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Life cycle assessment applied to recycled aggregate concrete 219

9.2.2 Concrete sustainability through recycled aggregates

Traditionally, natural resources and waste are found, respectively, at the start and
ending point of the linear model of production, that is, the material life cycle, which
encourages the take-use-dispose attitude responsible for the problems in the first
place. Hence, the European Union has proposed to adopt a circular economy model
in order to transform the production chains and consumption habits by means of
turning waste into resources in order to close the production loop (European
Commission, 2014). Under this circularity principle, the resources stay within the
limits of the economy during several life cycles since they can be repetitively used
at the end of each life span. Then, the overall balance is the use of fewer natural
resources to produce the same output, which is the core of resource efficiency, and
a disruption in the relationship between raw material use and economic output, a
practice also known as decoupling (Van Ewijk and Stegemann, 2014).
Given the level of consumption and wastage, the idea of closing the production
loops is particularly useful among construction activities to alleviate their pressure
on the carrying capacity of the environment and contribute to a more sustainable
future. Nowadays, the scientific efforts are focused on proving the feasibility of
recycled aggregates as substitutes for the natural coarse aggregates in the produc-
tion of concrete in order to bolster this type of application. Fig. 9.2 gives an over-
view of common processing steps needed to obtain recycled aggregates from
concrete waste (Wang et al., 2018; Hiete, 2013).
The characteristics of the aggregates used in the manufacture of concrete largely
determine the properties of the final product. General knowledge indicates that
recycled aggregates present a lower quality than natural aggregates. A great com-
prehensive review on the differential properties of the recycled aggregates can be
found in Silva et al. (2014). Among the differences between the properties of the
natural and recycled aggregates, the water absorption is the parameter that has the

Waste treatment plant

Remove ferrous
Pre-sieving
metals using magnets
Waste generated on
site
Primary crushing Screening process to
using equipment such achieve desired
as pneumatic hammer classes
On-site sorting and Concrete waste Recycled aggregates
pre-treatment
Sorting, either
Control sieving to
manually or through
separate larger parts
mechanical equipment
Secondary crushing
using equipment such Further sieving and
mixing
as rotating crusher
Figure 9.2 A simplified processing map for the recycling of aggregates from concrete waste
as compiled by Hiete, 2013 and cited by Wang et al., 2018.