The time required for corrosion initiation corresponds
to the time required for CO2or Cl
ions to diffuse to the
steel-to-concrete interface and activate corrosion. Extensive research work has been devoted to develop models that
predicts the time for corrosion initiation. Different models,
validated in field studies, for the rate of carbonation progression and chloride ingress which predict the time for
corrosion initiation can be found in the literature [5,6].
Some researchers intended to model the cracking behavior
caused by corrosion using nonlinear fracture mechanics
and/or finite element analysis[7–9]. In these models crack
propagation was governed by energy considerations. It
was concluded that stable crack growth can occur prior
to reaching the surface of the concrete. This implied that
additional expansion of corrosion products is necessary,
beyond the expansion required for crack initiation.
Although these models would better represent the cracking
behavior, they might be too complicated to be used by
practicing engineers. Few other researchers have attempted
to develop simple mathematical models for prediction of
time from corrosion initiation to corrosion cracking
[10–12]. A summary of these models is presented hereafter.
Bazant[10]suggested a mathematical model to calculate
the time between corrosion initiation and corrosion cracking of RC bridge decks. According to Bazant’s model, the
time from corrosion initiation to corrosion cracking is
mainly dependent on corrosion rate, cover depth, spacing
between steel reinforcing bars, diameter of the steel reinforcing bar, and properties of concrete such as tensile
strength, modulus of elasticity, Poisson’s ratio, and creep
coefficient. Bazant’s model assumes that all corrosion products create pressure on the surrounding concrete which
would underestimate the time to corrosion cracking[11].
The work of Bazant[10] was extended by Liu and
Weyers[11]. Liu and Weyers modeled the time from corrosion initiation to corrosion cracking based on the amount
of corrosion products required to cause cracking of concrete cover. The model includes same parameters used in
Bazant’s model but it takes into account the time required
for corrosion products to fill a porous zone around the steel
reinforcing bar before creating an internal pressure on the
surrounding concrete. In Liu–Weyers’s model, the rate of
steel mass loss caused by corrosion was assumed to
decrease as time progresses. The rate of steel mass loss
was assumed to be directly proportional to the square root
of the product of the corrosion current and the time of corrosion exposure. For the same time of corrosion exposure,
this assumption significantly underestimates the amount of
steel weight loss compared with that obtained by using the
well known Faraday’s law[13]. Underestimating the rate of
steel loss caused by corrosion would result in overestimating the time to corrosion cracking.
The time required for corrosion initiation corresponds
to the time required for CO2or Cl
ions to diffuse to the
steel-to-concrete interface and activate corrosion. Extensive research work has been devoted to develop models that
predicts the time for corrosion initiation. Different models,
validated in field studies, for the rate of carbonation progression and chloride ingress which predict the time for
corrosion initiation can be found in the literature [5,6].
Some researchers intended to model the cracking behavior
caused by corrosion using nonlinear fracture mechanics
and/or finite element analysis[7–9]. In these models crack
propagation was governed by energy considerations. It
was concluded that stable crack growth can occur prior
to reaching the surface of the concrete. This implied that
additional expansion of corrosion products is necessary,
beyond the expansion required for crack initiation.
Although these models would better represent the cracking
behavior, they might be too complicated to be used by
practicing engineers. Few other researchers have attempted
to develop simple mathematical models for prediction of
time from corrosion initiation to corrosion cracking
[10–12]. A summary of these models is presented hereafter.
Bazant[10]suggested a mathematical model to calculate
the time between corrosion initiation and corrosion cracking of RC bridge decks. According to Bazant’s model, the
time from corrosion initiation to corrosion cracking is
mainly dependent on corrosion rate, cover depth, spacing
between steel reinforcing bars, diameter of the steel reinforcing bar, and properties of concrete such as tensile
strength, modulus of elasticity, Poisson’s ratio, and creep
coefficient. Bazant’s model assumes that all corrosion products create pressure on the surrounding concrete which
would underestimate the time to corrosion cracking[11].
The work of Bazant[10] was extended by Liu and
Weyers[11]. Liu and Weyers modeled the time from corrosion initiation to corrosion cracking based on the amount
of corrosion products required to cause cracking of concrete cover. The model includes same parameters used in
Bazant’s model but it takes into account the time required
for corrosion products to fill a porous zone around the steel
reinforcing bar before creating an internal pressure on the
surrounding concrete. In Liu–Weyers’s model, the rate of
steel mass loss caused by corrosion was assumed to
decrease as time progresses. The rate of steel mass loss
was assumed to be directly proportional to the square root
of the product of the corrosion current and the time of corrosion exposure. For the same time of corrosion exposure,
this assumption significantly underestimates the amount of
steel weight loss compared with that obtained by using the
well known Faraday’s law[13]. Underestimating the rate of
steel loss caused by corrosion would result in overestimating the time to corrosion cracking.
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