Page 270 - New Trends in Eco efficient and Recycled Concrete

238 New Trends in Eco-efficient and Recycled Concrete

43.84% decrease in depletion of primary mineral resources in comparison with
conventional concrete. Colangelo et al. (2018), who also based their analysis on
a closed-loop recycled scheme, stated that the best environmental performance
was obtained by a 100% replacement of recycled aggregates, when assuming
that at the end of life of a concrete structure 85% of the resulting CDW was
used as a partial replacement of natural aggregates, while the remaining 15%
was landfilled.
In summary to this review book chapter, a table has been compiled that includes
the key bibliographical references with specification of the relevant issues related
to LCA of concrete with recycled aggregates per reference, such as the geographic
area, LCA goal, aggregate type, functional unit, system boundaries, LCA type,
excluded aspects, LCI data, impact categories, the environmental benefit, and the
sensitivity for transport (Table 9.4). As such, the reader can quickly retrieve further
reading material on specific related subtopics.

9.4 Conclusions

It is widely recognised that cement is the largest contributor to all impacts in con-
crete manufacturing. Nevertheless, in spite of a lower contribution to the total
impact generated by concrete, fine and coarse aggregates represent up to 80% of its
mass, so any differential change in impact load between conventional and alterna-
tive aggregates could be significant enough to foster sustainability gain in the con-
crete sector. Therefore, a comparison between the ecological footprint of concrete
made with natural or recycled aggregates can show that when closing the construc-
tion loop net environmental improvements are obtained. Due to its normalised
framework, LCA is the preferred tool to assess the differential environmental per-
formance of conventional and recycled aggregate concrete mixtures.
However, some considerations should be taken into account when LCA is
applied to recycled aggregate concrete. Firstly, to allow a fair comparison between
the conventional and recycled concrete both should be evaluated under the same
premises. Therefore, both products should have the same function in terms of
strength, durability and serviceability. Thus, functional units should be chosen
accordingly. In this regard, attention should be paid to the chosen method to
achieve similar mechanical and durability performance for both mixtures. Since
cement is the major material responsible for the environmental impact of concrete,
the common practice to include an additional cement content is detrimental to the
environmental performance of recycled concrete. The use of superplasticisers or
secondary cementitious materials have been proposed as more environmentally
acceptable options. In addition, the limited information regarding the long-term
durability of recycled concrete has also been reported as a hindering factor in the
inclusion of this metric in the chosen functional unit.
Besides achieving functional equivalence, comparative LCA should not exclude
any stage that results in a favourable outcome for either concrete mixture.