Page 339 - New Trends in Eco efficient and Recycled Concrete

296 New Trends in Eco-efficient and Recycled Concrete

11.2.3 Integration of these concepts in an LCA

The application of a detailed LCA approach to construction works is a complex,
onerous and extensive task because of the quantity of products and processes
included in this industry, the long life cycle of these products when finished, the
different service life of the components of the building and the dynamic that differ-
entiates buildings from other standard industrial products, namely during execution,
use and end-of-life phases (Blok et al., 2007; Chevalier and LeTeno, 1996; Kibert,
2002). The application of the LCA approach in its purer form to this industry is
also difficult because of the quantity of data concerning its processes. This makes
the definition of a declared or functional unit (which is a service and not only a
product) to be used even more important, in order to lessen the sensitivity and
errors of the results (Erlandsson and Borg, 2003; Ozik, 2006).
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Examples of declared units used in LCA studies are: 1 kg of cement; 1 m of
ready-mixed concrete; one brick or one window. On the other hand, a functional
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unit of a construction material can be: 1 m of a ceramic cladding for a specific use
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during 50 years; 1 m of brick with a given thermal resistance RD (m K/W) during
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50 years; 1 m of ready-mixed concrete with a given compressive strength at 28
days during 50 years.
11.2.4 Ways of defining equivalent functional units
The functional unit should be defined based on ‘the way in which the identified
functions or performance characteristics of the product are quantified...‘when inte-
grated into a building’ and on the product’s or building’s service life (CEN, 2013).
Considering the geometry of the product when integrated in the building, a ‘unit’ is
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first defined, such as ‘1 m of insulation board’, ‘1 m of ready-mixed concrete’,
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‘one window’, ‘1 m of brick wall’, or ‘1 m of plastic pipe’. Then, one or more
functions of the material must be selected in order to make this ‘unit functional’,
and to provide a reference flow for meaningful comparisons between functionally
equivalent alternatives. In that sense, technical characteristics, including durability,
are usually selected to define the functional unit of a construction material for com-
parison purposes. For a ceramic cladding, for example, a specific use and service
life is usually defined, such as ‘applied in the floor of an apartment for 50-years’,
in order to express the wear conditions. For an external wall, where the thermal per-
formance is an important dimension of performance, one may choose the guarantee
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of ‘a given thermal resistance RD (m K/W) during 50 years’ as the adequate func-
tional unit to be considered to compare alternative solutions.

11.2.5 Application to concrete
If one focuses on concrete as a case study, the definition of a functional unit as
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‘1 m of ready-mixed concrete with a given compressive strength at 28 days endur-
ing 50 years’ can be interpreted and implemented in many ways, since strength and
durability requirements are considered simultaneously. First, it is important to