Spectra signature assessment in relation to CDWs quality using hyperspectral imaging in VIS-NIR range

Hyperspectral imaging (HSI) represents an advanced and versatile technique for the analysis and discrimination of materials based on their spectral signatures, allowing the composition and purity state of a sample to be non-destructively characterized. In this work, various materials (both virgin and recycled), also conditioned by contaminants, were evaluated to understand how the presence of sodium chlorides (NaCl), sodium sulfate (Na2SO4), and calcium sulfate (CaSO4) can influence their spectral response and the consequent possibility of distinguishing them from the corresponding ‘pure’ reference samples. The main objective was to establish an HSI-based investigation protocol capable of highlighting even minute variations in the purity of the materials analyzed, contributing to the development of more effective quality control procedures with a view to enhancing the valorization of such materials. During the analysis, hyperspectral images were acquired in a wavelength range from 402 to 998 nm (i.e., VIS-NIR range) suitable for capturing the spectral peculiarities of the materials considered, paying particular attention to the regions where contaminants are more evident. The results showed that using this type of technology it is possible to uniquely identify each contaminant, even in small percentages, and to quantify the impact that the addition of salts such as NaCl,Na2SO4, and CaSO4 exerts on the optical properties of the tested materials. Finally, the potential of HSI offers interesting prospects for the optimization of industrial processes, the verification of quality standards, and the research into innovative materials and circularity in the construction industry.