EFFECT OF Al ON THE STRUCTURE AND CYCLE OF C-S-H IN RECYCLABLE CEMENT

Abstract

This paper investigates the Al substitution properties in C-S-H with a Ca/Si ratio of 2.0 obtained by hydrating highly reactive belite, and the regeneration of belite by re-calcinating. The results show that Al was incorporated bridging site in C-S-H with a Ca/Si ratio of 2.0 as 4- and 6-coordinated Al and that the basal spacing increased with an increase in the amount of substitution. On the other hand, belite was regenerated from C-A-S-H with a high Ca/Si ratio by calcinating at 800℃. The crystallite diameter and specific surface area of the regenerated belite were similar to those of the pre-hydrated belite, indicating that the formation of α’-C₂S was predominant over β-C₂S with increasing Al substitution. These results indicate that recyclable cement may sustain the regeneration cycle even if its key element, C-S-H with a Ca/Si ratio of 2.0, is altered by Al.