The Study on the pH Behavior of the HFSC Leached Solution -The Development of Model Considering the Pzzolanic Reaction-

Yoshida, Yasushi*; Mihara, Morihiro  

The development of low alkalinity cement (high fly-ash contained silica-fume cement, HFSC) has been carried out in JNC. Low alkalinity for this cement is acheved by adding pozzolan materials to ordinary portland cement and Ca ion attributed to high alkalinity is consumed by forming CSH gel. This report shows the calculation model to predict the composition for HFSC reacted solution which considers cement mineral dissolution / precipitation as equilibrium reactions and dissolution for pozzolan material as a kinetic reaction. The dissolution kinetic equation for pozzolan material is also derived from leaching experiment. This calculation model is applied to the leaching experiment where powderd HFSC was reacted with distilled water. As a result of comparison between calculation and experimental measurement at the early stage for leaching the tendency for pH, pH decrease from 12.5 to 11.5 drastically, could be interpreted by this calculation model, however, after this drastic pH decreasing pH predicted by calculation model also shows drastic decrease whereas pH for experiment decreased mildly around pH 11.5. It could be thought that this difference between experiment and calculation is caused by inappropriate modelling for CSH gel dissolution / precipitation of C/S value lower than 1.0. For this C/S range thermodynamic data for intermidiate and end member for solid solution for CSH gel and in addition the reaction kinetic for CSH gel should be examined in detail.