Within the development process of a new potentially "green" concrete type, it is at all times imperative to analyze its expected environmental benefit. When following the Life Cycle Assessment (LCA) methodology cf. ISO 14040, small variances in the first three phases (definition of goal and scope, inventory analysis, impact analysis) may induce important differences in the environmental score eventually obtained in the interpretation phase. The selected functional unit within a LCA should include all relevant concrete aspects, being mainly its strength and durability. If the concrete requires regular repair or even full replacement, the impact of the necessary rehabilitation actions will add on to the impact of the original concrete amount needed to initially build the structure. Therefore, to assess the environmental benefit of a high-volume fly ash (HVFA) concrete functioning in a chloride containing environment, the time to chloride-induced depassivation of the reinforcing steel (relative to an appropriate reference concrete) has to be assessed first. This normally necessitates time-consuming natural diffusion tests, to be performed at multiple testing ages to include the effect of concrete ageing. Alternatively, the concrete could be subjected to accelerated diffusion tests involving immersion in a high concentration NaCl solution for a shorter time period (NT Build 443) or to non-steady state chloride migration tests (NT Build 492), and this again at multiple testing ages (e.g. 28 days, 91 days, 1 year). The obtained chloride diffusion or migration coefficients can be implemented in the limit state function for service life prediction of Fib Bulletin 34. We used this approach to obtain and indication of the expected number of rehabilitation actions within a predefined life span of 100 years, and the extra amount of concrete manufacturing associated with that. The corresponding impact on climate change was calculated with the well-accepted problem oriented impact method IPCC 2007 while considering different allocation approaches (none or by mass/economic value) for the industrial by-product fly ash.