Health Inspection of Concrete Pavement and Bridge Members Exposed to Freeze-Thaw Service Environments (SN-7)

Freeze-thaw (F-T) damage is one of the major durability problems of concrete in cold climates. Studies in recent years have focused on the mechanisms and influential factors regarding this deterioration. However, in comparison to other areas of concrete durability, the ability to estimate the health status and predict the service-life of in-service concrete in F-T environments is less developed. This project aims to develop a time-efficient and effective hyperspectral imaging technique for the inspection of concrete pavement and bridge members exposed to F-T environments, which will provide comprehensive information to decision-makers in maintenance/asset management. The outcomes of the first year will serve as the basis in a later phase of research to train classifiers and map F-T deteriorations in concrete pavement and bridge members, as well as to assist in decision-making for maintenance protocols. Approach and Methodology: Hyperspectral camera can obtain an electromagnetic spectrum for each pixel in an image of a surface and processes information from across the spectrum. The spectral signatures, uniquely associated with certain objects, can be used to identify the materials that make up a scanned object as well as their physicochemical status. As examples, the overall level of absorption may be tied to moisture content and microstructural changes, while the characteristic wavelength at absorption peaks can be used as a spectral feature for certain chemicals generated during a specific process (e.g., calcium-leaching of concrete and corrosion of steel). If trained for inspection of concrete surfaces subjected to F-T cycles, this technology will be able to map the ratings (e.g., residual compressive strength) or characteristic values (e.g., type of chemical reaction products). Any mechanical defects, physical characteristics or chemical features of structural degradation will be explicitly shown on the image. Overall Objectives: After the first year of this research project, the spectra library of chemical components of concrete subjected to different types of F-T deteriorations will be established. In addition, two important correlations between DoS and hyperspectral signatures and between mechanical indicators (e.g., compressive strength and relative dynamic modulus of elasticity) and hyperspectral signatures, will be developed. The obtained knowledge will serve as the basis in the second year to train classifiers and map F-T deteriorations in field concrete pavement and bridge members, as well as to assist in decision-making for maintenance protocols. Scope of Work in Year 1: (1) Establishment of a spectra library, (2) Correlation of degree of saturation and spectral signatures, (3) Correlation of mechanical indicators and spectral signatures.