Ferromagnetism of concrete

Abstract

Studying the intrinsic properties of concrete is essential for addressing various aspects of concrete structure design, material selection, and sustainability. In this study, a suspended strong magnetic torsion balance device was designed and constructed to investigate the ferromagnetic properties of concrete specimens and their constituent materials. It was found that sand and cement generally exhibit ferromagnetic properties, while aggregates do not possess ferromagnetic properties. Analysis using powder X-ray diffraction (XRD) and chemical experiments confirmed that the ferromagnetic material in sand and cement is elemental iron. A simplified calculation formula for the magnetic force between concrete specimens and an external magnetic field was derived. Three sets of specimens were designed and fabricated for experimental exploration of ferromagnetic properties and magnetic force measurements. The experimental results demonstrate that plain concrete possesses measurable ferromagnetic properties. The magnetic force of concrete initially experiences a rapid decay followed by a gradual leveling off as the distance (from the magnetic field source to the concrete surface) increases. The decay rate approximately follows a fourth-power relationship with distance. Under a loading condition with an applied magnetic field intensity of 0.2 T, the optimal measurement range for ferromagnetic force in concrete is between 0.02 m and 0.05 m.