Civil Engineering Reference
In-Depth Information
is 3.2 times higher than for primary aggregate concrete. The concrete mix
containing natural sand and coarse recycled aggregates showed a carbonation
rate 1.8 times higher than for primary aggregates concrete. Fine and coarse
recycled aggregates had a water absorption value respectively of 12% and 6%
and were used pre-soaked. Katz (2003) found that the depth of carbonation
of the recycled concrete aggregates was 1.3-2.5 times greater than that of
the reference concrete. Coarse, medium and fine recycled aggregates were
used with water absorptions equal to (3%, 9% and 11%). according to the
author the properties of aggregates made from crushed concrete and the effect
of the aggregates on the new concrete (e.g. strength, modulus of elasticity)
resemble those of lightweight aggregate concrete, and similar considerations
apply when dealing with this type of aggregates.
otsuki et al. (2003) mention that carbonation the rate of concrete (W/b =
0.4) with coarse recycled aggregates is just slightly higher than for primary
aggregates concrete. They used coarse recycled aggregates with a water
absorption in a range of 3-5%. according to rao et al. (2007) the increase
in the carbonation depth of recycled aggregates concrete (rac) could be
attributed to the higher permeability of the recycled aggregates on account
of the presence of old mortar adhering to the original aggregate, and the
old interfacial transition zone (iTZ) between them. Tam et al. (2008) found
several acceptable correlations between carbonation depth and absorption
(
R
2
= 0.76); particle density (
R
2
= 0.73) and porosity (
R
2
= 0.77). Werle et
al. (2011) reported that the carbonation depth is influenced by the porosity
of the recycled aggregates. aggregates with a porosity lower than the matrix
porosity led to a reduction of the carbonation depth.
15.4.1 Curing
balayssac et al. (1995) found that
carbonated depth decreases rapidly when the
curing period increases from 1 to 3 days. after 18 months, for a concrete with
a cement content of 350 kg/m
3
, increasing the
curing
period from 1 to 28 days
halves the carbonation depth.
For concrete stored for 18 months, increasing
the curing period from 1 to 3 days increases the durability performance by a
value of 10% for a concrete with a cement content of 300 kg/m
3
and 50% for
a concrete with a cement content of 420 kg/m
3
; increasing the curing period
from 3 to 28 days still improves the durability performance by a value of
30% the concrete with the lowest cement content, but only by a value of
10% the concrete with the highest cement content.
Bai et al. (2002) mention that water-curing reduces sorptivity, which reflects
a finer pore structure that will, inhibit ingress of aggressive elements into
the pore system reducing carbonation. buyle-bodin and hadjieva-Zaharieva
(2002) found that the depth of carbonation is cut by half when concrete is
cured in water. The decrease in the depth of carbonation might be partially
