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The hydration of tricalcium silicate (C3S) in the preacceleration stages was studied. The C3S particles carry a positive charge during the early stages of hydration. Following a rapid hydrolysis of C3S, calcium ions adsorbed on the Si-rich surface of C,S particles, greatly reducing their further dissolution, thus initiating the induction period. The [Ca"] and [OH-] continue to increase at lower rates and, because Ca(OH), crystal growth is inhibited by silicate ions, become supersaturated with respect to Ca(OH),. When the supersaturation reaches a value of == 1.5 to 2.0 times the saturation concentration, nuclei are formed, and rapid growth of Ca(OH), and C-S-H is initiated. These products act as sinks for the ions in solution, thus enhancing the further dissolution of C3S.