Civil Engineering Reference
In-Depth Information
d
t
≤
T
⎧
⎪
⎪
b
0
corr
(
)
=
(
)
−
164
.
(
)
071
.
dtT
d
−
1 0508 1
.
−
w c
t
−
T
T
tT
tT
<≤
[16.31]
b
corr
b
0
corr
co
rr
f
0
>
f
where,
d
b
(
t
|
T
corr
)
=
diameter of bar at
t
and
T
corr
=
the corrosion initiation
time given by:
11
q
(
−
)
−
2
⎧
⎫
d
kkkD t
2
C
C
⎪
⎩
⎡
⎢
⎛
⎜
⎞
⎟
⎤
⎥
⎪
⎪
c
−
1
cr
[16.32]
TX
=
erf
1
−
corr
I
()
q
4
⎪
cs
etc c r f
factor
representing the infl uence of test methods to determine the empirical dif-
fusion coeffi cient
D
c
,
k
c
where
d
c
=
reinforcement cover depth,
k
e
=
environmental factor,
k
t
=
=
parameter that accounts for the infl uence of
curing,
t
ref
model uncertainty coeffi cient to
account for the idealization by Fick's second law,
C
cs
=
reference period for
D
0
,
X
I
=
=
A
cs
(
w
/
b
)
+
ε
cs
is the
chloride concentration on the surface,
w
/
b
=
water to binder ratio,
A
cs
and
ε
cs
are the model parameters,
C
cr
=
critical chloride concentration, and erf(
⋅
)
for
C
s
<
C
cr
. Since
C
cr
and
C
cs
are independent random variables,
P
(
T
corr
=
is the error function. In Eq. (16.32),
T
corr
<
∞
for
C
s
≥
C
cr
and
T
corr
=
∞
) > 0.
Table 16.3 lists the values of the model parameters for two levels of
exposure to chlorides: atmospheric and splash. The atmospheric exposure
level refers to the condition where moisture in the atmosphere contains
chloride ions. The splash exposure level refers to cyclic spraying of salt
water (containing chlorides) on the structure's surface. The values shown
∞
Table 16.3
Model parameters for prediction of T
corr
Standard
deviation
Standard
deviation
Mean
Mean
Variable
Atmospheric
Splash
Distribution
D
c
220.9
(mm
2
/yr)
801.01
(mm
2
/yr)
801.01
(mm
2
/yr)
Normal
q
0.362
0.245
0.362
0.245
Beta
k
e
0.362
0.245
0.362
0.245
Gamma
k
c
0.8
0.1
0.8
0.1
Beta
k
t
0.832
0.024
0.832
0.024
Normal
X
I
1
0.05
0.265
0.045
Lognormal
A
cs
2.565
0.356
7.758
1.36
Normal
ε
cs
0
0.405
0
1.105
Normal
C
cr
0.80
0.10
0.80
0.10
Normal
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