Page 260 - New Trends in Eco efficient and Recycled Concrete

228 New Trends in Eco-efficient and Recycled Concrete

Just like Van den Heede and De Belie (2012), Panesar et al. (2017) proposed a
classification system for the different FUs specified in literature. According to the
latter, FUs could be classified as simple (single variable, commonly mass or vol-
ume), moderately complex (two variables) and complex (three or more variables).
Some of the most employed variables were volume of concrete, mass of cement,
volume of aggregate, compressive strength of concrete, service life, binder intensity
and CO 2 content. The authors suggested the need for functional units relating to
metrics of concrete regarding to its application and exposure conditions. This obvi-
ously also goes for concrete with recycled aggregates.
On the one hand, it has been proposed that when conventional and recycled con-
crete are designed with the same target compressive strength and workability, both
mixes could satisfy the same strength and durability requirements for applications
under nonaggressive environment conditions, which is the basis for a comparative
environmental impact of different concrete types (Marinkovi´ c et al., 2010). Despite
durability been mentioned as a parameter to increase the comprehensiveness of the
functional unit (Panesar et al., 2017), the durability data regarding long-term behav-
iour of recycled concrete are still limited and mostly dedicated to the behaviour of
loaded beams (Choi and Yun, 2013; Knaack and Kurama, 2013); thus, it is difficult
to include as a metric within the LCA functional unit.
Dobbelaere et al. (2016) suggested a method based on a k-value or correction
factor to determine an equivalent functional unit for recycled concrete with respect
to the conventional concrete. The authors proposed that to achieve equivalent struc-
tural performance between conventional and recycled mixtures different volumes of
concrete should be used to account for the gains or losses in each property consid-
ered. For the same mixture and particular serviceability, the equivalent functional
unit would be greater for recycled concrete than conventional concrete but will
allow for a fair comparison between the different products. A similar approach was
previously proposed by Van den Heede and De Belie (2012), who established the
functional unit in such a way that impacts were assessed based on the total amount
of concrete needed to produce a specific structure with a specified mechanical per-
formance during its predefined service life.

9.3.1.2 System boundaries
Although the definition of LCA as specified in the ISO 14040 (2006); ISO 14044
(2006) standards suggests that the whole life cycle of a product/system should be
studied, this is not often done for concrete. Commonly, the systems boundaries of
the studies are limited to the production of the raw materials, the transport to the
manufacturing plant and the production of concrete, which constitutes a cradle-to-
gate LCA. Exclusion of the use and end-of-life phase can often simply be explained
by the fact that the necessary data to support such a full scale cradle-to-grave study
are often missing, and this especially for novel concrete types for which there is
limited experience beyond the production stage (Van den Heede, 2014). Some
examples of cradle-to-gate studies can be found in (Braga et al., 2017; Fraj and
Idir, 2017; Kurad et al., 2017). Nevertheless, due to the lack of data or their