Civil Engineering Reference
In-Depth Information
aggregate replacement and according to lópez-Gayarre et al. (2011), up to
50% of replacement of natural aggregates by recycled ones, water absorption
increases up to 34%.
The permeability of recycled aggregates concrete is dependent mainly
on the quality of the matrix, since a matrix with low permeability will not
allow water to penetrate. However, since this matrix, for the vast majority
of concrete made routinely, is not of good quality, the quality of recycled
aggregate starts to be of great importance.
According rasheeduzzafar and Khan (1984; cited in Hansen, 1992), it
seems that the high water absorption of concrete with recycled aggregates
can be compensated by the production of concrete with a water/cement
ratio from 0.05 to 0.10 lower than that of conventional concrete. Therefore,
based on the experiments above, the performance of concrete produced
with recycled aggregates, the porosity, water absorption and permeability
is dependent on the quality of recycled aggregate and the cement matrix of
the new concrete.
14.4.4 Compressive strength
Several studies (ravindrarajah and Tam, 1985, 1987a; Hansen, 1992; Bairagi
et al., 1993; Ajdukiewicz and Kliszczewicz, 2002; Gómez-Soberón, 2002,
2003; Katz, 2003; Zaharieva et al., 2003; Topçu and Sengel, 2004; Xiao
et al., 2005; rakshvir and Barai, 2006; Tu et al. 2006; rahal, 2007; Xiao
and Falkner, 2007; Brito and Alves, 2010; Corinaldesi, 2010; lovato et
al., 2012) have shown that the compressive strength of concrete produced
with recycled aggregates is usually smaller than the concrete produced with
natural aggregates for the same consumption of cement. According to these
authors' data, these reductions can reach up to about 45% of the reference
concrete strength.
However, some authors (Hansen, 1992; leite, 2001; Ajdukiewicz and
Kliszczewicz, 2002; Khatib, 2005; Evangelista and Brito, 2007) showed
increases in concrete strength up to 33%, when natural aggregate was
replaced by the recycled ones. According to lópez-Gayarre et al. (2011),
the percentage of replacement does not affect the compressive strength
of concrete, being affected only by the quality of the recycled aggregates
employed. This discrepancy is due to the different variables involved, such
as the type of crusher used in the production of recycled aggregates, which
influence the form of it and consequently the content of voids in the concrete,
the type of cement used, the recycled aggregate composition, as well as the
methodology used, among other factors.
When the cement matrix of concrete produced with recycled aggregates is
less resistant than the recycled aggregate, this aggregate does not exert a great
influence on the concrete mechanical strength, since the cement matrix will
