The strength of concrete is linked to the amount of cement used. In many applications, concrete has a considerably higher strength than designed and structurally required. Lowering cement contents, thus reducing strength, significantly reduces the ecological impact of any concrete in terms of raw materials use and CO 2 output. A lower cement content may be achieved by replacing cement using high amounts of filler (e.g., fly ash) and simultaneously lowering the total amount of cement + filler (powder). The question arises how the required durability of such High Filler (HiFi) concrete for a specific application should be achieved. In the current paper HiFi concrete is tested for chloride penetration, using rapid chloride migration and diffusion tests. Also the microstructure is investigated using polarization-and-fluorescence microscopy on both laboratory samples and samples from pilot projects. The results show possibilities and limitations of HiFi concrete for making a design for long service life.