Penetration chloride-induced corrosion

Concrete exposed to deicer salts, or to a marine environment is subjected to chloride and sodium loading. The ability of concrete to resist the penetration of chlorides and sodium is a primary design consideration in marine or cold environments. The ingress of chlorides into concrete is a major problem due to chloride-induced corrosion of the reinforcing steel and deicer salt scaling [a process by which a thin layer (< 1 mm) of concrete deteriorates from the surface of the concrete]. The penetration of sodium from sea water or deicer salts is generally... 

Alkanolamine-hased inhibitors have been tested in similar conditions. For ongoing chloride-induced corrosion with a chloride level of about 1-2 % by mass of cement, in mortar specimens no reduction in corrosion rate was found (Figure 13.6) except at low chloride concentrations. This is confirmed by two other studies [1,11,14] pre-corroded rebars in mortar (w/c 0.75, cover thickness 25 mm) did not show any detectable effect on the corrosion rate of embedded steel once active corrosion had been initiated, despite the fact that the specimens had low cover and porous mortar [14]. It seems that for penetrating or migrating inhibitors the favourable effects found in solution do not occur when applied to hardened mortar or concrete laboratory specimens with ongoing steel corrosion. It is thus necessary to look for information regarding the transport of inhibitor blends in mortar or concrete. 

Tests described above show that polymer-modified cementitious coatings may have good initial carbonation resistance, which may be lost due to weathering [7] and good chloride-penetration resistance [8], but no effect on chloride-induced corrosion rate [13]. 

The beneficial action of surface treatments generally hes in the fact that they prolong the period of initiation of corrosion. Once corrosion has begun, only those treatments that effectively obstruct the penetration of water, both hquid and vapour, will reduce the corrosion rate. This effect may be significant, in particular, if corrosion is due to carbonation [27]. Chloride-induced corrosion processes attract moisture so strongly that in general, surface treatments cannot stop it [13]. 

Figure 19.2 Definition of the depth of concrete removal for structures subjected to chloride-induced corrosion as a function of the present condition of the structure (time t ) and the estimated evolution of the chloride penetration damage at the time if when use of the structure is expected to finish (or new repair is planned).

Penetration of chlorides from seawater with subsequent corrosion of embedded steel represents a serious problem and threat to the durability and long-term performance of many concrete structures in marine environments. Recent field investigations of relatively new concrete structures in Norwegian harbors have shown that chloride-induced corrosion may occur already after a service period of approximately 10 years [1-2]. In order to obtain a more controlled durability and longterm performance of concrete structures in marine environments, a proper durability design should be carried out [3]. As part of such design, surface hydrophobation of the most exposed parts of the structure may be one of several protective measures that should be considered. 

S. Guzman, J.C. Galvez, J.M. Sancho, Cover cracking of reinforced concrete due to rebar corrosion induced by chloride penetration, Cem. Concr. Res. 41 (2011) 893—902. 

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