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 similar to 30 min. After similar to 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. (C) 2009 Elsevier Ltd. All rights reserved.