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Equivalent functional unit in recycled aggregate concrete 313

1.400

1.300
K-value 1.200

1.100

1.000
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
RAC mixes
Figure 11.8 Range of the K-value for slabs.

RAC (lower thickness of the slab) would still comply with the checked limit states.
However, an outlier analysis proves that the method leads to oversized slab heights
only for cases where there is a combination of low quality RA, high replacement
ratios and severe environment situations.
The feasibility of all these cases is considered by using the K-values. The RAC
mixes that have higher K-values may be excluded from design situations because
the advantages of using RAC may be offset by the disadvantage of having to use
much more material and increasing the dead weight of the structure, affecting also
its dynamic and seismic behaviour (due to their higher mass). The replacement ratio
and the quality of the aggregates of the 32 slabs is checked whether they have high-
er values of the EFU than those expected. Table 11.5 demonstrates that the higher
K-values almost always correspond to a replacement ratio of 100%, with the excep-
tion of C¸ akır (2014).
The same method has been extrapolated for beams with acceptable results.
Dobbelaere et al. (2016) used the same approach to test 29 different beams and con-
cluded that the K-values range from 1.0 to 1.3 (Fig. 11.9), and:
13 examples have a K-value below 1.1;
5 examples range from 1.1 to 1.2;
11 examples range from 1.2 to 1.3.

11.7.3 Exclusions and limitations

Even though the method has been validated, there are some limitations to its use
that must be emphasised. First, the method has been developed for solid slabs and
beams of limited span, not being confirmed for other structural elements (e.g., waf-
fle slabs, columns and foundations) or larger spans. Limitations regarding other
environmental conditions must also be considered, as freeze-thaw and chemical
attacks were not considered. Finally, the method was tested for concrete strength
classes from C20/25 to C50/60, meaning that for higher concrete classes the results
shown may not be valid.
Regarding other structural elements, such as columns, the method is not valid
due to the complexity of the computations. The ULS for columns must include