Automated concrete exposed reinforcement and corrosion detection and measurement using coloured illumination

Visual identification of reinforced concrete structure defects is vital to ensuring structural longevity and resilience. This paper explores the use of selective reflection imaging for concrete surface corrosion and exposed reinforcement detection and measurement. Selective reflection occurs when certain image colours are reflected more strongly than others by a surface. This effect can enhance colour contrast, making certain objects in a captured image appear darker. By imaging concrete surfaces using a blue lighting source, the contrast of red-coloured corrosion and exposed reinforcement is enhanced, particularly in greyscale images used by many defect detection algorithms. An inspection algorithm is proposed to segment these features using blue light images and Otsu thresholding, enabling accurate measurement of corrosion surface area. On laboratory slab samples, the algorithm obtained Intersection over Union (IoU) scores of over 84 % when compared to human-defined ground truths. Additionally, the algorithm’s corrosion surface area measurements produced a maximum relative error of negative 8 %. These findings demonstrate how colour-controlled illumination can enhance visual inspections, leading to more efficient monitoring and improved durability of reinforced concrete structures.