Reaction Behavior of SiO2 in Ca(OH)2 Solution (Part 2): In the Case of SiO2 Glass and Ca(OH)2 Solution

Reaction behavior of Ca(OH)2-SiO2 system at 75°C was investigated using silica glass plate as an SiO2 sample by SEM observation, XPS analysis and quantitative analysis of Si and Ca of the reaction products. Reaction of silica glass with Ca2+ at 75°C, which leads to the formation of calcium silicate hydrate C-S-H, was found to proceed in three stages; (1) At the first stage the whole glass surface was covered with the layer containing Ca2+ ion. (2) At the second stage crystalline C-S-H was formed by the reaction between Ca2+ and silica glass surface, and glass surface was exposed. (3) At the third stage the reaction with Ca2+ proceeded at the SiO2 surface, and increases the amount of C-S-H. When the reaction product on silica glass surface at the beginning of the reaction was assumed to be amorphous C-S-H, the ratio of Ca/Si in the product was infinity at first, decreased as the crystal growth of C-S-H proceeded, and finally reduced to be constant. The final ratio of Ca/Si depends on the solution pH. In the solution of pH=10.7 the ratio of Ca/Si of crystalline C-S-H became 1.2.