Page 268 - New Trends in Eco efficient and Recycled Concrete

236 New Trends in Eco-efficient and Recycled Concrete

the influence of the need for modifications in the fabrication process or changes in
the mix design. The authors stated that the higher embodied energy due to the
increased cement content were the overall responsible for the differences in the
environmental profile of natural and recycled concretes and proposed the use of
secondary cementitious materials as supplementary binder due to their lower effect
on the embodied energy of concrete. Later on, in another LCA carried by
Marinkovi´ c et al. (2017), recycled concrete performed poorly for every scenario
compared to conventional concrete due to the higher cement content used in the
recycled mixtures. For that reason, the authors recommended an adjustment of the
water cement ratio and the use of superplasticisers to obtain a better environmental
performance. In addition, a study regarding the influence of the mix design in the
LCA results of recycled concrete could be observed in Jime ´nez et al. (2015). The
authors proposed the equivalent mortar method (Fathifazl et al., 2009), which could
maintain a good long-term behaviour of recycled concrete under smaller cement
quantities although requiring greater amount of admixtures, as a means to accom-
plish better environmental performance than the conventional concrete and the con-
ventional methods (ACI and Bolomey) for designing recycled concrete.
In Slovenia, Turk et al. (2015) studied the environmental impacts caused by
green concretes made from concrete waste by means of a consequential LCA, in
which the avoided landfilling and material recovery were treated as environmental
credits. The authors observed that recycled concrete in a mobile plant decreased the
photochemical ozone creation potential by 20%, and the abiotic depletion, acidifica-
tion and eutrophication potential, cumulative energy demand and global warming
potential by 10%, when transport distances were not considered. However, the envi-
ronmental advantages disappeared for transport distances over 100 km (one-way
trip). The choice between using a stationary or mobile CDW management plant as
supply source is not always clear. A sensitivity analysis needs to be done since the
implied burden within the recycling process could vary significantly. For instance,
Lo ´pez Gayarre et al. (2016) studied the life cycle of precast kerbs made with
recycled aggregates from stationary and mobile management plants. For a 50% sub-
stitution of recycled aggregates produced in a fixed plant, both energy consumption
(15.8%) and environmental performance (167.3 t/year) got worse in comparison
with conventional concrete. These values increased even more when the recycled
aggregates were derived from a mobile plant since it was mandatory to move the
mobile sieve and grinding installation to the building, which results in a 30%
increase in energy consumption in comparison with a fixed plant for the processing
of the CDW. Moreover, Wijayasundara et al. (2017) reported variations of
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4766 5401 MJ/m within the embodied energy of concrete containing several
replacement ratios and types of recycled aggregates depending on the feeding and
storage mechanisms available at the management plant, which clearly influenced
the comparative performance against a conventional concrete (from 26.8% to
111.4%).
Estanqueiro et al. (2018) showed that the use of recycled coarse aggregates (pro-
duced in a stationary or mobile plant) did not have a positive environmental score
compared to the use of natural aggregates if the co-produced recycled fine