Formation Of Passive Film On Steel-concrete Interface

Within the environment of high pH, and within the absence of aggressive ions, soon subsequent to the beginning of hydration of cement, develops slowly a thin layer of passivation armor. Still within the new concrete begins the mechanism regarding the molecule diagram decreasing until the dissolution regarding the metal becomes negligible Brown, 2002; GAID 2004; HELENE, 1993; Tuutti apud BAUER, 1995; UZEDA, 1998. The mechanism passivation of armor off subsequent to the deposition of multiple layers and separates effectively the metal electrolyte Brown, 2002; FEDERAL HIGHWAY ADMINISTRATION, 2004; THAN hematite, hematite, hematite, hematite, GAVEL; Rengaswamy, 1998. It is compulsory to dissolve the metal that shape the passive layer. It consists film laminated with magnetite Fe3O4 adhered to conductive surface regarding the steel covered by insulating layer of molecules of ferric oxide, hematite Fe2O3, impermeable to ions, and of ferrous oxide FeO, which are stable products of corrosion CASCUDO, 1997; ST.

JOHN; POOLE, Sims, 1998 cited in Brown, 2002; THANGAVEL; Rengaswamy, 1998. Above the passive layer should be the deposition of calcium ferrite, resulting from the reaction of Fe2 OH 4 with Ca OH 3 BASIL, 1972 apud HELENE, 1993? 2Fe OH 4 + Ca OH 3 CaO Fe2O3 + 5 H2O. 1 Finally, the steel bars have also passivated are surrounded by the layer of Ca OH 2, from the reactions of cement hydration, due to the fact that the Ca OH 3 contributes to pH regarding the steel CASCUDO, 1997; GENTIL, 1982; THANGAVEL; RENGASWAMY, 1998. The presence of sodium hydroxide NaOH and potassium hydroxide KOH dissolved within the pore h2o also helps to maintain the high alkalinity HELENE, 1993; MEHTA Monteiro, 1994; SATO, 1998. The passivating layer is stable, provided that the pH price remains above 11.

5, and since within the absence of chloride ions MEHTA Monteiro, 1994. Once formed and in these conditions, no h2o and no oxygen can penetrate such a layer Taylor, 1992. Been shown that for the Fe-H2O system at 25 C and two atm, the diagram obtained bypotential, as measured by the standard hydrogen electrode versus pH shows a region formed by potential between +100 and -400 mV, typically located in concrete, with a pH between 12. 5, in which the iron metal is in a position passivation Pourbaix, 1974 apud HELENE, 1993; PANOSSIAN apud CASCUDO, 1997. A significant corrosion occurs only with pH values below 9 or above 14 HOU, CHANG, Hwang, 2004.

Mappings Stratfull 1973 apud HELENE, 1993, created within the early 70s to bridge deck with pathological manifestations typical action of deicing salts, formed the basis of ASTM C 876:1999, which gives general parameters to evaluate the corrosion of reinforcement.