Rheological characterization of high performance fiber reinforced cementitious composites

Advanced cement based materials with adapted rheology have been increasingly used in a wide variety of civil engineering applications. Assessing the fundamental rheological properties of fresh cementitious suspensions, generally regarded as Bingham fluids, is essential, not only to formulate optimum mix-designs and to assess the fresh state performance of the mixture, but also to design the casting procedures, the successful accomplishment of which may be discriminated by the rheology of the fluid. Moreover, in the case of fiber reinforced composites, a suitably adapted rheology is necessary in order to achieve a randomly uniform dispersion of fibers within the casting and, together with an ad-hoc designed casting process, to govern their orientation within the formwork, e.g. along the direction of principal tensile stresses within the structural element when in service. Whereas the mechanisms influencing the rheological behavior of cement pastes and mortars are being understood fairly well today, the knowledge about the interaction between such mortars and fibers with different properties and dosages is purely empirical. One of the key aims of this paper therefore is to develop suitable measuring techniques quantifying the rheology of the composite as a function of the rheology of the mineral matrix and of the fiber properties. A commercial rheometer with the so-called Building-Matierials-Cell (BMC)” for cementitious suspensions has been employed in order to identify fundamental rheological properties of high performance fiber reinforced cementitious composites with different amounts and different types of metallic fibers. The role of parameters such as the fiber factor or the excess of paste/mortar thickness will be investigated in order to provide a tool to effectively govern and the rheology of HPFRCCs and adapt it as required by the specific application. This is furthermore meant as instrumental to the design of a casting procedure tailored to the intended application which can discriminate its successful accomplishment and even affect the structural performance.