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due to the higher internal humidity content of this concrete. however, this
influence would be less pronounced for concrete with recycled aggregates
because of its higher porosity allowing faster water evaporation after curing.
lo and lee (2002) found that large differences in carbonation depth were
recorded between water-cured and air-cured samples but the difference
decreased with time. Water-cured concrete was found to have carbonated to
72% of the level reached by air-cured samples after 3 months of accelerated
curing.
atis (2003) showed that the longer initial curing period resulted in
lower carbonation depth. The effect is more marked with moist curing.
haque et al. (2007) studied lightweight aggregates, mentioning that the
greater the extent of initial water curing, the
lesser the depth of carbonation.
lo et al. (2008) found that mixes under hot water curing exhibited higher
carbonation than mixes under normal curing.
lo et al. (2009) stated that the
carbonation depth under accelerated curing was higher than that of concrete
under normal curing. The trend was more prominent for mixes with a higher
W/c ratio, than for the mixes, with a lower W/c ratio. one of the reasons
was that the samples were cured in hot water for 3 days and thereafter stored
in water for normal curing for 24 days. This indicates that the initial curing
period of PFa-incorporated concrete in hot water for 3 days resulted in
larger inter-pores in the cement paste.
limbachiya et al. (2012) mentioned that carbonation increase with W/b
and also that the water stored in the pore system of the recycled aggregates
and released throughout hydration process may contribute to the carbonation
process of the rac mixes compared to the control mixes. Moreover, it is
well recognized that carbonation of concrete occurs at an rh from about
40% to 70%. owing to the high water absorption of the coarse recycled
aggregates, the control mixes have generally lower moisture content than the
corresponding rac. This may also explain the low resistance to carbonation
of concretes containing coarse recycled aggregates.
15.4.2 RAC content
The carbonation depth increases with recycled aggregates content (levy
and helene, 2004). li (2008) cites research published in chinese journals
confirming that the recycled aggregates content has some influence on the
carbonation resistance of concrete. as the recycled aggregates content increases,
so does the carbonation depth. When the recycled aggregates content is 60%,
the carbonation depth increases as much as 62% compared with that of the
reference concrete. gomes and de brito (2009) mentioned that recycled
aggregates concrete shows just a slight increase in the carbonation depth
when compared with primary aggregates concrete. however, when more
than 50% of the volume is replaced by recycled aggregates the carbonation
depth increases about 10%. lovato et al. (2012) mentioned that the increased
