ABSTRACT
ABSTRACT The purpose of this study is to evaluate the effects that the choice of functional unit has on the results of comparative life cycle assessments (LCA) for concrete. Three functional units were considered: volume, binder intensity with compressive strength as a performance indicator (BI-CS), and binder intensity with time to first repair (TFR) as the performance indicator (BI-TFR). To consider the effect of cement replacement, four mix designs with varying levels of cement replacement by fly ash (0%, 25%, 35%, and 50%) were compared using a cradle to grave comparative LCA analysis. A number of key outcomes were identified in the analysis. Firstly, when volume is used as the functional unit, the LCA results depend on the level of cement replacement and the cement content of the mix such that the higher the level of replacement, the lower the LCA results. Secondly, the LCA results were influenced by the level of cement replacement when BI-CS is used as the functional unit in that the higher the level of replacement, the lower the LCA results except for ecotoxicity and human toxicity non-cancer impact categories due to the increase in transportation flows. Finally the LCA results were influenced by the TFR of the concrete mix when BI-TFR was used as the functional unit revealing that the higher the TFR, the lower the LCA results. The choice of functional units can influence the results of a comparative LCA to the point that it changes the order of preference of concrete mix designs.
