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

• Published in: Case Studies in Construction Materials Vol. 21; p. e03611
• Main Authors: Li, Dong, Shi, Zhenwu, Pan, Yunshi, Gao, Xiaojian, Li, Shuangxin
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2024; Elsevier
• Subjects: Aged pastes; Hydration; Microstructure; Microwave curing; Nanostructure; Microwave curing; Nanostructure; Hydration; Microstructure; Aged pastes
• ISSN: 2214-5095; 2214-5095
• DOI: 10.1016/j.cscm.2024.e03611

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. •Microwave irradiation effectively accelerates slag hydration for a long term.•Calcium magnesium aluminium hydrate and gibbsite form in the aged pastes.•Aged C-S-H consists of interstratified layers of Al-substituted T-based structure.•HT or AH3 intermixes in the nanostructure of C-S-H as additional layers.