Near-infrared spectroscopy investigation on the hydration degree of a cement paste

Near-infrared spectroscopy is a fast and easy-to-perform technique characterized by high sensitivity regarding water containing systems and for this reason it is a suitable tool for investigating structural modifications of hydrating cementing materials, even if the lack of knowledge in this field makes the interpretation of NIR vibrational bands very difficult. In this paper, the NIR spectrum of a hydrated ordinary Portland cement is extensively investigated and an interpretation of the different bands is proposed on the basis of both experimental evidence and reference to literature. The obtained results were applied to the investigation of cement hydration lasting up to 28 days, analyzing the variations detectable in the shape of the spectrum as the reaction went on. The degree of this variation, quantified through area calculations of the main significant bands, revealed a broad agreement with the degree of hydration of the paste measured by thermal methods. The findings of this research supply a solid foundation for future in-field application of NIR spectroscopy, for example, for investigations on cements with different hydration behavior, or to evaluate the effect of additives on cement pastes and, at a further level, for cement quality control.