Corrosion-induced cracking in reinforced concrete: the role of concrete cover thickness

Abstract

The influence of concrete cover thickness on corrosion-induced crack initiation and propagation in reinforced concrete structures is investigated, employing advanced 3D imaging and material analysis techniques. Two cylindrical specimens of small cover (SC) with diameters of 50 mm and large cover (LC) with 75 mm were fabricated. Distinct patterns are observed in crack initiation and propagation dynamics between the SC and LC samples. Specifically, crack initiation in the SC sample occurs independently of void proximity to reinforcement bars, whereas in the LC sample, crack initiation is closely associated with voids and corrosion products, indicating the influence of thicker concrete cover on crack initiation patterns. Raman spectroscopy analysis highlights the prevalence of iron hydroxide compounds in regions of crack initiation and growth in the SC sample, emphasizing the role of pore saturation in crack initiation. X-ray Computed Tomography (CT) imaging provides additional insight into the impact of concrete voids on crack propagation. The sample with a higher concentration of voids (SC) notably aids in the propagation of cracks by facilitating their movement through existing void spaces. Additionally, Scanning Electron Microscopy (SEM), mapping, and Energy Dispersive X-ray Spectrometry analyses reveal substantial differences in corrosion product distribution between the SC and LC samples, with the SC sample demonstrating higher quantity and deeper penetration of corrosion products. The presence of iron hydroxides, particularly lepidocrocite and goethite compounds, in the LC sample’s leak-off zone indicates their significant influence on crack propagation behavior. Understanding the crack initiation and propagation mechanisms provides valuable insights for corrosion mitigation strategies in reinforced concrete structures.