Geology Reference
In-Depth Information
1. INTRODUCTION
water-to-cement ratio, ambient temperature, rela-
tive humidity, concrete age, free chloride content,
and binding capacity, are considered to obtain a
precise prediction of the chloride content in dif-
ferent depths of RC members with the progres-
sion of time. By comparing the chloride content
values with certain critical thresholds suggested
in the literature, the corrosion initiation time is
estimated. After corrosion initiation, the time-
dependent characteristics of corroded bridges are
identified through the extent of the cracking and
spalling of the concrete cover, reduction of the
steel bar cross-section area, and decrease in the
yield strength of reinforcing bars. Based on that,
the probabilistic life time fragility parameters of
a group of RC bridges with different structural at-
tributes are evaluated over the time using fragility
analysis procedure.
Furthermore, the life-cycle cost of RC bridges
under corrosion attack is studied in this chapter.
The total life-cycle cost of the bridge is calculated
from the present value of the construction cost,
inspection and maintenance costs, serviceability
and earthquake-induced failure costs, and finally
user costs associated with them. These costs are
reviewed in detail and the relevant assumptions
are discussed to provide a more realistic estimation
of the total cost. Among the mentioned costs, a
special attention is paid to the serviceability and
earthquake-induced failure cost. The serviceability
failure cost is incurred from necessary repair and
replacement actions due to the concrete cover
spalling and steel rebar corrosion while the earth-
quake-induced failure cost is due to the repair and
rehabilitation actions after a specific seismic event
and is dependent on the occurrence probability of
different damage states. This cost is estimated here
from the results of probabilistic life-time fragil-
ity analysis by introducing a performance index
which represents the expected performance of a
corroded bridge under a particular seismic hazard
risk. This index is updated regularly over the time
and takes into account the combined effects of
seismic hazard and chloride-induced corrosion in
the calculation of life-cycle cost of RC bridges.
From a long-term point of view, the durability
of reinforced concrete (RC) highway bridges is
significantly impacted by the deterioration of
their structural members. When investigating
the damaged bridges, the deterioration caused
by the corrosion of reinforced concrete members
is usually found to be one of the main sources
of structural degradation which may eventually
result in the serviceability failure of bridges under
service or extreme loading conditions. An accurate
estimation of the extent of degradation during the
structure's life-cycle provides both engineers and
decision-makers with valuable information which
helps to ensure the safety of bridges while reduc-
ing the associated costs. Towards this goal, the
current chapter focuses on the corrosion process
caused by the chloride ions attack and evaluates
its effects on the life-cycle performance and cost
of RC bridges.
Chloride-induced corrosion is one of the
deterioration mechanisms caused by the rapid
intrusion of chloride ions into the concrete. This
mode of corrosion is expected when the bridge
is exposed to aggressive environments (e.g.,
coastal environments or the application of deicing
salts). The penetration profile of chloride ions in
a reinforced concrete member demonstrates the
highest chloride content near the surface with a
decreasing trend towards the depth of the member.
The chloride transport mechanism in concrete is
a complex phenomenon that may occur in several
forms, such as ionic diffusion, capillary suction,
and permeation. When the concentration of chlo-
ride ions in the pore solution within the vicinity of
reinforcing bars becomes high enough to depas-
sivate the protection film of the reinforcement, the
layers of rust start to form on the reinforcing bar
surface and the corrosion of steel begins.
In this chapter, an integrated computational
methodology is developed to simulate the penetra-
tion of chloride ions into the reinforced concrete
members. Through a comprehensive study, the
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