Page 294 - New Trends in Eco efficient and Recycled Concrete

258 New Trends in Eco-efficient and Recycled Concrete

2006; Marinkovi´ c et al., 2017). An environmental assessment of a full life cycle is
needed to provide an answer to the question: can recycling really decrease the envi-
ronmental burdens of concrete structures?

10.2 State-of-the-art

There are many methodologies for evaluating the environmental loads of processes
and products in the course of their life cycle, but the most acknowledged (and stan-
dardised) is a life cycle assessment (LCA). Almost exclusively, environmental
assessment of concrete in the previous research was performed by using LCAs in
comparative assessments of conventional or NA concrete (NAC) and RAC.
However, a variety of different choices is possible within the LCA frame,
depending on the goal and the scope of the study. For instance, different system
boundaries are possible, that is, cradle-to-gate or cradle-to-grave approach.
Different approaches to life cycle inventory (LCI) data modelling, that is, attribu-
tional (Weil et al., 2006; Marinkovi´ c et al., 2010, 2017; Jime ´nez et al., 2015; Fraj
and Idir, 2017; Kleijer et al., 2017) or consequential approach (Knoeri et al., 2013;
De Schepper et al., 2014; Turk et al., 2015) can be applied. Functional units (FU)
of various complexities were chosen, more or less successfully. On the material
level, various compositions of RAC were analysed, with different replacement
ratios of NA with RCA which ranged from 30% (Turk et al., 2015), 45% (Knoeri
et al., 2013) to 100% (Marinkovi´ cetal., 2010, 2017).
Results and conclusions of the previous research vary a lot, from no or low bene-
fits (Fraj and Idir, 2017; Kleijer et al., 2017; Marinkovi´ cet al.,2017) to substantial
reductions of the environmental impacts in the RAC case (Knoeri et al., 2013). The
reason for this situation is twofold. Firstly, case studies are commonly based on the
geographically dependable data such as energy sources and supply types, transpor-
tation types and distances, production technologies and raw material types, etc.
Secondly, the results of comparative LCA depend on the methodological issues
being analysed, mostly on the FU selection and on the approach to LCI data
modelling.

10.3 Modelling in comparative LCA of concrete

In this chapter the most influential factors in comparative LCA modelling are dis-
cussed: selection of the FU and inventory data modelling, that is, choice of system
boundaries and influence of CO 2 uptake on the assessment results.

10.3.1 Selection of the functional unit

The four main aspects of any concrete structure’s function are strength, serviceability
(cracks and deformations), durability (i.e., duration of service life) and fire resistance