PSI - Issue 11

Gibson R. Meira et al. / Procedia Structural Integrity 11 (2018) 122–129 Meira et al./ Structural Integrity Procedia 00 (2018) 000–000

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1. Introduction Concrete is an alkaline material with pHs of its liquid phase between 12.5 and 13.5, according to Mehta and Monteiro (2008). In reinforced concrete structures, this condition provides the formation and stability of a passive film composed of a thin layer of oxides, which are strongly adhered to the steel surface. This film protects the reinforcement against further corrosion, according Helene (1993) and Cascudo (1997). Concrete carbonation is a physical and chemical phenomenon that generates a front of pH reduction that, when reaches the reinforcement level, promotes the passive film breakdown, which is the responsible for the chemical protection of the armature. According to Mehta and Monteiro (2008), Andrade (1988) and Tuutti (1982), represent the beginning of the corrosion process. Methods to prevent or rehabilitate structures subjected to reinforcement corrosion have been widely used abroad. One of them is the use of galvanized reinforcement. The use of this kind of material is a feasible alternative both in environments subject to carbonation and to the action of chlorides. The generation of the passive film in galvanized steel bars conceals the formation of a thin layer of calcium hydrozincate strongly adhered to the steel surface. This formation only occurs in media with pHs below 13.3. For media with higher levels of alkalinity, such formation does not happen efficiently, endangering the stability of the reinforcement, according to Macias and Andrade (1990). Although some studies have been carried out, Farina and Duffó (2007) point out the need for studies on the effect of concrete carbonation on the corrosion resistance of galvanized steel bars. For Maahn and Sorensen (1986) the galvanized reinforcement remains passive even after the carbonation of the concrete, keeping the reinforcement corrosion levels in the same order of magnitude as those in non-carbonated media, whereas the conventional reinforcement in carbonated concrete can have up to ten times higher corrosion levels. This way, the present study aims to evaluate the behaviour of galvanized reinforcements in carbonated and non- carbonated media, focusing on the limiting alkalinity below which the generation and stabilization of the galvanized film can be guaranteed and thus the higher performance of this type of reinforcement in comparison with carbon- steel reinforcements.

Nomenclature Eq

equivalent of the metal species involved in corrosion, in grams (g)

i corr

corrosion current density (μA /cm²)

metal density (g/cm³)

d

2. Experimental work 2.1. Reinforcements treatment

Firstly, all reinforcement bars were cut into 100 mm segments. The non-galvanized bars were bevelled on the ends with emery, and mechanically cleaned with a steel bristle brush and then subjected to a chemical pickling, with reference to the American Standard ASTM G1 (2011). After the cleaning process, the bars were painted with epoxy resin, leaving only a central length of 30 mm exposure. Once hardened the resin, the non-galvanized bars were subjected to a second chemical pickling process. 2.2. Elaboration of test cells (TC) For each test condition, two cells were made (one for galvanized and the other for non-galvanized bar), each one containing a single CA 50 bar with diameter of 6.3 mm. In the array of cells, such bars are the working electrode, while a carbon/graphite bar was deployed as a counter electrode. In addition, 300 ml of alkaline solution were used in each cell. The solutions used to simulate the liquid phase of concrete are described in Table 1. All solutions were