Effect of SiO2 and Al2O3 on the setting and hardening of high calcium fly ash-based geopolymer systems

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Effect of SiO2 and Al2O3 on the setting and hardening of high calcium fly ash-based geopolymer systems

Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/218429

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Title: Effect of SiO2 and Al2O3 on the setting and hardening of high calcium fly ash-based geopolymer systems
Author(s): Chindaprasirt, Prinya; De Silva, Pre; Sagoe-Crentsil, Kwesi; Hanjitsuwan, Sakonwan
Abstract: This study investigates the effect of silica and alumina contents on setting, phase development, and physical properties of high calcium fly ash (ASTM Class C) geopolymers. The characteristic rapid setting properties and, hence, limited workability range of high calcium fly ash geopolymers has restricted both development and potential application of these binder systems compared to conventional geopolymer binders derived from bituminous coal, i.e., (ASTM Class F) sources or from calcined kaolin feedstocks. For this study, control of setting and hardening properties were investigated by adjusting SiO 2/Al 2O 3 ratio of the starting mix, via series of mixes formulated with varying SiO 2 or Al 2O 3 contents to achieve SiO 2/Al 2O 3 in the range 2.87-4.79. Foremost is the observation that the effect of varying silica and alumina in high calcium fly ash systems on setting and hardening properties is markedly different from that observed for traditional Class F geopolymer systems. Overall, increases in either silica or alumina content appear to shorten the setting time of high calcium-based systems unlike conventional geopolymer systems where increasing Al 2O 3 accelerates setting. The setting process was associated primarily with CSH or CASH formation. Furthermore, there appears to be a prevailing SiO 2/Al 2O 3 ratio that prolongs setting, rather than Ca 2+ ion content itself, while NASH primarily contributes to strength development. SiO 2/Al 2O 3 ratios in the range of 3.20-3.70 resulted in products with highest strengths and longest setting times. These results suggest that initial predominance of Ca 2+ ions and its reactions effectively help maintaining a SiO 2/Al 2O 3 ratio at which amorphous geopolymer phase is stable to influence setting and initial strength development.
Publication type: Journal article
Research centre: Swinburne University of Technology. Faculty of Engineering and Industrial Sciences
Source: Journal of Materials Science, Vol. 47, no. 12 (Jun 2012), pp. 4876-4883
Publication year: 2012
FOR Code(s): 03 Chemical Sciences; 09 Engineering
Keyword(s): Alumina; Calcium oxide; Fly ash; Geopolymer systems; Hardening properties; High calcium fly ash geopolymers; Setting properties; Silica
Publisher: Springer
ISSN: 0022-2461
Publisher URL: http://dx.doi.org/10.1007/s10853-012-6353-y
Additional information: The authors acknowledge support from the Thailand Research Fund (TRF) through the Royal Golden Jubilee Ph.D. Program (Grant No. PHD 0359/2550), the TRF Senior Research Scholar (Grant No. RTA5480004), and the Australian Catholic University.
Peer reviewed