Page 363 - New Trends in Eco efficient and Recycled Concrete

318 New Trends in Eco-efficient and Recycled Concrete

Toˇ si´ c et al. (2015) complemented the study of Marinkovi´ c et al. (2010) by
applying a normative multi-criteria optimisation method (VIKOR method) devel-
oped at the University of Belgrade, Faculty of Civil Engineering (Opricovic, 1998)
in order to find the optimal solution. They showed that replacing50% of coarse NA
with coarse RCA is the best solution in terms of EI and also from an economic
point of view. However, the results of the other studies (Marinkovi´ c et al., 2010;
Toˇ si´ c et al., 2015) showed that the EI slightly increase as the incorporation of RCA
grows, despite RCA having clear advantages in terms of mineral resources, environ-
mental load, depletion and waste production (Toˇ si´ c et al., 2015).
A recent PhD Thesis studied, from cradle to gate, the technical and environmen-
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tal performance of 1 m of concrete mixes made with high incorporation ratios of
fly ash (FA) and recycled concrete aggregates (RCA), individually and jointly, with
and without superplasticiser (SP) (Kurad et al., 2017). The w/b was calibrated in
order to maintain the slump approximately constant in all the mixes studied. It was
found that:
The optimum mixes in terms of strength and environmental impacts are the ones made
with incorporation of both RCA and FA rather than single incorporation;
The strength to GWP ratio of concrete mixes depends on the FA RCA incorporation
ratio rather than the content of the individual materials;
The Embodied Energy (EE) of concrete mixes significantly decreased with increasing
incorporation ratio of coarse RCA or FA. On the other hand, the changes in EE caused by
the incorporation of fine RCA or SP are small.

11.8.2 Comparison between RCA and NCA based on compressive
strength as functional unit

The ‘methodology for the definition of EFU for RA concrete’ was not yet used in
LCA studies, neither based only on the compressive strength nor generalised to all
other properties. Nevertheless, Braga et al. (2017) compared the environmental (and
economic) LCA of NAC and RAC mixes from previous studies, per strength class.
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The functional unit of this study was 1 m of ready-mixed NAC and RAC, consid-
ering its 28 days’ compressive strength. The life cycle stages considered are
detailed in Fig. 11.10:
Production/extraction of all raw materials needed for the production of each concrete
(A1);
Transportation of raw materials to the concrete plant (A2);
Concrete production at the plant (A3).

11.8.2.1 Life cycle inventory
All LCI data for coarse aggregates and crushed fine aggregate, CARC (coarse
aggregates recycled from concrete) and concrete production were collected from
Portuguese companies. Data for river fine aggregate were collected from
Marinkovi´ c et al. (2010). Cement data were obtained from Blengini (2006),ina
study based on the production of a Portuguese company.