The design of massive structures, like cast-on-site foundations for wind towers, is not an easy task for design. In fact, this kind of structure is not specifically taken into account by Eurocode 2 standard. The huge concrete volume requires a huge amount of reinforcement, even if only the minimum amount is selected, and it is not clear if the lateral confinement exerted by the truncated cone geometry, mainly loaded along only one radial direction, corresponding to that characterized by the fastest wind direction, really requires the huge transversal reinforcement conventionally introduced in current wind towers. Within the research programme developed in 2019 between Enel Green Power, the Enel Group company dedicated to the development, construction and operation of renewables across the world, and Politecnico di Milano, an experimental investigation, carried out on prototypes characterized by reduced scales (1:15 for the whole structure and 1:4 for the investigation of the only core foundation, where the cylindrical stem is anchored), was conceived to calibrate a reliable modelling with the aim of being extended to full-scale structure, optimizing the required reinforcement. In this perspective, the use of fibre reinforced concrete can significantly improve the construction time by giving a specific toughness to the whole foundation, limiting also the crack opening and the correlated durability problems in the serviceability limit states.