Up to now, the only reliable data related to carbonation properties
of concrete are those obtained in natural environment where
concrete samples are exposed to real natural conditions over a long
term. This method, however, is very time consuming, normally taking
a few years. Therefore, various accelerated carbonation test
methods have been developed, using which carbonated samples
can be obtained in a short time and can be served as the basis
for predicting the carbonation behaviour of concrete under real
atmospheric environments. Note that, the CO2 concentrations used
in these test methods are significantly varied among countries. For
example, the CO2 concentration of 2% value is specified in the
report of DURACRETE [9], whereas it is 20% as prescribed in GB/T
50082-2009 [10]. The European standard EN 13295 [11] claims
that under certain testing conditions (i.e. 1% CO2, 21 ± 2 C, relative
humidity 60 ± 10%), the carbonation products formed would be
similar to those observed in naturally carbonated specimens.
Bernal et al. [12] stated that the CO2 concentration levels used in
an accelerated method should be in the range of 1.0–3.0% by volume
so that the carbonation process under natural environment
can be revealed. When concrete is exposed to high CO2 concentration
levels, the resulting carbonated concrete may be different
when compared to that formed under the natural environment.
of concrete structures.