The influence of the Functional Unit on the comparability of life cycle assessments in the construction sector: A Systematic Literature Review and attempt at unification for Reinforced Concrete

This article explores the potential for unifying Functional Units (FU) for all LCAs in any given product category in the construction sector. To this end, a Systematic Literature Review (SR) has been conducted. Due to the significant environmental impact of Reinforced Concrete (RC) and its ubiquitous global utilization, it is taken as an exemplary model for a unified FU.. The results of this SR show a significant heterogeneity in the choice and definition of FUs in the construction sector. FUs were extracted from the source material and categorized by the authors into five primary categories. The literature review found Reference Flows (RF) to be the most commonly named type of FU (75%), although FU and RF are not defined in the same way according to the LCA norm. The authors suggest a feasible standardized FU for RC structures. FUs for RC must include Reference Service Life (RSL), strength requirements, durability, and basic material specifications to achieve reasonable functional equivalence. Given the context of LCA as a support to decision-makers (DM), a standardized property FU for RC is most appropriate. This might be defined as 1 m3 of concrete normalized by the 28-day compressive strength and the RSL, including exposure class, specific concrete, and type and percentage of reinforcement. Lastly, the authors argue that a standardized FU is not enough to produce reliable and comparable LCA results. Data limitations, methodological issues, and a questionable practicality of implementation must also be addressed. Short-, mid-, and long-term measures to this end are suggested.