subject: Fundamental mechanism of corrosion of reinforcement [print this page] Author: Ana Maria Author: Ana Maria
The onset of corrosion of reinforcement is not necessarily dependent penetration of aggressive agents. All it takes is the presence of electrolyte, oxygen and a difference potential (HELENE, 1993; Conciatori, 2002; SAKR, 2004). The aggressive agents that break or do not allow the formation of passive film and that can lead to corrosion of reinforcement are: sulfates, chlorides, carbon dioxide, nitrite, hydrogen sulfide, sulfur oxides, among others (HELENE, 1993). Depending on the conditions above, and within a certain range of electrochemical potential along the surface of the armor, can occur as oxidation reactions, according to the Equations 2.2 to 2.5 (AHMAD, 2003; FEDERAL HIGHWAY ADMINISTRATION, 2004; THANGAVEL; Rengaswamy, 1998). Anodic reactions: 3Fe + 4H2O Fe3O4 + 8H + + 8e-, equation 2.2 2Fe + 3H2O Fe2O3 + 6H + + 6e-, Equation 2.3 Fe + 2H2O HFeO2- + 3H + + 2e-, Equation 2.4 Fe Fe +2 + 2e-, Equation 2.5 Since the reaction releases electrons (2e-) regions anode, they are guided by steel in direction of the cathode areas are simultaneously received and where the reduction occurs dissolved oxygen to form hydroxyl. It creates, on the steel, an electric current, Icorr, the anode to the cathode, which forms a cell or electrochemical corrosion cell circuit, the flow of electrons in the steel and flow ions in the pore solution of concrete, because the oxidation of the metal is balanced by reduction of another substance at another point or region of the metal surface (ACI COMMITTEE 222 R, 1996; Ahmad, 2003; FEDERAL HIGHWAY ADMINISTRATION, 2004; SAKR, 2004; THANGAVEL; Rengaswamy, 1998). When the concrete is dry, oxygen penetrates by diffusion and reach the armor. Furthermore hand, when the concrete is wet, water (H2O) can achieve it, because the conditions exposure are important aspects that influence the corrosion of the armor (HELENE, 1993). These agents provide the cathodic reactions in which pH> 7 the reaction occurs
(LIU, 1996; Gentil, 1982) O2 + H2O + 2e-2 OH-, equation 2.6 and for pH
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