Microstructural Study of Hydration of C3S in the Presence of Calcium Nitrate Using Scanning Transmission X-Ray Microscopy (STXM)

Calcium nitrate (CN) is used widely as an effectively inorganic setting accelerator and antifreeze admixture in concrete structures. In this paper, the multiscale investigation of CN on the hydration of C3S was studied by scanning transmission X-ray microscopy (STXM) combined with near-edge X-ray absorption fine structure (NEXAFS), 29Si MAS NMR, calorimetry, scanning electron microscope, and N2 absorption. It was concluded that the calcium silicate hydrate (C-S-H) surrounds the unhydrated C3S at 1-day hydrated C3S in the presence of calcium nitrate, while portlandite is partly in transformation and is formed partly. Based on Ca L3,2-edge NEXAFS spectra for 1-day hydrated C3S particle, calcium nitrate does not change the structure of the asymmetrically 7-fold coordination of calcium in the C-S-H. Calcium nitrate can accelerate the hydration of C3S to some extent and polymerization of the silicate chains within C-S-H considerably at early age, resulting in the increasing specific surface area