Page 34 - New Trends in Eco efficient and Recycled Concrete

Construction and demolition waste 11

durability (Otsuki et al., 2003; Pedro et al., 2014, 2015; Gonza ´lez and Etxeberria,
2014). The quality of RA, apart from being influenced by the original material’s
strength, can be improved depending on the beneficiation process implemented.
Subjecting CDW to multiple crushing and contaminant-removal stages leads to
higher quality RA (i.e., higher density and lower water absorption). Concrete made
with RA obtained from high-quality beneficiation is likely to present enhanced
durability. Still, it was also reported that, regardless of the number of processing
stages, provided that RA present similar water absorption capacities, the resulting
RAC will probably present similar durability (Dosho, 2007; Silva et al., 2015d).
With elapsing curing time, RAC may progressively present a comparable perfor-
mance to that of control NAC mixes. In the study of Kou and Poon (2013), the authors
evaluated how RAC made with up to 100% coarse RCA and increasing fly ash content
would perform throughout a 10-year period. Fig. 1.6 presents the carbonation depth
and total charge passed of RAC exposed to an outdoor environment. After 10 years,
RAC mixes, with no additions and with 100% coarse RCA, showed only 10% higher
total charge passed and carbonation depths, in comparison to corresponding NAC
mixes. As expected, a decline in the resistance to carbonation was observed for mixes
with 55% fly ash content due to the combination of effects from the RA’s additional
porosity and that of the cementitious matrix as a result of the cement’s dilution.
Some discrepancies have been reported regarding the influence of RA on the
resistance to freezing and thawing of concrete. While some reported negligible
differences when compared to control NAC mixes (Merlet and Pimienta, 1993;

8000 30
28-day 1-year 10-year
28-day 1-year 10-year
7000 25
Total charge passed (Coulombs) 5000 20 Carbonation depth (mm)
6000

4000
15
3000
10
2000

1000 5
0 0

Figure 1.6 Total charge passed (lines) and carbonation depth (columns) of RAC with
increasing coarse RCA and fly ash content. RAC, Recycled aggregate concrete; RCA,
Recycled concrete aggregate.
Source: Adapted from Kou, S.C., Poon, C.S., 2013. Long-term mechanical and durability
properties of recycled aggregate concrete prepared with the incorporation of fly ash. Cem.
Concr. Compos. 37, 12 19.