Chloride penetration in reinforced concrete is a significant issue in the construction sector since it triggers corrosion of steel reinforcements, compromising the structural integrity and durability of concrete structures. This corrosion process, which increases significantly in regions with high chloride exposure, such as coastal areas, poses a serious risk to infrastructure safety and durability. Non-destructive testing (NDT) techniques and recent developments in structural health monitoring (SHM) systems play an important role in detecting such deteriorations reaching a critical stage, allowing for timely and cost-effective maintenance interventions. The integration of modern innovative methods such as near/short wave-infrared (NIR/SWIR) hyperspectral imaging into SHM techniques represents a significant advancement in monitoring and assessment of the health of reinforced concrete structures, potentially offering a non-contact solution to chloride inspection problems.
This study investigates the effectiveness of hyperspectral imaging (HSI) for identifying chloride intrusion in plain concrete samples and examines how varying salt concentrations affect spectral data over time under both dry and wet conditions. SWIR hyperspectral imaging in the range of 950 to 2500 nm is used to analyze five concrete samples exposed to chloride concentrations of 0%, 1%, 3.5%, 7%, and 14%. The samples undergo simulated chloride penetration through 48-hour dry-wet cycles, with each cycle comprising 24 hours of dry and 24 hours of wet conditions. Hyperspectral images are collected at the end of each half of the dry-wet cycle, creating a comprehensive spectra database for both dry and wet conditions. The collected spectra and associated time data are then analyzed to identify changes in the spectrum due to salt presence, highlighting distinct spectral shifts. The results revealed that the presence of chloride crystals is indicated by reflectance changes near 1450 nm and 1950 nm. Additionally, the formation of Friedel’s salts was observed after several cycles, occurring earlier at higher chloride concentrations where the exposure to chloride was enough for the chemical reaction to occur. These findings highlight the effectiveness of hyperspectral imaging in detecting chloride intrusion and represent a significant advancement in non-destructive inspection methods, offering new possibilities for monitoring and maintaining the integrity of reinforced concrete structures.
Keywords: Structural Health Monitoring, Reinforced Concrete, Chloride Intrusion, Hyperspectral Imaging, Dry and Wet Concrete.