1 MIX DESIGN AND MECHANICAL PROPERTIES OF ULTRA HIGH PERFORMANCE FIBRE REINFORCED CEMENTITIOUS COMPOSITES (UHPFRCC) Demetris Nicolaides † , Antonios Kanellopoulos † , Pericles Savva † , Anna Mina ‡ and Michael F. Petrou ‡ † Frederick Research Center – 7 Filokyprou Street – Pallouriotisa – 1036 – Nicosia – Cyprus. ‡ University of Cyprus – Department of Civil & Environmental Engineering – PO Box 20537 – 1678 – Nicosia – Cyprus. Abstract The research work focused on the determination of guidelines for the production of an UHPFRCC, and the experimental investigation of the mechanical properties of the produced material. The aim of the specific study is to present the results of an extended work on the development of an UHPFRCC with the use of materials available in Cyprus. The fundamental idea for the development of this high performance material is the enhancement of the microstructure of the final product. The incorporation in the mix of extremely fine, pozzolanic particles results in the improved packing within the microstructure, whereas the usage of superplasticizer improves significantly the rheological characteristics of the fresh material. Moreover, the inclusion of small steel fibres in the mix improves substantially the tensile strength of the produced cementitious composite. The study will present results on a broad variety of mechanical properties and the effect of several parameters on the strength and the rheological characteristics of the produced material Keywords: UHPFRCC, microstructure, steel fibres, superplasticisers, properties 1 Introduction There is no doubt that cement and therefore concrete influenced the construction methods and practices in the 20 th century. Concrete, due to its advantage to be placed in formworks of particular sizes and shapes at the fresh state, offers the possibility to the engineer to design structures of a great geometric variation. The construction of tall buildings and impressive structures became feasible due to the combination of the high compressive strength of concrete and the enormous tensile strength of steel. The demand for improved properties of the construction materials increase with time and the related design and construction codes are adapted in an analogous manner. Nowadays, the research on concrete technology has been focused not only in the development of materials with extremely high properties, but also in the development of materials that in addition to their improved mechanical properties they will also have improved durability.