Civil Engineering Reference
In-Depth Information
from 153 different concrete compositions (precast and ready mix) were
provided by participants. The influence of the mix composition on the
RCM-value was analysed. Cement types used were mainly Portland cement
(CEM I 32.5R, 52.5N, 52.5R), blast furnace slag cement (CEM III/A 52.5
R, CEM III/B 42.5 LH HS), mixtures of these two cements and binders
comprising powder coal fly ash and Portland or slag cement. Binder contents
ranged from 300 to 450 kg/m
3
and water/binder ratios (w/b) from 0.33 to
0.65. The age at testing ranged from 28 days to 3 years, with most data at
an age around 28 days.
It was assumed that the RCM-value depends to a large extent on the type
of binder (cement type and reactive additions), w/b ratio and age. The data
were first grouped with respect to binder type: Portland cement (CEM I);
slag cement (CEM III/A or III/B, 50 - 76% slag); Portland and slag mixtures
(25-38% slag); Portland cement with fly ash (21-30% fly ash).
Within these groups, data of similar age were aggregated; ages of 28 to
35 days were considered as a single group. The influence of the w/b ratio on
D
RCM
was then analysed for each particular binder group at an age around
28 days. All fly ash present in the mixture was considered as cementitious
material, so
w
/
b
= water / (cement + fly ash). This analysis showed that the
D
RCM
-value is linearly related to the water/binder ratio:
(
)
(
)
D
RCM
28
d
=/
A
w
b
+
B
(15.1)
with
A
and
B
constants for particular cement types, see
Figure 15.2.
This
figure clearly shows that
D
RCM
and its
w
/
b
dependency strongly depend on
binder type. For Portland cement
D
RCM
is strongly influenced by
w
/
b
. For
cement with 50 to 76% slag this influence turned out to be less pronounced.
The regression coefficients (
A
,
B
) found for different binders are in good
agreement with those reported by Gehlen (2000). The data suggest that in
the range of practical
w
/
b
ratios between 0.35 and 0.55 (and present-day
concrete technology), minimum RCM-values apply that depend on binder
type.
Even though execution of the RCM test is much faster than the diffusion
test (NT Build 443), it is still labour intensive. For a quick impression of
the resistance against chloride ingress the two-electrode method (TEM)
for determining the electrical resistivity of concrete can also be used. In
(Breugel et al., 2008) a good correlation was reported between RCM and
inverse TEM results. Theoretical and empirical data support this correlation
(Andrade et al., 1994; Polder, 1997). Particularly for production control
the TEM test is suitable for a quick indication of the potential of a certain
mixture to meet prescribed diffusion levels. If resistivity testing indicates
non-compliance (i.e., a lower resistivity is measured than a predetermined
minimum value that corresponds to the fixed maximum RCM value), cores
can be taken and tested for RCM (Rooij et al., 2007).
