An in situ real-time monitoring of the hydration and dehydration of building gypsum: Conventional and standoff Raman spectroscopy coupled with chemometrics analysis

The application of conventional and standoff Raman spectroscopy has been a widely explored technique for materials characterization. This study uses Raman spectroscopy coupled with chemometrics analysis to monitor gypsum's hydration and dehydration process. The Raman spectra of the specimens are captured periodically, and the intensity ratios of the selected characteristic Raman bands and the intensity ratios of the characteristics bands are used for chemometric analysis. To determine the statistical significance of the variations of the Raman band intensities with the setting time, a statistical analysis of the intensity ratios was conducted using analysis of variances (ANOVA) followed by Games-Howell post-hoc statistics and pairwise comparison of the groups. As the dehydration progresses and the sample dries, the Raman bands of the water molecule gradually diminish, indicating the loss of water molecules from the specimens. The results demonstrate the capability of the Raman spectroscopy, the chemometric techniques used, and the analysis of variances for distinguishing and monitoring gypsum's hydration and dehydration process. The gradual variation in Raman band intensity ratios and the diminishing bands of water molecules corresponds to dehydration, the loss of water, and the phase transformation from a fluid-like gypsum paste to solid phases.