Civil Engineering Reference
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content of recycled aggregates, both fine and coarse, did not have much
influence on the carbonation depth of concrete. However, concrete produced
with recycled aggregates tends to present slightly higher rates of carbonation
depth (about 5 mm) than the reference concrete. concrete mixes with 100%
coarse and fine recycled aggregates present carbonation depth rates that are
about 43% higher than those produced with 100% primary aggregates. The
higher the
m
(recycled aggregate/cement) ratio and the W/c ratio the greater
the concrete carbonation depths are. limbachiya et al. (2012) mentioned
that adding various proportions of coarse recycled aggregates as a partial
replacement of primary aggregates has resulted in a lower resistance to
carbonation, especially for the c30 and c35 concrete grades. The carbonation
depth and the rate of carbonation of concrete increase when the content of
recycled aggregates enhances.
evangelista and brito (2010) used only two rac with 30% and 100%
replacement of fine primary aggregates with fine recycled aggregates (FRA)
and obtained the following results concerning carbonation depth after 90 days
in the carbonation chamber: the 30% rac had a performance 27% better
than the reference concrete's and the 100% rac 35% worse. The authors
considered the first result anomalous and possibly due to the limited number
of specimens tested. however, they mentioned that results were compatible
with the ones from the compression strength test where all the rac mixes
achieved values very similar to the one of the reference concrete. Zega
and di Maio (2011) studied natural carbonation during 310 and 620 days
of concrete mixes with a partial replacement (20 and 30%) of Fra. These
authors reported a similar carbonation depth for mixes with different Fra
content, which they attribute to the low W/b ratio (0.41-0.43).
15.4.3 Combined effect of RAC and SCMs
corinaldesi and Moriconi (2009) mention that the carbonation depth after
1 year was 8.6, 5.9 and 6.5 mm, respectively, for the reference mix (reF),
recycled aggregates mix (REC) and recycled aggregates plus fly-ash mix
(rec + Fa). They concluded that, for mixes prepared with lower W/c ratio
and due to the refinement of the pore system, carbonation did not present
evidence of risks for reinforcement corrosion. This is due to the very low
permeability of these mixes, even if porous aggregates, such as recycled
aggregates, were used. abbas et al. (2009) found that mixes with Fa had
the greatest carbonation depth throughout the 140 days of exposure. This
behavior can be attributed to the pozzolanic action of the ScMs, which
consume ca(oh)
2
and consequently lower the alkalinity of concrete. The
carbonation coefficients of specimens with FA were the largest and were
almost twice the values of specimens without ScMs. The carbonation depths
of rac with and without ScMs fall in the expected range for structural-grade
