STUDY OF C-A-S-H STRUCTURE USING ²⁹Si MAS-NMR AND ²⁷Al MAS-NMR

Abstract

Studies on physical adsorption to SiOH sites on the surface of C-（A）-S-H, which is considered to be dominant phase in blended-cement system, have been conducted in order to predict the amount of bound chloride ion in the hydrated cement. However, authors best knowledge, there is no proper model that can reproduce the physical adsorption of chloride on C-（A）-S-H with different Ca/（Si＋Al）ratio. The studies on the structure and the change of the SiOH site due to the change in the Ca/（Si＋Al）ratio are still insufficient because of many unknown parts of the structure estimation based on the bonding state of the atoms. On the contrary, C-S-H structure is changed by Ca/Si ratio, pH, curing temperature, and others. For example, for a high Ca/Si ratio, Si atom of the bridging position becomes less and SiOH site decrease. However, in the case of C-A-S-H, some Si atom is exchanged to Al atom and thus SiOH site changes to AlOH site. The effect of Ca/（Si＋Al）ratio on C-A-S-H structure and SiOH（AlOH）site is still not clear and the structure estimation considering the bonding state of atoms is difficult. Therefore, in this study, we synthesized C-A-S-H with different Ca/（Si＋Al）ratio and studied the detailed structure of C-A-S-H by using ²⁹Si MAS-NMR and ²⁷Al MAS-NMR. Two unknown peaks in the ²⁷Al MAS-NMR spectrum were found, and ²⁹Si MAS-NMR spectrum analysis and structure study were conducted based on this.