Effects of Activator Types on Degradation Mechanisms of Metakaolin Geopolymer Mortars Exposed to High Temperature
Publication: Journal of Materials in Civil Engineering
Volume 32, Issue 12
Abstract
In this study, we investigated the degradation process of metakaolin-based geopolymers exposed to high temperatures up to 1,000°C. The changes in mechanical properties, microstructure, and phase assemblage of the samples were studied, and the results demonstrated that at high temperatures the activator type [i.e., (Na/Na) and (Na/K) solution] affected the degradation mechanisms of geopolymer mortars. (Na,K)-based geopolymer specimens demonstrated better thermal resistance at temperatures above 200°C. This was evident from the higher compressive strength, lower porosity, and less cracking tendency of this mixture. Compared to (Na,K)-based geopolymers, more mass loss may result in considerable drying shrinkage of (Na,Na)-based counterparts, which would further lead to the occurrence and development of cracks at . Above 200°C, the degradation of the mechanical properties of geopolymers could be attributed to crack development and degradation of material properties. Furthermore, compared to their (Na-Na)-based counterparts, (Na-K)-based geopolymers achieved improved chemical stability and did not form new crystalline phases above 1,000°C. Moreover, higher temperature exposure (1,000°C) led to significant sintering of geopolymers, forming a dense and homogeneous matrix and, as a result, improved mechanical properties of specimens. Overall, it showed that when specimens were exposed to different high temperatures, the mutual promoted effects between and in geopolymers played a significant role in crack development, sintering, and new crystallization formation in the specimens.
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Data Availability Statement
All data, models, and code generated or used during the study appear in the published article.
Acknowledgments
The authors would like to thank Xiuyu Zhu, Jiahua Deng, Xiaohua Ji, and Yu Peng for their assistance with the experiment. In addition, the authors appreciate the financial support from the National Science Foundation of China (Grant Nos. 51778570 and 51879230).
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Published In
Journal of Materials in Civil Engineering
Volume 32 • Issue 12 • December 2020
Copyright
© 2020 American Society of Civil Engineers.
History
Received: Jun 24, 2019
Accepted: May 29, 2020
Published online: Sep 22, 2020
Published in print: Dec 1, 2020
Discussion open until: Feb 22, 2021
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