Abstract: Using calcium hydroxide and sodium silicate as starting materials, two kinds of calcium silicate hydrates, CaO•SiO₂•H₂O and 2CaO•SiO₂•1.17H₂O, were hydro-thermally synthesized at 120℃.The reaction rule of calcium silicate hydrate in aluminate solution was investigated. The result shows that CaO•SiO₂•H₂O is more stable than 2CaO•SiO₂•1.17H₂O in aluminate solution and its stability increases with the increase of reaction temperature but decreases with the increase of caustic concentration. The reaction between calcium silicate hydrate and aluminate solution is mainly through two routes. In the first case, Al replaces partial Si in calcium silicate hydrate, meanwhile 3CaO•Al₂O₃•xSiO₂•(6-2x) H₂O (hydro-garnet) is formed and some SiO₂ enters the solution. In the second case, calcium silicate hydrate can react directly with aluminate solution, forming hydro-garnet and Na₂O•Al₂O₃•2SiO₂•nH₂O (DSP). The desilication reaction of aluminate solution containing silicate could contribute partially to forming DSP.

Key words: calcium silicate hydrate; aluminate; caustic; reaction behavior