Maria Laminated
Formation of passive film on the steel-concrete interface
In the high pH environment, and in the absence of aggressive ions, shortly after the onset of cement hydration is slowly developing a thin passivation layer of armor. Also in the fresh concrete corrosion rate mechanism starts continues to decrease until the dissolution of metal becomes negligible (Brown, 2002; GAID 2004 HELENE, 1993 apud Tuutti BAUER, 1995; Uzeda, 1998).
The mechanism passivation of the armor off after the presentation of several layers and effectively separates the metal electrolyte (Brown, 2002 Federal Highway Administration, 2004; THAT hematite, hematite, hematite, hematite, hammer; Rengaswamy, 1998).
It is necessary to dissolve the metal forming the passive layer. He rolled up his movie magnetite (Fe3O4) joined conductive surface of the steel covered by an insulating layer of molecules of iron oxide, hematite (Fe2O3), impermeable to ions and ferrous oxide (FeO), which are stable products of corrosion (Cascudo, 1997 ST. JOHN: Poole, Sims, 1998 cited in Brown, 2002; Thangavel; Rengaswamy,
1998).
Beyond the passive layer can be deposited calcium ferrite, resulting from the reaction of Fe2 (OH) 3 with Ca (OH) 2 (basil, HELENE Apud 1972 1993): 2Fe (OH) 3 + Ca (OH) 2 + CaO Fe2O3 • H2O 4. Equation 2.1
Finally, the passivated steel bars are also surrounded by the layer of Ca (OH) 2 of the cement hydration reactions due to Ca (OH) 2 contributes to the pH of the steel (Cascudo, 1997 NICE, 1982; Thangavel; Rengaswamy, 1998).
The presence of sodium hydroxide (NaOH) and potassium hydroxide (KOH) dissolved in pore water also helps maintain the high alkalinity (Helena, 1993; MEHTA Monteiro, 1994; SATO, 1998). The passivation layer is stable if the pH is maintained above 11.5, and since, in the absence of chloride ions (Mehta Monteiro, 1994). Once formed and in these conditions, no water, no oxygen can penetrate the layer (Taylor, 1992).
It has been shown that for the Fe-H2O 25 ° C and 1 atm, the diagram obtained by
potential, measured by the standard hydrogen electrode as a function of pH shows a region formed in potential between +100 mV and -400, typically found in the concrete with a pH between 12.5 and 13.5, where the metal plate is in a position passivation (Pourbaix, 1974 apud HELENE, 1993 apud Cascudo Panossian, 1997). A significant corrosion occurs only at pH values below 9 or above 14 (HOU, CHANG, Hwang, 2004).
Stratfull Assignments (1973 apud HELENE, 1993), presented at the 70 to the bridge deck with typical manifestations pathological action of deicing salts, formed the basis of ASTM C 876:1999, which sets broad parameters for assessing reinforcement corrosion.
About the Author
Ana Maria is Civil Engineer and expert in Concrete. Visit Betoneira and see the Betoneiras Usadas
Proyecto diseño de Puente de Madera con Arcos Inclinados 3
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