## 3 Dataset  
The CODEBRIM [15] dataset was developed to address the need for a more diverse collection of structural defects that frequently overlap in real-world scenarios. In practical inspections, visual defects such as cracks, corrosion and surface deterioration are influenced by multiple factors, including lighting conditions, varying angles of image capture and diverse surface characteristics. Therefore, applying DL in this domain necessitates sampling from real-world contexts to ensure that models can deliver accurate and reliable performance in complex, real-life conditions. CODEBRIM [15] includes images from 30 different bridges, each exhibiting various levels of deterioration and structural damage. The CODEBRIM dataset includes images collected under diverse environmental and structural conditions, reflected in variations in lighting, surface textures and types of visible defects. This diversity suggests coverage of a broad range of real-world bridge settings, supporting the generalizability of the trained models in different environments. The dataset covers five common types of defects: cracks, spalling, exposed reinforcement bars, efflorescence and corrosion. Cracks are often critical defects in concrete bridges, as they can lead to reduced structural integrity, decreased durability, increased safety risks, higher maintenance costs and functional degradation [40]. Spalling or delamination can cause a reduction in structural strength and increase in maintenance and repair costs. Severe weather conditions such as acid rain, freeze-thaw cycles and temperature changes can erode concrete, exposing the reinforcement bars. Heavy traffic and constant mechanical wear can erode the concrete surface as well. Corrosion, a critical issue in reinforced concrete structures, arises from the electrochemical breakdown of the reinforcement. Efflorescence in concrete bridges is a common phenomenon and can be indicative of underlying moisture issues. Materials used in concrete bridges, such as cement, aggregates and water, can contain soluble salts. These salts become mobile when in contact with water. Bridges in regions with high humidity, heavy rainfall or near bodies of water are more prone to efflorescence. Overlapping of defects: Concrete defects are intimately linked. The expansion of reinforcement corrosion causes tensile stresses in the concrete, which can lead to cracking and spalling. Exposed bars can be a consequence of spalling. [PERSON] et al. [41] found that exposed bars and spalling defects occurred together more than 70% of the time. Figure 7 illustrates some examples of the single and overlapping of defects. The classification task is formulated as a multi-label, where each image can be associated with one or more defect types. The five annotated defect categories in the CODEBRIM dataset are defined as follows:  
* Crack--visible linear fracture or separation in the concrete surface. Although cracks may exhibit various typologies such as hairline, vertical or diagonal cracks, the CODEBRIM dataset annotates all crack types under a single \"crack\" label. Consequently, our classification model is trained to recognize cracks as a general category. * Spalling--surface flaking or detachment of concrete material. * Efflorescence--white crystalline deposits resulting from salt leaching. * Corrosion stain--discoloration due to rust formation, often near steel reinforcements. * Exposed bars--visible steel reinforcement due to severe concrete loss. These classes are not mutually exclusive and may cooccur in the same image. The CODEBRIM dataset supports multi-label annotations, where multiple defects such as cracks, corrosion and exposed bars may cooccur in a single image. While the dataset does not define composite classes explicitly, such overlaps are represented through simultaneous binary labels. Our model uses sigmoid activation to allow the independent prediction of each defect, enabling robust detection even in overlapping scenarios (e.g., a spalled area with exposed reinforcement and corrosion stains).