Effects of Si/Al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature

Good structural performance in a fire scenario necessitates that the structural material possesses chemical stability, deformation resistance and strength endurance. Excellent chemical stability for geopolymers has been reported in literature at a microscale. However, their performance at macroscale...

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Main Authors: Lahoti, Mukund, Wong, Keng Khang, Yang, En-Hua, Tan, Kang Hai
Other Authors: School of Civil and Environmental Engineering
Format: Article
Language:English
Published: 2020
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Online Access:https://hdl.handle.net/10356/142515
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Institution: Nanyang Technological University
Language: English
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spelling sg-ntu-dr.10356-1425152020-06-23T05:10:03Z Effects of Si/Al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature Lahoti, Mukund Wong, Keng Khang Yang, En-Hua Tan, Kang Hai School of Civil and Environmental Engineering Engineering::Civil engineering Geopolymer Metakaolin Good structural performance in a fire scenario necessitates that the structural material possesses chemical stability, deformation resistance and strength endurance. Excellent chemical stability for geopolymers has been reported in literature at a microscale. However, their performance at macroscale has not yet been systematically explored and the underlying mechanisms remain unexplained. In current study, effect of variation in Si/Al molar ratio on the meso- and macro-scale thermal stability of metakaolin geopolymers has been comprehensively investigated to discover the underlying mechanisms governing the performance. Results show that all the geopolymer samples experienced reduction in compressive strengths after exposure to high temperature up to 900 °C. Although, the geopolymer mixes exhibited good chemical stability at microscale, they possessed poor volume stability at mesoscale with very high thermal shrinkage. It was observed that thermal shrinkage induced crack formation dominates the residual strength for geopolymer mixes with Si/Al molar ratio ≤ 1.50, while densification of matrix is the governing factor of the residual strength for geopolymer mixes with Si/Al molar ratio > 1.50. Re-crystallization of nepheline at high temperature adversely affect the strength by inducing expansion and cracking of the geopolymer matrix. Geopolymer sample with Si/Al ratio 1.75 retained highest strength (6 MPa) because viscous sintering of geopolymer mixes with high Si/Al ratio at temperature beyond 600 °C enables localized healing of micro-cracks and densification of matrix which favored compressive strength gain after exposure to 900 °C. At an even higher Si/Al of 2.0, foaming of unreacted silica upon heating can lead to expansion and cracking of the sample which reduce the strength. It was observed that due to high degree of cracking damage and low residual strength retention, it is essential to improve the macro-scale stability of metakaolin geopolymers for structural fire resistance applications. 2020-06-23T05:10:03Z 2020-06-23T05:10:03Z 2018 Journal Article Lahoti, M., Wong, K. K., Yang, E.-H., & Tan, K. H. (2018). Effects of Si/Al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature. Ceramics International, 44(5), 5726-5734. doi:10.1016/j.ceramint.2017.12.226 0272-8842 https://hdl.handle.net/10356/142515 10.1016/j.ceramint.2017.12.226 2-s2.0-85039763426 5 44 5726 5734 en Ceramics International © 2017 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
institution Nanyang Technological University
building NTU Library
country Singapore
collection DR-NTU
language English
topic Engineering::Civil engineering
Geopolymer
Metakaolin
spellingShingle Engineering::Civil engineering
Geopolymer
Metakaolin
Lahoti, Mukund
Wong, Keng Khang
Yang, En-Hua
Tan, Kang Hai
Effects of Si/Al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature
description Good structural performance in a fire scenario necessitates that the structural material possesses chemical stability, deformation resistance and strength endurance. Excellent chemical stability for geopolymers has been reported in literature at a microscale. However, their performance at macroscale has not yet been systematically explored and the underlying mechanisms remain unexplained. In current study, effect of variation in Si/Al molar ratio on the meso- and macro-scale thermal stability of metakaolin geopolymers has been comprehensively investigated to discover the underlying mechanisms governing the performance. Results show that all the geopolymer samples experienced reduction in compressive strengths after exposure to high temperature up to 900 °C. Although, the geopolymer mixes exhibited good chemical stability at microscale, they possessed poor volume stability at mesoscale with very high thermal shrinkage. It was observed that thermal shrinkage induced crack formation dominates the residual strength for geopolymer mixes with Si/Al molar ratio ≤ 1.50, while densification of matrix is the governing factor of the residual strength for geopolymer mixes with Si/Al molar ratio > 1.50. Re-crystallization of nepheline at high temperature adversely affect the strength by inducing expansion and cracking of the geopolymer matrix. Geopolymer sample with Si/Al ratio 1.75 retained highest strength (6 MPa) because viscous sintering of geopolymer mixes with high Si/Al ratio at temperature beyond 600 °C enables localized healing of micro-cracks and densification of matrix which favored compressive strength gain after exposure to 900 °C. At an even higher Si/Al of 2.0, foaming of unreacted silica upon heating can lead to expansion and cracking of the sample which reduce the strength. It was observed that due to high degree of cracking damage and low residual strength retention, it is essential to improve the macro-scale stability of metakaolin geopolymers for structural fire resistance applications.
author2 School of Civil and Environmental Engineering
author_facet School of Civil and Environmental Engineering
Lahoti, Mukund
Wong, Keng Khang
Yang, En-Hua
Tan, Kang Hai
format Article
author Lahoti, Mukund
Wong, Keng Khang
Yang, En-Hua
Tan, Kang Hai
author_sort Lahoti, Mukund
title Effects of Si/Al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature
title_short Effects of Si/Al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature
title_full Effects of Si/Al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature
title_fullStr Effects of Si/Al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature
title_full_unstemmed Effects of Si/Al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature
title_sort effects of si/al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature
publishDate 2020
url https://hdl.handle.net/10356/142515
_version_ 1681057624945065984