Page 252 - New Trends in Eco efficient and Recycled Concrete

220 New Trends in Eco-efficient and Recycled Concrete

highest impact on the recycled concrete mix design, because its influence on the
workability of the fresh concrete, and the performance of the recycled concrete
once hardened. However, the differential performance level shall not definitively
exclude the use of these materials. On the contrary, a more specific and case by
case study should be carried out in order to assess their quality in the framework of
a specific application.
Numerous researchers have investigated the possibilities of using recycled con-
crete aggregates (RCAs) (Bezerra-Cabral et al., 2010; Fathifazl et al., 2011;
Ferreira et al., 2011; Gokce et al., 2011; Go ´mez-Sobero ´n, 2002; Ismail and Ramli,
2013, 2014; Limbachiya et al., 2000; Lin et al., 2004; Manzi et al., 2013; Mazzotti
et al., 2013; Safiuddin et al., 2013; Soares et al., 2014; Tabsh and Abdelfatah,
2009), since their properties are the most similar to those of virgin materials and
most countries have specifications allowing and regulating their use. Although
more challenging in terms of mechanical properties, mixed recycled aggregates
have also been proven suitable for concrete manufacturing (Agrela et al., 2011;
Mas et al., 2012a,b; Mas-Gracia and Cladera-Bohigas, 2009; Medina et al., 2014;
Rodrı ´guez-Robles et al., 2015). Finally, in a more limited manner, ceramic recycled
aggregates from CDW have been used as well to improve the sustainability of con-
crete (Correia et al., 2006; de Brito et al., 2005; Gomes and de Brito, 2009;
Pacheco-Torgal and Jalali, 2010a,b; Sadek and El Nouhy, 2014; Yang et al., 2011).
In spite of studies supporting the use of these alternative sources, nowadays,
recycled aggregates only cover a 8% of the total production, while the remaining
aggregates come from pits (41%), or quarries (47%), alternatively they are manu-
factured artificially or they are sea dredged (4%) (UEPG, 2017). However, there is
a great potential for environmental alleviation through the reutilisation of the
recycled materials. Each tonne of recycled aggregates derived from CDW will dis-
place not only an equivalent amount of natural aggregates but its whole embodied
industrial and transport process, that is, avoided primary energy consumption and
implied CO 2-eq emissions (Coelho and de Brito, 2013). Moreover, each tonne of
recycled aggregates derived will avoid the landfilling and transport process of an
equivalent amount of CDW. In addition, as part of the CDW management process,
other materials, predominantly metal scraps, would be recovered and valorised.
A final benefit could be achieved by means of the CO 2 sequestration of the con-
crete fraction within the CDW. It is well known that a concrete structure exposed to
the atmospheric conditions will carbonate. The CO 2 in the air combines with the
free water in the concrete porous network to produce carbonic acid that reacts with
portlandite to create calcium carbonate (Heiyantuduwa et al., 2006). During storage,
the CO 2 absorbed by the crushed concrete in the CDW is higher than that during
the life span of the structure since the area of exposure is increased and there is
fresh uncarbonated concrete exposed to the environment. According to Collins
(2013), reductions up to 55% 65% of the kg CO 2-eq emitted by concrete produc-
tion could be achieved when the potential uptake of the recycled aggregate is con-
sidered previous to its new application. Due to the expected relative environmental
advantages, it has been proposed to force CO 2 sequestration of the RCAs by storing
them in a CO 2 rich environment (Tam et al., 2016; Zhan et al., 2014) or turning