Page 279 - New Trends in Eco efficient and Recycled Concrete

Life cycle assessment applied to recycled aggregate concrete 243

Nowadays, cradle-to-gate approaches are mostly used in related LCA literature.
However, it has been argued that the inclusion of the subsequent construction
phases could have an influence on the final results. Furthermore, since the use of
recycled aggregates is in agreement with the circularity principle proposed by the
European Union, a cradle-to-cradle approach seems the most accurate representa-
tion of the real scenario. However, to date, closed-loop LCA studies are minority.
On this note, Marie and Quiasrawi (2012) proposed the need to evaluate the techni-
cal behaviour and environmental impacts occurring from the subsequent recycling,
that is, the use of recycled aggregate of a structure already made from recycled con-
crete, to favour closing the recycling loops as well as the construction loops to cap-
ture the opportunity for sustainability in terms of avoided landfilling and unlimited
consumption of natural aggregates.
Some clear differences could be encountered between LCA studies applying
attributional and consequential modelling to assess the environmental profile of the
recycled aggregate; the latter being generally more beneficial. However, in the
assessment of the environmental burden of construction materials, it has been found
that both modelling approaches give comparable results (Santos Vieira and
Horvath, 2008). Therefore, LCA papers in which no attention is payed to natural
resource conservation, reuse of scrap recovery from CDW, avoidance of landfilling
(land use and net transport difference between recycling plant and landfill), etc., are
not truly including the beneficial environmental aspects of the second life of
recycled aggregates regardless of whether allocation or substitution methods are
applied. In any case, it must always be accepted that conclusions arising from LCA
are dependent on the scenarios and modelling approaches proposed. As a conse-
quence, they must not be extrapolated universally.
In terms of LCI, despite resorting to databases for most of the products and pro-
cesses, those related to the CDW or recycled aggregates should be created by the
user from actual site data. Although, to date, CDW is legally a waste according to
Directive 2008/98/EC (European Union, 2008) and, as such, has a zero burden input
(which means that. no past energetic-environmental burdens are assigned to it), the
recycling process entails an important energy consumption and its implications
should be considered in the LCA framework. Within the impact assessment phase,
the impact categories included in LCA interpretation methods such as Eco-indicator
99 and CML 2002 are widely used, but some researches also include their own
indexes related to landfill use, solid waste generation or resource depletion to
account for the environmental credits included in the life cycle of the recycled
concrete.
Regarding the interpretation of the LCA results, a consensus exists about the
need for sensitivity analysis as a means to define the conditions under which a
recycled concrete mixture is environmentally favourable or unfavourable compared
to the conventional concrete. Transport is regarded as the most common variable
influencing the environmental performance of the recycled concrete and conse-
quently distance limits have been proposed for the haulage of the CDW, recycled
aggregates or recycled concrete in order to remain environmentally sustainable.
Besides transport, CDW composition, quality or management, type of aggregate