Raman Spectroscopy Study on the Hydration Behaviors of Portland Cement Pastes during Setting

In the research reported in this paper, an in-situ observation on the hydration of cement pastes with various water-to-cement (w/c) ratios was implemented by Raman spectroscopy (RS). The RS was applied to study the paste continuously after cement mixing with water until the final setting was complete. Hydration products, including calcium hydroxide (CH), calcium-silicate-hydrate (C-S-H) gel, and ettringite were detected. The CH and C-S-H gel were present consistently with slight intensity changes in the RS patterns after their first detections. In all the pastes studied, the intensity of ettringite remained constant first, followed by a rapid increasing period; thereafter it began to decrease. Within the measuring duration a new peak assigned to monosulfate was detected in the pastes with w/c ratios of 0.35 and 0.40. These Raman detections were also analyzed together with the setting time and heat evolution to elucidate the early hydration mechanism.