Civil Engineering Reference
In-Depth Information
containing a high content of cement paste, will possibly suffer major drying
shrinkages.
14.4.9 Resistance to fire
When concrete is subjected to high temperatures such as fires, major changes
occur in its components, leading to reductions in the compressive strength
and modulus of deformation. The above modifications come from the loss
of free water and water gel, changes in the structure of hydrated cement as
well as great aggregate expansions, giving rise to internal tensions that may
even disrupt the concrete (Cánovas, 1998).
Surveys show that recycled ceramic aggregate concretes have a superior
performance to conventional concretes in relation to the loss of the compressive
strength after both being exposed to high temperatures (Khoury, 1996, and
Newman, 1946, both cited in Khalaf and DeVenny, 2004; Schulz and Hendricks,
1992). This may be explained because the recycled ceramic aggregate is
thermostable, in contrast to natural aggregates, such as limestone, which are
not. It occurs due to the ceramic's raw material characteristics: a fairly high
ability to retain heat, not spreading it, non-flammable and having refractory
properties, which means that it maintains its integrity and resistance to high
temperatures, in some cases approaching 1000 °C. As a consequence of this
behavior, recycled ceramic aggregate concretes have more protection against
heat, which means that they can maintain their structural integrity against fire
for a much longer period than conventional concrete (Khalaf and DeVenny,
2004). Therefore, recycled aggregate concrete that contain a certain amount
of recycled ceramic aggregate possibly will have a better performance than
conventional concrete when submitted to high temperatures.
14.4.10 Depth of carbonation and chloride penetration
Depth of carbonation and chloride penetration are two of the most vulnerable
aspects of introducing recycled aggregates into concrete production and
are explained, as for the other durability-related characteristics (e.g. water
absorption), by the greater porosity of recycled aggregates compared with
that of natural aggregates (Brito and Alves, 2010). Tests conducted by Katz
(2003) and Evangelista and Brito (2010) show that the depth of carbonation
in recycled aggregate concrete is 1.1 to 2.5 times the reference concrete
carbonation depth. Figures 14.6 and 14.7 compare the carbonation depth
in a reference concrete and a recycled aggregate concrete, respectively,
according to lovato et al. (2012).
ryu (2002) and Tu et al. (2006), investigating the penetration depth
of chloride ions in recycled concrete aggregate concrete, found that the
penetration depth of these concretes was higher than for concrete with natural
