Civil Engineering Reference
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and Tam, 1985), or an additive. Obviously, mechanical properties tend to
decrease.
Mukai et al. (1978; cited in Hansen, 1992), are more finicky. According
to these authors, concretes produced with the replacement of recycled
coarse aggregate demanded about 10 l/m³ or 5% more water than concrete
control, in order to achieve the same stated workability. When replacing both
coarse and fine aggregates by their recycled approximately 25 l/m³ or 15%
more water will be required. In order not to change the water/cement ratio,
a corresponding amount of cement must also to be added to the mixing.
Note, however, that the above values cited depend on the composition of
the recycled aggregates and the type of crushing process: they cannot be
taken as absolute.
14.4.3 Porosity, water absorption and permeability
Generally, the concrete made with recycled aggregates are characterized
by a high percentage of meso- and macro-pores, hence suggesting a greater
tendency to porosity with water absorption and leaching, than those prepared
with natural aggregates (Sani et al., 2005). According to studies by Gómez-
Soberón (2002), the distribution of pores in concretes with recycled aggregates
replacing natural aggregates is modified, while being the most sensitive for
high levels of replacement.
For concrete made with recycled concrete and/or mortar aggregate, this
porosity increases as the level of replacement of natural aggregate by recycled
aggregate rises. This gradually increases the content of paste in the concrete,
consequently increasing the pore volume, since the mortar is clearly more
porous than the natural aggregate (Gómez-Soberón, 2003; Etxeberria et al.,
2006; Evangelista and Brito, 2010; Brito and Alves, 2010).
For concrete with recycled red ceramic aggregates, Zakaria and Cabrera
(1996) comment that such concrete had 53% higher porosity than the
reference concrete. Also according to these said authors, since the recycled
red ceramic aggregate has a higher porosity than that of natural aggregates,
then concrete made with these aggregates possibly also has a high porosity.
The total porosity of these concretes is also affected by the high angularity
of recycled ceramic aggregates, and this generally increases the mixture pore
volume.
This increased porosity of the recycled aggregate concrete is then reversed
in higher water absorption. According to Hansen (1992), it is no surprise,
since the recycled aggregate concrete contains a large volume fraction
with the porous recycled aggregates distributed in the matrix, while the
conventional concrete has natural aggregates (less porous) distributed in the
same matrix. lovato et al. (2012) state that the concrete's water absorption
is more negatively affected by the fine aggregate replacement then the coarse
