Page 255 - New Trends in Eco efficient and Recycled Concrete

Life cycle assessment applied to recycled aggregate concrete 223

By means of a hybrid LCA, Kucukvar et al. (2014) also analysed the same three
waste management options for different CDW fractions. Once again, recycling was
recognised as the better option for water, energy and carbon footprint reduction.
The results of Dahlbo et al. (2015) studying the potential climate change impacts of
CDW management by means of an LCA showed that the recycling had an overall
positive environmental effect, although the initial composition of the waste condi-
tioned the actual benefit. Similarly, mixed CDW were considered among the frac-
tions with a higher potential for reduction of climate change impacts.
In China, Wu et al. (2015) evaluated three end-of-life efficiency recovery scenar-
ios: (1) wood incineration, metal recovery and landfilling of the remaining materi-
als; (2) recycling of concrete, bricks, block and mortar, metal recovery and wood
incineration; and (3) complete CDW recycling. The carbon emissions decreased
accordingly with the number of scenario up to an almost 11% reduction for CDW
recycling. Mah et al. (2017), who also studied the greenhouse gas emissions per ton
of CDW managed or landfilled, affirmed that the crushing of CDW as recycled
aggregates to supply a concrete batching plant resulted in the most environmentally
positive alternative.
Moreover, a net assessment of the impacts generated by transport to the recy-
cling plants and the environmental credits gained by recycling could incur in
another trade-off. The transport distance and the value of the avoided impacts
would determine the friendliness of the management option. Therefore, transporta-
tion patterns are usually taken into account and even subject to a sensitivity analy-
sis. Blengini and Garbarino (2010) carried out a GIS analysis on the transport
distances linked to the CDW management and found that the haulage should experi-
ence a twofold or threefold increase before the CDW recycling would become unfa-
vourable. Ortiz et al. (2010) reported that in terms of global warming potential,
recycling and incineration continued to be the better alternatives even for increased
distances between the building site and the treatment plant (except for the stony
materials). The authors pointed out that the best management for stony materials
lies within on-site recycling to replace natural gravel, a conclusion that agrees with
the results of Hossain et al. (2017a). The study of Mah et al. (2017), who compared
the greenhouse gas emissions produced in the CDW management, showed a 9.8%
10.5% reduction when the mobile plant was within a 3 km radius from the construc-
tion site. Finally, Penteado and Rosado (2016) stated that, for a medium-sized city
in Brazil, the convenience of CDW recycling over landfilling was limited by a
30 km distance between the construction site and the recycling plant.
Since recycled aggregates are destined to replace natural aggregates, another
trade-off balance is established between the production life cycles of both materials.
This situation has also been subjected to investigation. Simion et al. (2013)
observed that CDW recycling produced about 40% of the impacts induced by natu-
ral aggregate quarrying. Moreover, the authors reported a seven times lower global
warming potential by the use of recycled aggregates instead of natural aggregates.
Similarly, Faleschini et al. (2016) indicated that natural aggregates were less
environmentally favourable than the recycled aggregates for all impact categories
regardless of their quality. Moreover, the authors affirmed the impacts caused by