Page 317 - New Trends in Eco efficient and Recycled Concrete

276 New Trends in Eco-efficient and Recycled Concrete

(XC1 and XC3) and CO 2 uptake (taking it, or not taking it, into account). Two
approaches for LCI modelling were tested: attributional and consequential.
In order to provide functional equivalence, reference flows in each studied alter-
2
native were calculated for 1 m of the slab using the data in Table 10.6.
System boundaries were chosen in accordance with the LCI modelling approach
and shown in Fig. 10.2. Since the amount of concrete and reinforcement per FU
was different, all life cycle phases except the use phase were included in the assess-
ment. Use phase was considered to be similar in all cases based on the assumption
that maintenance, repair or replacement of the concrete structure was not going to
be needed in the course of the service life. Generally, energy use to operate building
technical systems and operational water used by them is not relevant for concrete
structure.
Recycling is a multifunctional process which supplies waste management for
upstream products and material for downstream products. Recycling of concrete
from one product life cycle (NAC) to another (RAC) is an example of open-loop
recycling. In the attributional approach inputs and outputs of recycling process are
allocated between these products. Although there are more refined approaches
(Allacker et al., 2014), a relatively simple but not uncommon cut-off rule was
adopted in this study (Vogtl¨ ander et al., 2001): demolition (including transportation)
was allocated to the NAC life cycle, while the recycling process itself was allocated
to the RAC life cycle, Fig. 10.2. As a result of the recycling process, two co-
products are obtained; RCA and iron scrap, and inputs and outputs of the recycling
process were allocated between them. If the amount of steel in RC is on average
3% (w/w) (Doka, 2009), iron scrap content of 2% (w/w) for concrete waste mixed
from plain and RC can be assumed (Knoeri et al., 2013). Taking into account the
cost of RCA and iron scrap in Serbia ( Є 12 per tonne of RCA and Є 0.8 per kilo-
gram of iron scrap) it was calculated that the difference in revenue from these co-
products was less than 25%, in which case mass allocation should be applied (CEN/
TC229/WG5-N012, 2016). Since the mass (weight) of iron scrap was only 2%, all
impacts of recycling were allocated to RCA, that is, RAC life cycle.
In the consequential approach, the recycling process was ascribed fully to RCA
production (RAC life cycle), and RCA production was credited for the processes
that were displaced by recycling: waste landfilling and pig-iron production,
Fig. 10.2. However, the assumption was made that iron scrap was fully utilised in
steel making processes and actually displaced pig iron there, and that there were no
differences between them (substitution 1:1).
Recycling process consists of demolition, transport to the recycling plant and
recycling plant operation. In this study, recycling was performed in a mobile recy-
cling plant at the demolition site since there were no stationary recycling plants in
Serbia. So, transport of a mobile recycling plant to the demolition site was included
instead of transport of waste from demolition site to recycling plant. For each cam-
paign of 2500 t the mobile plant (20 t) is transported at a distance of 100 km.
Landfilling of the recycling waste which cannot be used as RCA (assumed recovery
rate equal to 60%) was also included in the recycling process in this study.