ORIGINAL ARTICLE Fiber orientation during casting of UHPFRC: electrical resistivity measurements, image analysis and numerical simulations Laetitia Martinie • Jean-Franc ¸ois Lataste • Nicolas Roussel Received: 29 April 2013 / Accepted: 22 October 2013 / Published online: 5 November 2013 Ó RILEM 2013 Abstract Fibers are added to cementitious materials to enhance their mechanical behavior in hardened state. This reinforcement is strongly influenced by the fiber preferred orientation induced by casting flow. In this paper, a model derived from the evolution of a single rigid fiber orientation in a Newtonian medium is proposed to numerically predict fiber orientation in a cementitious structure in hardened state. The main characteristics of fiber orientation during a pouring representative of industrial castings are detailed. Experimental measurements taken on the same refer- ence casting confirm this hardened state orientation. Keywords Fibers  Orientation  Cementitious materials  Predictions  Simulations  Electrical resistivities 1 Introduction Fibers have been added to cementitious materials since their first use in order to enhance the resulting materials mechanical behavior. Indeed, at the mean material level, high concentrations of short fibers lead to higher mechanical strengths of ultra high perfor- mance fiber reinforced cementitious materials (UHPFRC). But, most of the time, at the structural scale [1–3], longer fibers confer ductility to structures in order to provide safety to users [4–14]. Nowadays, UHPFRC combine very high mechan- ical strengths [15–18] and adequate workability [19]. In the fresh state, the cementitious material behavior is however strongly influenced by fiber addition. First, while the material is flowing, mechanical interactions between fibers dissipate energy, which leads to an increase of the yield stress of several orders of magnitude when the fiber interactions network becomes percolated [19]. Then, the orientation of a population of fibers induced by a casting flow can induce anisotropy, which locally modifies the material rheological properties. After setting, the fiber orienta- tion strongly influences the load necessary to pull out a fiber from the matrix [13, 20–24]. The orientation of a population of fibers induced by a cementitious material casting flow has already been derived from the orientation of a single fiber immersed in a Newtonian solvent in simple steady state flows [25]. The orientation process is due to both the finite size of the fiber and the torque exerted by the L. Martinie (&) LaMCoS-UMR 5259, INSA Lyon, 69621 Villeurbanne, France e-mail: laetitia.martinie@insa-lyon.fr J.-F. Lataste I2M-UMR CNRS 5295, Universite ´ Bordeaux 1, 33405 Talence, France e-mail: jean-francois.lataste@u-bordeaux1.fr N. Roussel IFSTTAR, 77447 Marne la Valle ´e, France e-mail: nicolas.roussel@ifsttar.fr Materials and Structures (2015) 48:947–957 DOI 10.1617/s11527-013-0205-3