The binding of chloride ions by pozzolanic product in fly ash cement blends

The hydration and microstructural development of Portland cement and fly ash blends have been examined when chlorides were present in the mix and in the curing solutions. X-ray diffractometry and thermal analysis were used to identify hydration products and determine pozzolanic activity at various stages of reaction. Changes in microstructure were monitored using electron microscopic techniques. The initial rate of hydration and pozzolanic reaction were accelerated when the mixing water contained chlorides. Chlorides were complexed as chloroaluminate or chloroaluminoferrite hydrates, which formed from reacting C₃A, ferrite and calcium aluminate hydrates present in the cement pastes. Additional chlorides may be complexed in fly ash cement blends from calcium aluminate hydrates produced by the pozzolanic reaction.