Civil Engineering Reference
In-Depth Information
According to Olorunsogo and Padayachee (2002), the reduction in durability
and performance presented by recycled concrete occurs due to the cracks
in the aggregates created during the recycling process, which becomes an
easy way for the passage of fluids and aggressive components besides the
presence of a more porous structure. Nevertheless, it is known that if recycled
concretes have a good new mortar this will prevent the passage of deleterious
agents, preventing them from reaching the recycled aggregates.
If we compare concrete within the same range of compressive strength,
it appears that recycled concretes are more resistant to the penetration of
chlorides and CO
2
. This behavior can be explained by the reduction of water/
cement ratio by the recycled concrete in order to achieve the same strength
of conventional concrete. This particular reduction causes a substantial
improvement in the cement matrix, making it less permeable, thereby
impeding the penetration of aggressive agents (Dhir et al., 2004a).
levy (2001) concluded that the carbonation and chloride penetration in
recycled aggregate concrete are much more connected to the water/cement
ratio and cement content, than to the type of recycled aggregate duly used.
Consistent with this, Otsuki and Miyazato (2000) state that these two properties
are more related to the quality of the ITZ in concrete, regardless of whether
the aggregate used is recycled or not.
Therefore, comparing low resistance and the same water/cement ratio
conventional concrete with recycled aggregate concrete, the recycled concrete
would be expected to have a worse performance, since both the matrix and
the recycled aggregate will be porous, allowing the penetration of aggressive
agents, while the natural aggregate is less permeable than the recycled,
thus hindering the penetration of aggressive agents. On the flip side, when
comparing conventional concrete with recycled aggregate concrete in high
strength with the same water/cement ratio, we expect the behavior of both to
be similar, since the matrix will be so little permeable that it will not allow
the penetration of aggressive agents.
14.5 Future trends
Further investigations about recycled aggregate concrete are being made
worldwide, researching about:
∑ self-compacted concrete with recycled aggregates - the content of ultra-
fines (<0.075 mm) produced in the CDW recycling is high and it can be
used in SCC;
∑ structural lightweight recycled aggregate concrete - recycled concrete
usually has an specific gravity lower than conventional concrete but it
is laborious to reach structural strength in lightweight concretes;
∑ reinforced fiber recycled aggregate concrete - the use of fibers in
