the square indicates the parallelepiped-shaped diamond-cut location); (b) front view; (c) close view of the spalled region. Core sampling and neutralization assays. Two core samples of diameter 10.4 cm and lengths of 14 cm were extracted (Fig. 2a) in compliance with the Italian technical standards UNI 9944. Coring sites locations are shown in Fig. 1a. Concrete surfaces resulting from core sampling showed well-sorted grain size distribution and adequate concrete compaction. No visually detectable corrosion was found across the embedded bar segments (Fig. 2b). Neutralization assays on the two cores, performed by spraying a nebulized 1% phenolphthalein solution immediately after coring, failed to detect a carbonation front (Fig. 2c). Debriefing critical review of the testing activities conducted indicated, as a possible explanation for this circumstance, the UNI 9944 requirement which recommends performing the assays over surfaces mandatorily obtained by chisel and hammer splitting. Such recommendation is aimed at preventing deposition of basic powders ensuing from coring of the internal concrete layers over the external surfaces, which might be responsible for such misdetection. Consequently, a further sample extraction (sample C3) and a third phenolphthalein assay were scheduled and subsequently carried out over the concrete cover surface that was obtained, in particular, by chisel splitting in two halves of a parallelepiped-shaped diamond-cut sample (see Fig. 3). The split surface accordingly obtained was substantially free of dust and, with good approximation, orthogonal to the surface of the concrete cover. The average neutralization depth over the split surfaces, shown in Fig. 3c, resulted to be 6 mm, with a maximum value of 9 mm. b

a c Fig. 2. (a) sampled core; (b) close view of sampled bar cross-surface; (c) core shading after phenolphthalein spraying. b