Estimating the hydration degree of cement paste using micro X-ray computed tomography (X-ray μCT)

The degree of hydration is a critical parameter for assessing cement hydration progress. In this study, X-ray μCT is employed to characterize the hydration process of cement paste. The morphological evolution of different phases in cement paste - such as anhydrous cement, pores, and hydration products - is visualized and tracked through the acquired CT images. The volume of these phases is quantified, enabling direct estimation of the degree of cement hydration. The hydration degrees obtained from μCT images closely align with those derived from both chemically bound water and Ca(OH)₂ quantification methods, with deviations generally within 10 %, demonstrating the feasibility and accuracy of X-ray μCT. Furthermore, when combined with the Powers-Brownyard model, X-ray μCT analysis can estimate the hydration degree without prior knowledge of the cement type, original cement content, and water-to-cement ratio. The deviation between this CT-model method and direct CT measurement is below 10 % after 28 days. This makes it a valuable tool for evaluating hydration states in existing concrete structures where original mix design information may be unavailable.