Temporal effects on the micro- and nano-structural cement-slag pastes subjected to microwave curing over 7 years

This study examines the changes in the micro- and nano-structures of microwave-cured cement and slag pastes over 7 years. The properties of aged samples were compared with those of young pastes made from the same mixtures. Both young and aged samples were analyzed by XRD, DTA-TG, SEM-EDX, and Solid-state MAS NMR of 29Si and 27Al. It is found that, in addition to the usual components (C-S-H, calcium hydroxide, monosulfoaluminate, trisulfoaluminate, and hydrotalcite-like phases (HT)), the aged samples contained calcium magnesium aluminate hydrate and gibbsite (AH3). Over time, some HT or AH3 integrated into the C-S-H nanostructure as additional layers. These findings suggest that microwaves accelerate the general hydration processes in cement due to thermodynamic effects and selectively activate reactions in the aluminate components. This discovery highlights the potential for using microwaves to manipulate cement reactions.