Page 266 - New Trends in Eco efficient and Recycled Concrete

234 New Trends in Eco-efficient and Recycled Concrete

According to Benetto et al. (2004) the problem related approach provides reli-
able results, although it is sometimes difficult to compare them with each other.
Damage-oriented impact analysis allows for a much easier interpretation of the
LCA output, but is considered to be not so reliable.
Specifically in view of LCA of concrete with recycled aggregates, choosing an
appropriate impact method is not that straightforward. Most of impact analysis
methods (e.g., Eco-indicator 99 and CML 2002) do not include impact categories
accounting for the waste production and mineral resource depletion, which are two
of the major impacts of conventional concrete that could be alleviated by the use of
recycled aggregates. Neither the natural aggregates supply or the landfill capacities
are limitless and thus their consumption should be considered as a negative impact
at the same level as any nonrenewable resource consumption. Since resource con-
servation and wastage avoidance are pivotal points in the comparative environmen-
tal impact between natural and recycled aggregates, indexes representing this topic
in the LCA approach should be included in order to improve the final interpretation.
Thus, some researchers have constructed and included their own indicators regard-
ing to the amount of waste produced and/or depletion of natural mineral resources
(Colangelo et al., 2018; Habert et al., 2010; Marinkovi´ c et al., 2010; Simion et al.,
2013; Toˇ si´ c et al., 2015) in order to take into account such impacts.

9.3.4 Interpretation

One of the key parts of the interpretation phase is the identification of the signifi-
cant issues based on the results of the LCI and LCIA phases. Key literature findings
in that perspective for concrete with recycled aggregates have been summarised in
this section.
According to Weil et al. (2006), the energy consumption and global warming
potential of conventional and recycled concrete (35% and 50% substitutions) are
comparable if no additional cement is used, since the cement production contributes
between 75% and 94% in all impact categories. When additional amounts of
cements were employed, the cumulative energy demand and the global warming
potential increased by 36% and 39% compared to conventional concrete. In line
with that, Braga et al. (2017), carried out a literature review (216 concrete mixes
from 24 studies), and observed a strong correlation between the global warming
potential and the cement content regardless of the type of aggregate (natural or
recycled). Similar results were found for the consumption of primary nonrenewable
energy, which increases with the cement content independently of the concrete
class. The same authors suggested that the use of superplasticiser is more sustain-
able than the incorporation of additional cement to overcome the shortcomings of
the recycled aggregates. Nevertheless, irrespective of the cement content, the incor-
poration of coarse recycled aggregates improves the environmental performance of
recycled concrete for all categories (with exception of the abiotic depletion poten-
tial, due to some statistical limitations).
Since the environmental performance of concrete made with recycled aggregate
is dependent on the variation of some conditions, the majority of the studies include