The role of service life in Life Cycle Assessment of concrete structures

Abstract

In comparative Life Cycle Assessment (LCA) of concrete structures it is of crucial importance to provide the functional equivalence of compared alternatives. Most commonly, the comparison is performed between the structures made of conventional and green concrete mixtures. Since they have different mechanical and durability properties, corresponding structures have different strength and service life. While resolving this problem, two approaches are generally possible: either correction of the functional unit volume or correction of the calculated environmental impacts with compressive strength and duration of service life, if functional unit has the same volume. In this work, in order to assess the effect of service life modeling in LCA, both approaches were tested. As a demonstration, comparison of both slabs and beams made of conventional and high volume fly ash concrete exposed to carbonation was carried out. LCA was performed for 94 different mixtures from reported experimental research and calculated environmental impacts (climate change, acidification, eutrophication, photochemical-oxidant creation, and abiotic depletion of fossil fuels) for both approaches were compared. Results showed that different modeling of service life in LCA can result in totally different, even opposite conclusions. With slightly larger volume of functional unit (7%–20%), all normalized environmental impacts of high volume fly ash concrete structural members were lower for an order of magnitude (6–7 times) compared to those obtained on the basis of the same volume approach. Therefore, drawing conclusions only on the basis of service life modeling with the same volume approach may be misleading. The proper choice of the best alternative should be based on the integrated assessment which includes structural, environmental and cost assessment of the structure as a whole.