The electrochemical behavior of steel reinforcement in conditions of corrosion and cathodic protection was studied, using electrochemical impedance spectroscopy ͑EIS͒ and compared to reference ͑noncorroding͒ conditions. Polarization resistance ͑PR͒ method and potentiodynamic polarization ͑PDP͒ were employed as well, in addition to ac 2 pin electrical resistance monitoring, thus deriving a comparison of the involved parameters, mainly polarization resistance and bulk electrical properties, obtained by all methods. It was found out that EIS is readily applicable for evaluating electrochemical behavior of the steel surface not only for corroding or passive state, but also in conditions of cathodic protection, although the interpretation of derived parameters is not straightforward and is related to the properties of the product layers, formed on the steel surface in the different conditions. For verification of the latter dependence, EIS, PDP, and PR measurements were performed additionally in cement extract solution, using steel samples from the previously embedded rebars in all technical conditions. The bulk matrix properties in passive, corroding, or under-protection conditions can be well defined by EIS. The evaluation of the electrochemical behavior of the steel surface, in terms of deriving polarization resistance, should take into account the crystallinity, morphology, and composition of the surface layers, which were investigated by scanning electron microscopy and energy dispersive X-ray analysis. In nondamaged reinforced concrete, steel remains passive due to the high alkalinity of the concrete pore solution ͑pH 12.5-13.5͒. If damages of the concrete cover and the concrete bulk matrix occur, depending on the aggressiveness of the environment, corrosion of the steel reinforcement will be initiated. The initiation and further evolution of the corrosion process will depend on the concrete pore network permeability and connectivity on one hand and the rate of penetration, amounts and concentration of aggressive substances in the environment ͑CO 2 , chlorides, sulfates͒ on the other. In the presence of chlorides, localized corrosion takes place as a consequence of passive layer breakdown. The rate of the process depends to a significant extent on the initial surface state of the steel surface, the chloride concentration, the chloride binding capacity of the bulk concrete matrix, etc. The chloride-induced corrosion process on steel reinforcement has been largely studied in concrete and in simulated pore solutions as well.1-21 Along with the localized corrosion on the steel surface, physico-chemical and structural transformations are taking place on the steel/cement paste interface. Further, the morphological alterations and certain distribution of product layers are influencing the mechanical properties of the reinforced concrete system as a whole.Impressed current cathodic protection ͑ICCP͒ is one of the protection techniques applied to such systems. Along with minimizing the corrosion process and preventing f...

The present study explores the formation of corrosion products on the steel surface ͑using as-received low carbon construction steel͒ in reinforced concrete in conditions of corrosion and subsequent transformation of these layers in conditions of cathodic protection ͑CP͒. Of particular interest was to investigate whether the introduced pulse CP ͑a cost-effective alternative to CP͒ will lead to similar or even more favorable conversion of the product layers on the steel surface, compared to conventional techniques. Qualification and quantification of the studied layers was performed using X-ray diffraction, X-ray photoelectron spectroscopy, and energy dispersive analysis, visualization of morphology and products distribution was achieved using environmental scanning electron microscopy. The steel surface was found to be covered by a layered, nonhomogeneous formation of products, differing in crystallinity and composition, comprising an inner layer, similar to Fe 3 O 4 , and an outer layer, composed of iron ͑oxy͒hydroxides and iron ͑oxy͒hydroxy-chlorides ͓i.e., a combination of ␣-, ␤, ␥-FeOOH, Fe͑O,OH,Cl͒, and Fe 2 O 3 ͔. The product layer in corroding specimens is a combination of low valent oxides and iron-oxy͑hydroxy͒chlorides, exhibiting a relatively rough morphology. The product layers in the protected specimens were far more compact. Cathodic protection reduces salinity around the steel bars, hence the inner product layer ͑mostly Fe 3 O 4 ͒ remains more uniform, whereas the outer layer exhibits reduced crystallinity. The favorable transformation phenomena were found to be more apparent under pulse CP conditions, attributed to the obviously beneficial effects of pulse CP in terms of enhanced chloride withdrawal from the steel surface and minor influence ͑less side effects͒ on the bulk concrete microstructure. The most common and important causes for reinforcement corrosion are either localized depassivation of the steel surface due to chloride ingress or more uniform corrosion due to acidification of the pore solution as result of carbonation of the cement paste. Cathodic protection ͑CP͒ has been found to be one of the most useful techniques for inhibiting chloride-induced corrosion in reinforced concrete.1 The fundamental mechanisms underlying the efficiency of CP techniques are strongly correlated to the morphology and transformations of product layers on the steel surface. The steel reinforcement used in the present study was as-received construction steel FeB500HKN ͑rebars, d = 12 mm, C Ͻ 0.22 wt %. Electrochemical impedance spectroscopy ͑EIS͒, polarizations resistance ͑PR͒ method, and potentio-dynamic polarization ͑PDP͒ were used for a comparative analysis of electrochemical parameters and corrosion behavior of the embedded steel in the reinforced concrete specimens presented here, in the relevant conditions of corrosion and CP, and the outcomes were reported previously.2 This paper pursues exploration of the formation, distribution, and morphological alterations of corrosion products in the reinforced c...

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