Civil Engineering Reference
In-Depth Information
40
CEM I
CEM III > 50% slag
30
CEM I, 18 -30% fly ash
Fly ash, extrapolated
20
10
0
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
w/b
15.3.2 Modelling chloride ingress
In the DuraCrete model, the evolution of chloride profiles is approximated
with:
⎡
x
⎤
C
(
x
,
t
)
=
C
−
(
C
−
C
)
erf
⎢
⎣
}
⎦
(15.2)
s
s
i
{
⎢
4
k
D
(
t
)
t
where
C
(
x
,
t
) is the chloride content (all chloride contents in this chapter
are expressed in percentage by mass of binder) at depth
x
at time
t
,
C
s
is the
surface chloride content,
C
i
the initial chloride content of the concrete,
k
is
a correction factor,
D
(
t
) is the apparent diffusion coefficient as a function of
time (see below) and
t
is time. The surface chloride content was assumed to be
independent of mix composition for reasons of simplicity: 3.0% for marine
structures (Polder and Rooij, 2005; Rooij and Polder, 2005) and 1.5% for
land-based structures (exposed to de-icing salts), based on data from (Gaal et
al., 2003). The initial chloride content was taken equal to 0.1%.
The apparent diffusion coefficient
D
(
t
) is multiplied by a correction
factor
k
to obtain the chloride diffusivity of concrete in a real structure. This
correction factor depends on binder type, environment and length of wet
curing. Some of the deviations from pure diffusion behaviour are included
in this parameter. The
k
-values were taken from DuraCrete or interpolated
(Duracrete, 2000). The critical chloride content was taken to be equal to
