Early hydration and setting of Portland cement monitored by IR, SEM and Vicat techniques

Diffuse Reflectance Infrared DR-FTIR spectroscopy is employed to monitor chemical transformations in pastes of Portland limestone cement. To obtain a sufficient time resolution a freeze-dry procedure is used to instantaneously ceasing the hydration process. Rapid re-crystallization of sulphates is observed during the first 15 s, and appears to be complete after ~ 30 min. After ~ 60 min, spectroscopic signatures of polymerizing silica start to emerge. A hump at 970-1100 cm^− 1 in conjunction with increasing intensity in the water bending mode region at 1500-1700 cm^− 1 is indicative of the formation of Calcium Silicate Hydrate, C-S-H. Simultaneously with the development of the C-S-H signatures, a dip feature develops at 800-970 cm^− 1, reflecting the dissolution of Alite, C₃S. Setting times, 180 (initial) and 240 (final) minutes, are determined by the Vicat technique. Combining DR-FTIR, SEM and Vicat measurements it is concluded that the setting is caused by inter-particle coalescence of C-S-H.