The extremely low permeability of Ultra High Performance Fibre Reinforced Concretes (UHPFRC) associated to their outstanding mechanical properties make them especially suitable to locally "harden" reinforced concrete structures in critical zones subjected to an aggressive environment and to significant mechanical stresses. UHPFRC provide a unique and robust solution to simplify the construction process, dramatically reduce the duration of sites, and save money with long term durability. Rehabilitations, especially with cast on site UHPFRC are among the most demanding applications for those materials and require a significant strain hardening response under tension. Achievement of tensile strain hardening, extremely low permeability and self-compacting character is indeed a challenge that few current UHPFRC recipes can satisfy. Cement-superplasticisers compatibility issues severely restrict the range of possibilities to develop new UHPFRC recipes based on locally available components with the required properties for cast in situ applications. An original concept of Ultra High Performance matrix has been developed that makes the application of UHPFRC technology feasible with a wide range of cements and superplasticisers, with outstanding mechanical and protective performance, without significant loss of workability. This concept is an extension to UHPFRC materials of the concepts of cements blended with Limestone fillers, already applied successfully to a wide range of normal or high performance concretes. In a further step, the rheology of those mixes has been adapted to enable them to support challenging 5 % slopes of the substrates at fresh state. The development of this new technology and its portability in various countries opens very promising perspectives for the dissemination of this concept not only for rehabilitation but also for various applications of UHPFRC, prefabricated or cast-in-situ. This document presents both a general methodology for the tailoring of UHPFRC recipes (fibrous mix and matrix) and its application to Slovene and Polish components.