A model about dynamic parameters through magnetic fields during the alignment of steel fibres reinforcing cementitious composites

Abstract

The aim of this paper is to perform a model to understand and to predict the dynamic behaviour of steel fibres immersed in fresh cementitious materials when exposed to Homogeneous Magnetic fields. Fibres behaviour is of especial interest to improve and develop a method to achieve the alignment of fibres in reinforced composites by means of magnetic fields. The torques and forces that a magnetic field summit a ferromagnetic fibre during its alignment find an opposition, in a fresh cementitious composite considered as a Bingham fluid: shear rate (gamma) over dot and yield stress (tau(0)) and plastic viscosity (eta). The torque necessary to rotate a single fibre is determined through a rotational rheometer and the relation between its geometry and the fresh cement rheology is determined. In this work, the alignment of fibres under magnetic fields within the range of 20 mT to 80 mT immersed in fresh mortars and fresh cements is studied. The orientation factor of the fibres after the magnetic field has been obtained. The probabilities of success depending on the initial angle of the fibres are also showed. The model to predict the alignment of fibres in cement-based materials presented here can be used also for different magnetic and rheological ranges.