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Life cycle assessment applied to recycled aggregate concrete 215

(Hardening) accelerators are aluminium sulphate, formates, fluorides, aluminates, amor-
phous aluminium hydroxide, carbonates, silicates and ethanolamines, as well as, nitrates,
nitrites and thiocyanates (EFCA, 2015b).
Plasticisers and superplasticisers are comprised of ether lignosulphonate, naphthalene sul-
phonate, melamine sulphonate and polycarboxylate/polycarboxylic ethers or mixtures
thereof (EFCA, 2015c).
Retarders can include sucrose, gluconates, phosphates, and lignin sulphonates (EFCA,
2015d).
For water-resistant admixtures, primarily salts or dispersions of higher fatty acids as well
as emulsions containing silanes or siloxanes as active agents are used in conjunction with
defoaming and emulsifying agents (EFCA, 2015e).
These EDPs provide information regarding the raw materials, emissions to air,
emissions to soil and emissions to water associated with the respective admixture.
It is worth mentioning that the information corresponds to the worst-case scenario,
that is, the product with the highest environmental impact.
All admixtures affect predominantly the global warming potential category, with
values ranging from 527 to 2280 g CO 2-eq /kg for air entrainers and hardening accel-
erators, respectively, followed by its acidification potential of land and water, which
means emission between 1.30 and 10.40 SO 2-eq /kg for air entrainers and retarders,
respectively. Emissions responsible for eutrophication and photochemical oxidants
amounted 0.14 1.54 g (PO 4 ) 32 Eq /kg and 0.31 0.96 g Sb -eq /kg. The impacts on the
ozone layer and nonfossil resources depletion potential categories were negligible
(,0.1 g/kg). In terms of fossil resources depletion, consumptions of around
13.30 51.00 MJ/kg were reported. The overall low impacts together with the small
amounts used in concrete, downplay the contribution of admixtures in the environ-
mental profile of concrete. Nevertheless, although admixtures are firmly bound into
the cement matrix during the use phase, impacts could be produced at the end-of-
life scenarios, so leaching of harmful substances from concrete demolition waste
should be assessed.

9.2.1.4 Aggregates
According to Krausmann et al. (2009), around 47 59 billion tonnes of materials
are mined annually. Since concrete is the most-used building material in the world,
the consumption of sand and gravel, which represent around an 80% by mass in
concrete, accounts for the largest volume of solid material extracted worldwide.
The European Aggregates Association reported that the annual demand of aggre-
gates in the European Union equals up to 2.70 billion tonnes, of which 25% are
required by the ready-mix concrete industry and 20% are destined for precast con-
crete and architectural concrete products (UEPG, 2017).
Despite being aware of the limited nature of natural resources such as sand and
gravel, their consumption answers to the belief of an almost limitless supply at
worldwide level. According to Habert et al. (2010), the depletion of bulk resources
is different depending on the size of the territory of study. While at world scale
depletion of resources could be assumed trivial, at local scale the depletion is clear