Implicaciones de la alineación predecible de fibras metálicas mediante campos magnéticos en materiales cementosos para el diseño y construcción de estructuras superficiales

• Autores: Víctor Pérez Villar
• Directores de la Tesis: Nelson Flores Medina (dir. tes.), Jesús Anaya Díaz (codir. tes.)
• Lectura: En la Universidad Politécnica de Madrid ( España ) en 2017
• Idioma: español
• Tribunal Calificador de la Tesis: Francisco Hernández Olivares (presid.), Alfonso García García (secret.), Rafael Talero Morales (voc.), Gonzalo Barluenga Badiola (voc.), María del Mar Alonso (voc.)
• Programa de doctorado: Programa de Doctorado en Construcción y Tecnología Arquitectónicas por la Universidad Politécnica de Madrid
• Materias:
  • Física
    • Electromagnetismo
      • Magnetismo
  • Ciencias tecnológicas
    • Tecnología de la construcción
      • Tecnología del hormigón
• Enlaces
  • Tesis en acceso abierto en: Archivo Digital UPM
• Resumen

  • The main aim of this thesis is to show which key factors are affected when steel fibres are aligned using magnetic fields in fresh cementitious composites. Steel fibres are included as a source of discrete reinforcement in concrete structures (Steel Fibre Reinforced Concrete), and their use has been proven to enhance some material properties, such as strength, due to heightened resistance to cracking and crack propagation. In normal cases, fibres are randomly distributed and, in some fractions of volume of fibres, do not contribute to overall resistance.

    Aligning steel fibres allows us to use fewer fibres with the same ratio of safety in architectural structures, while using current volume fractions of oriented fibres allows us to efficiently enhance the strength of the concrete structure as a final result. Steel fibres are impelled to rotate under homogeneous magnetic fields due to the existence of magnetic torques, in order to reach aligning orientations parallel to the magnetic fields. This magnetic torque is always opposed by the viscous properties of fresh cementitious composites. Rheology studies the nature of such viscous properties of flowing fluids. That is why this study also looks more deeply into rheological properties of cementitious pastes or mortars. Some of those rheological properties are focused into the (dynamical/static) yield torque as well as into the viscoplastic one. Defining a new procedure to measure the viscous resistive torques in steel fibres, and their possible causes, such as granulometry of aggregates, the cement/water ratio, the use of additives and type of cement is a key task to determining the fibre behaviour during exposure to the magnetic fields.

    The key idea here is that the magnetic torque of steel fibres immersed in the fresh composites must overcome the viscous torques, and this magnetic torque is a function mainly of magnetic flux intensity B the Helmholtz coil and magnetic dipole moment ~μ due to the ferromagnetic material the fibres are made of steel. The rheological behaviour of cementitious composites seems to follow the Bingham model, which relies on fibre rotation, with a initially high static yield torque at the beginning of movement, a viscoplastic torque proportional to the rotating fibre, and finally the dynamic yield torque present when the fibre stops moving. The study presented here shows how these three rheological parameters affect the cinematic properties and also the final orientation of fibres.

    As a secondary aim within this work, an initial theory about the orientation strategies of steel fibres was developed considering only discrete reinforcement in superficial structures. This theory initially developed, is based on the stress analysis theory, considering the stress trajectories within the surface structures as concrete shells. It is well known that concrete has more resistance to compressive forces than to tension, so the strategy is to orient the fibres to reinforce only the tensile stress trajectories in order to compensate structural weak- ness. The final part of this thesis analyses the enabling technology around this idea in construction areas, such additive manufacturing.

    Taking the idea of discrete reinforcement, in the context of controlled orientation and positioning of fibres using magnetic fields, such reinforcement could be considered in complete symbiosis with the cementitious composites matrix, enabling a reinforced meta-structure inside the superficial member able to create ad hoc a new material, with some controlled enhanced material properties. This new technology of reinforcement could therefore lead to the design of new architectural forms.