Influence of Concrete Cover Thickness on Magnetic Field–Based Nondestructive Monitoring of Reinforced Concrete Structures

Abstract

Abstract Structural health monitoring of reinforced concrete elements increasingly requires nondestructive techniques capable of assessing the internal condition of embedded reinforcement. This study investigates the feasibility of using the passive magnetic response of reinforcing steel as an indicator of strain when subjected to uniaxial tensile loading. The experimental program evaluates three key aspects: (1) the correlation between surface magnetic field intensity and strain, (2) the attenuation of the magnetic signal as a function of concrete cover thickness, and (3) the evolution of the magnetic response during the transition from elastic to plastic behavior of the steel. Tensile tests were conducted on reinforced concrete specimens with cover thicknesses ranging from 20 to 75 mm, while measuring magnetic field and strain simultaneously. The results demonstrated a strong and consistent linear correlation between magnetic field and strain in the elastic range, a predictable attenuation trend governed by magnetostatic dispersion through concrete, and a clear magnetic signature associated with yield and plasticity. Despite signal reduction, the magnetic response remained detectable and informative up to the maximum cover thickness prescribed by structural design codes (75 mm). These findings confirm the potential of passive magnetic monitoring as a noninvasive and effective technique for assessing the mechanical condition of embedded reinforcement in concrete structures.