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Equivalent functional unit in recycled aggregate concrete 301

volume than those of NAC. To consider the changes in performance of these mate-
rials, it is important to define an EFU which reflects the lower performance of RAC
over NAC. In this way, LCA comparisons become balanced and are adjusted to
consider the true size of the structural elements under study.

11.4.1 Properties to take into account

The definition of the EFU should consider a broad range of properties that define
the relative mechanical, durability and rheology performance of RAC over NAC.
The properties under consideration are the most relevant ones to design the ele-
ments in terms of ultimate limit state (ULS), serviceability limit state (SLS), for a
given service life, which is controlled by durability criteria. The design rules and
equations used in this study are in accordance to the European reinforced concrete
standard, Eurocode 2 (CEN, 2005).

11.4.1.1 Compressive strength (f cm )
Compressive strength is the most important hardened state property, as it relates to
every other mechanical property and is usually an indicator of the concrete’s dura-
bility. Being also the most tested property of concrete makes it easy to collect
diverse data, which can validate the method.

11.4.1.2 Modulus of elasticity E cm and tensile strength f ctm
The modulus of elasticity (E cm ), and tensile strength (f ctm ) are fundamental mechan-
ical properties of concrete. Even though both affect reinforced concrete perfor-
mance at different levels, it is consensual that these parameters affect
fundamentally the deformability and cracking of reinforced concrete structures,
respectively. The effective modulus of elasticity, E c,eff , includes the effect of creep
and is in the long-term more relevant than the secant modulus of elasticity, E cm .

11.4.1.3 Depths of carbonation and chloride penetration
Because RA’s porosity is larger than that of NA, the carbonation and chloride pene-
tration coefficients are normally higher for RAC. The carbonation depth (x)isa
function of the concrete age (t) and of the corresponding coefficient (K c ).
Consequently, for a given common target service life for RAC and NAC structures
(e.g., 50 years), carbonation coefficients can be omitted if the ratio between the car-
bonation depths in RAC and NAC is considered.
As for chloride penetration depth, it can be explained by Fick’s laws of diffu-
sion. Simply speaking, the chloride penetration depth is governed by the square
root of the diffusion coefficient (D) times the age of concrete (t), and a constant,
depending on the diffusion conditions. Therefore, assuming the same target life
conditions as those considered for carbonation, as well as the same diffusion condi-
tions for RAC and NAC, the diffusion factor can be left out as well, if the chloride