Seismic reliability of deteriorating reinforced concrete (RC) bridges - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 508

structures. Following the review on the deterioration mechanisms and
resulting damage, an assessment tool to quantify capacity and reliability
loss associated with these deterioration modes is presented. In addition,
an example is provided.

19.2.1 Corrosion of steel in concrete

The mechanisms of corrosion have been widely reported throughout the
literature and a comprehensive literature review is beyond the scope of this
chapter. For more comprehensive information, the authors direct the reader
to the American Concrete Institute's Committee 222 documents. Corrosion
is the electrochemical reaction between a metal and its environment. For
RC structures, the cementitious material (often concrete) provides a protec-
tive barrier against the aggressive elements in the surrounding environ-
ment. However, these aggressive elements can penetrate the protective
concrete barrier and react with the reinforcing steel. When the reinforcing
steel corrodes, a corrosion product is formed that is larger in volume than
the original base steel. This corrosion product forms within the concrete
voids and pores, placing the concrete in tension. Because cementitious
materials are weak in tension, the formation of corrosion products com-
monly results in cracking and spalling of the cementitious cover. Once
cracked or spalled, the protective capacity of the cementitious cover is
further reduced, making the reinforcement even less protected and more
susceptible to further deterioration.
Chlorides accelerate the corrosion process. Chlorides can be introduced
to the concrete from exposure to saltwater, deicing or anti-icing chemicals,
or can be introduced to the concrete as part of the constituent materials.
Chloride-induced corrosion of steel reinforcement requires that suffi cient
chlorides be present at the steel-cementitious materials interface and that
both oxygen and water are available (González et al. 1993; López and
González 1993; Balabanić et al. 1996; Hussain et al. 2012). The availability
of suffi cient quantities of these elements or compounds will result in active
corrosion of the steel reinforcement.
The mechanisms of chloride-induced corrosion have not been thoroughly
defi ned. However, at locations where the mill-scale is discontinuous, a
passive fi lm likely exists. Passive fi lms have been reported to be thin layers
of oxides that occupy the reactive atom sites on the metal surface. By occu-
pying these reactive sites, the fi lm prevents metal atoms from reacting with
the ions in the environment, thus preventing the corrosion process from
initiating. Ghods et al. (2011a, b) showed that the passive fi lm on steel in
highly alkaline environments is approximately 5 nm (2

10 −4 mils) thick
and is composed of a thick, porous outer layer over a thin, dense inner layer.
The inner protective layer was reported to be mostly composed of Fe 2+

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