Page 341 - New Trends in Eco efficient and Recycled Concrete

298 New Trends in Eco-efficient and Recycled Concrete

with no recycling potential. Among the full scope of CDW, concrete, mortar and
ceramics comprise the bulk volume of all deposits, corresponding to 60% 80% of
all CDW volume (Ma ´lia et al., 2013; EPA, 2016). With this in mind, worldwide
research has mainly focused on the use of these sorts of materials as NA replace-
ment in concrete, and the results have shown that RAs are suitable to replace their
natural counterparts, even though some compromises must be made, as the concrete
performance tends to decrease as the replacement ratio increases (Rao et al., 2007;
Li, 2008; McNeil and Kang, 2013; Behera et al., 2014; Evangelista and de Brito,
2014).
One of the main challenges that the construction sector faces in the use of RAs
is their heterogeneity. Unlike NAs, which have relatively stable properties, given
their mineralogical nature, RA’s properties depend not only on the CDW source,
but also on their processing and treatment at the recycling plant (Ulsen et al., 2010;
Florea and Brouwers, 2013; Pedro et al., 2014). These different processing techni-
ques change key properties such as density and water absorption, morphology,
microscopy and contaminants content, among others (Rodrigues et al., 2013; Ulsen
et al., 2013; Silva et al., 2014). Therefore, it is crucial to categorise RAs from
CDW not only by their constituents, but also by grading them in some fundamental,
yet easy-to-determine, properties.
To address the need to categorise RAs based on their performance, rather than
their constituents, Silva et al. (2014) consulted the properties of almost 600 differ-
ent RAs from a wide range of worldwide authors, establishing a correlation curve
between the RAs, oven-dried density and their water absorption, as seen in
Fig. 11.1. Based on this curve, and on the Los Angeles abrasion loss, the authors
managed to create a new categorisation for RAs (from A being the best-performing,
to D being the worst performing) that is independent of their mineralogical nature.
With this new classing system, it was possible to correlate the aggregates’ perfor-
mance to the concrete’s performance, as referred in the next sections.

Figure 11.1 Correlation between water absorption and oven-dried density of recycled
aggregates (Silva et al., 2014).