REACTION BEHAVIOR OF SIO2 IN CA(OH)2 SOLUTION .1.

Reaction behavior of a Ca (OH) 2-SiO2 system at 75-degrees-C was investigated by the potentiometric titration method. The results of changes in solution pH after reaction and Ca2+ ion concentration indicated that the reaction behavior in this system was classified into three regions. Reaction products obtained in the three regions were identified using X-ray diffraction and observed with a scanning electron microscope. In region I, no changes in solution pH and Ca2+ ion concentration before and after reaction were observed without the appearance of any crystalline phase. Hence, the reaction between Ca2+ ion and SiO2 powder does not occur in this region. In region II, although the C-S-H were not observed by XRD, the amount of reacted Ca2+ ion with SiO2 powder gradually increased with an increase in Ca(OH)2 concentration in initial solution. This result shows that the reaction between Ca2+ ion and SiO2 powder occurred. In region III, changes in the amount of consumed Ca2+ ion before and after reaction increased linearly with an increase in Ca(OH)2 concentration in initial solution. In this region, C-S-H was confirmed and pH values were constant after reaction, which appeared as a pH plateau on the titration curve, regardless of the initial solution pH.