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Comparative studies of the life cycle analysis between conventional and recycled aggregate concrete 259

(sometimes concrete members also have sound or thermal insulation function).
Neglecting of any of these in choosing the FU is not be an option, otherwise a com-
parative LCA cannot be done: why compare structures that cannot carry equal loads,
have different deflections under same load, cannot last for the same period of time or
endure the same fire load. In previous, more elaborate LCA comparative studies,
strength was usually modelled with sufficient accuracy, serviceability and fire resis-
tance were rarely modelled, while durability was often wrongly modelled.
Modelling of service life in the environmental assessment of concrete (structure)
has received a lot of attention in the research community. Although serviceability
and fire resistance are not less important structural functions, the FU of a type, that
is, unit volume of concrete per MPa of strength and per year of service life, is often
selected (De Schepper et al., 2014; Panesar et al., 2017). In other words, reference
flows are multiplied by ratios of strengths and service lives of compared alterna-
tives, where service lives are calculated on the basis of concrete carbonation or
chloride ingress resistance. At first glance, it looks logical and correct, but this is a
simple extrapolation of plain concrete performance to reinforced concrete (RC)
structures. Deterioration mechanisms which are commonly investigated (carbon-
ation or chloride induced reinforcement corrosion) affect only the service life of
RC structures and not the service life of plain concrete. For strength, such calcula-
tion is approximately correct (not for all stress states is there a linear relationship
between concrete compressive strength and volume of the member/structure), but
for durability this is completely wrong. This is because there is no linear relation-
ship between the whole chosen volume of the RC member and its service life, but
there is a certain, non-linear relationship between the depth of concrete cover and
duration of RC member service life, if the deterioration mechanism is reinforcement
corrosion. And this is not the same at all (Marinkovi´ c, 2017).
Therefore, one should calculate the amount of all reference flows needed for cer-
tain strength, serviceability, service life and fire resistance of compared RC struc-
tures. Or, in ISO 14041 terminology (ISO, 2006), all reference flows of compared
alternatives should be corrected for FU which reflects all relevant functional aspects
of the concrete structure. For that reason, general conclusions in the environmental
assessment of RC structures can hardly be drawn. Beside many other factors inherent
in the LCA modelling, they depend on the type (beam, slab, column, etc.) and size of
the RC member/structure and may differ in each specific case. One example of
defining a FU which takes into account the main aspects of the structural perfor-
mance is given in Dobbelaere et al. (2016). Based on the analysis of material proper-
ties, the authors showed that, depending on the particular serviceability and ultimate
limit state, equivalent FU was higher for RAC than for corresponding NAC.

10.3.2 System boundaries: attributional versus consequential
modelling

There are two different approaches to LCI data modelling: attributional life cycle
assessment (ALCA) and consequential life cycle assessment (CLCA). In