Sustainable Construction A Life Cycle Approach in Engineering

4 LIFE CYCLE INVENTORY
4.1 Methodology
LCA methodologies are described in a series of international standards (ISO 14040, ISO 14041
to ISO 14044) setting the rules for conducting LCA. The International Iron and steel institute
has been providing inventory for steel products, from cradle to gate of factory since 1995 (see
worldsteel.org, Curran et al. 2006). But at that time, scrap was considered as a raw material with
neither burden, nor credit though using secondary raw materials saves energy and reduces the
environmental impacts. Nowadays, industries have worked aggressively to influence the methodology
and include the end-of-life (EOL) treatment and recycling of steel (Amato et al. 1996,
IISI 2005 and 2008, Hiroyuki & Toshiyuki 2005, Birat et al. 2005, Eurofer 2007, Johnson et al.
2008). The principles are (1) steel is considered as a closed-loop material and the main steps of
its LCA are the manufacture, the use phase and the EOL treatment, (2) LCI data include the
manufacture and EOL steps, practitioners will have to add the use phase. The important parameters
of the study are (1) the recovery rate RR, the fraction of material that is recaptured after one
life cycle, it includes the pre-consumer scrap generated during the manufacturing process and
the EOL scrap (post-consumer scrap) and (2) the yield Y representing the ability of the secondary
process to convert scrap into steel. And thus, if X represents the LCI indicator,
X X prim
RR Y (X prim
X rec
) (1)
where X prim = LCI indicator for primary manufacture; X rec = LCI indicator for recycling
process. It is also demonstrated that equ. (1) is still applicable if recycling is considered an indefinite
number of times.
It was already indicated that stainless steel is recovered to more than 90% (see Table 1). It
should be noted that austenitics are separated from other families thanks to their non-magnetic
property, they are recycled as austenitics whereas ferritics can be recycled as stainless or carbon
steel.
4.2 Comparative graphs (credits to Dr. Lionel Aboussouan)
Figure 2. Demand in primary energy (divided in non renewable and renewable resources) for each grade.
Figure 2 presents the demand in primary energy for the production of 1 ton of cold-rolled coil
made of 304, 316 and 430 stainless steel. The 430 grade demands less energy than the other two
considered grades. In Figure 3, three different RR are considered for the same grade (304) demonstrating
the great influence of the recycling on the primary energy demand. The same chart
for each grade and each RR is provided if Figure 4, but the carbon dioxide emissions to air are
depicted.
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