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Life cycle assessment applied to recycled aggregate concrete 217

equipment, emission control systems and for preparing slurry in wet process kilns.
Moreover, the production of aggregates entails important water consumption when
wet screening and washing procedures are included. It is estimated that to produce
a tonne of natural aggregates 1000 L of water are needed (Kellenberger et al.,
2007). Finally, the manufacturing of concrete also necessitates water for the produc-
tion (hydration process) and curing and cleaning processes. For example, it has
3
been reported that 65 L/m are used in ready mixed concrete production excluding
3
the batch water (Marceau et al., 2007) and around 567 L/m of water are used for
cleaning purposes (Turk et al., 2015). These demands represent a high depletion
potential of surface and groundwater resources; thus, these industries are trying to
get rid of the negative environmental impacts associated to the water consumption
by using harvested rainwater and recycled water from manufacturing processes.
Impacts induced by concrete related water consumption are not considered
within the LCA framework, but can be accessed via the determination of its water
footprint (WF). According to Hoekstra et al. (2011) a product WF comprises the
amount of water that is consumed and polluted in all processing stages of its pro-
duction; hence, WF encompasses a direct and an indirect component, and it is mea-
sured in water volume per unit of production. However, there is no correlation
between a WF and potential environmental harm (Ridoutt and Pfister, 2010).

9.2.1.6 Energy
During concrete production, the energy consumed from the mining and processing
of natural resources up until the actual manufacturing stage is commonly defined as
the embodied energy, and has been estimated between 0.89 (Struble and Godfrey,
2004) and 1.40 MJ/kg (Alcorn and Baird, 1996). Moreover, the embodied energy of
reinforced concrete increases up to a 63% (Zabalza Bribia ´n et al., 2011) because
the energy inherent to the production of steel rebars should be added.
Aggregates only account for 17% 25% of the embodied energy of concrete
(O’Brien et al., 2009). Mah et al. (2017), who recovered industrial information, stat-
ing that the mining (diesel powered) of 1 t of natural aggregates consumed
10.75 kW h and its subsequent management (several stages of screening and crush-
ing electricity powered) resulted in an additional consumption of 3.31 kW h/t.
Nonetheless, it is recognised that most of the embodied energy of concrete is
used in the cement production for crushing, grinding, rotating the kiln, etc.
Annually, at a European cement plant, the power consumption and the required
thermal energy were, on average, 117 kW h/t of cement and 3.75 MJ/t of clinker,
respectively (WBCSD/CSI, 2013). According to Taylor et al. (2006), these
figures could be reduced if supplementary cementitious materials, dry processes
and pre-calcination techniques would be used. For instance, the use of blast-furnace
slag could produce energy savings ranging from 21.10% to 48.40% (Prusinski
et al., 2004). In addition, the impacts associated with the energy demand in the
cement production could be reduced by the use of alternative fuels, since the envi-
ronmental impacts caused by energy consumption depend on the type of energy