The correlation between Al incorporation and alkali fixation by calcium aluminosilicate hydrate: Observations from hydrated C3S blended with and without metakaolin
Shihua Wei, Keren Zheng, Wei Chen, Lou Chen, Jin Zhou, Tangwei Mi
Abstract
This study aims to investigate the correlation between Al incorporation and Na fixation by C-(A)-S-H, which was derived from hydrated C 3 S blended with and without 10 wt% metakaolin at 1, 2, and 3 wt% Na 2 O content. C-(A)-S-H compositions were calculated based on mass balance method. NMR was used to calculate the fraction of different coordinations of Si and Al in C-(A)-S-H. Results show that the incorporation of Al into C-S-H enhances the polymerization of silicate chains , it also increases the Ca/Si of the formed C-A-S-H because more Ca ions are required to stabilize the incorporated Al(VI). The increased Ca/Si subsequently decreases the alkali fixation capacity of C-A-S-H compared to that of C-S-H. Increasing alkali concentration favors the polymerization of C-A-S-H by incorporating more Al(IV) in bridging sites and shows less effect on Al(VI)/Si and Ca/Si due to the different negative charges and calcium coordination environment regarding Al(VI) and Al(IV).