Mechanical property and microstructure development in alkali activated fly ash slag blends due to efflorescence

Srinivasamurthy, Lakshmikanth and Chevali, Venkata S. ORCID: and Zhang, Zuhua and Longhi, Marlon A. and Loh, Thomas W. and Wang, Hao (2022) Mechanical property and microstructure development in alkali activated fly ash slag blends due to efflorescence. Construction and Building Materials, 332:127273. pp. 1-17. ISSN 0950-0618


Efflorescence of alkali activated materials (AAMs) is caused by alkali leaching and precipitation of carbonated salts, which occurs concurrently with leaching and natural carbonation. Efflorescence is specifically driven by precursor and activator variability in AAMs vis-a-vis phase changes, microstructure, and mechanical properties are not well understood. To that end, this study analyses the effects of long-term (90 days) efflorescence on AAMs with eight varied calcium and activator contents and correlated with compressive and splitting tensile strengths. Microstructural features including N-A-S-H/C, N-A-S-H gel change are analysed using Fourier-transform infrared spectroscopy (FTIR), magic-angle spinning nuclear magnetic resonance (MAS-NMR) and thermogravimetric analysis (TGA). AAMs with 9 wt% Na2O and Ca/(Si + Al) ratio of 0.0 to 0.25 exhibit enhanced efflorescence and dealumination of Al[IV] in N-A-S-H/C,N-A-S-H gels, higher mobility of Na+ ions, and natural carbonation. AAMs with 5 wt% Na2O and Ca/(Si + Al) ratio of 0.0 to 0.25 exhibit lower efflorescence and higher stability, in contrast. Under efflorescence, the binder with 5 wt% Na2O and Ca/(Si + Al) ratio of 0.25 exhibited dealumination and carbonation, and the binders with 5 wt% Na2O and Ca/(Si + Al) of 0.0 to 0.10 showed less dealumination and higher concentration of Al[IV] in aluminosilicate gel, indicative of greater phase stability. This study highlights the criticality of calcium and activator doses in controlling the stability of phase composition and mechanical property, which is essential for the industrial application of AAMs.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Files associated with this item cannot be displayed due to copyright restrictions.
Faculty/School / Institute/Centre: Current - Institute for Advanced Engineering and Space Sciences - Centre for Future Materials (1 Jan 2017 -)
Faculty/School / Institute/Centre: Current – Faculty of Health, Engineering and Sciences - School of Engineering (1 Jan 2022 -)
Date Deposited: 03 May 2022 00:08
Last Modified: 03 May 2022 00:08
Uncontrolled Keywords: Alkali activated materials; Efflorescence; Fly Ash; Geopolymers; MAS-NMR; Slag
Fields of Research (2020): 34 CHEMICAL SCIENCES > 3402 Inorganic chemistry > 340204 Inorganic green chemistry
40 ENGINEERING > 4016 Materials engineering > 401699 Materials engineering not elsewhere classified
40 ENGINEERING > 4005 Civil engineering > 400505 Construction materials
Socio-Economic Objectives (2020): 12 CONSTRUCTION > 1203 Construction materials performance and processes > 120301 Cement and concrete materials
24 MANUFACTURING > 2403 Ceramics, glass and industrial mineral products > 240301 Cement products and concrete materials
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