ISSN 0862-5468 (Print), ISSN 1804-5847 (online) 

Ceramics-Silikáty 65, (1) 9 - 23 (2021)

Tian Qingbo 1, Sun Shuo 1, Sui Yuwu 1, Wang Yue 1, Lv Zhijie 2
1 School of Materials Science and Engineering, Shandong Jianzhu University, Jinan, China
2 School of Mechanical and Electrical Engineering, Shandong Jianzhu University, Jinan, China

Keywords: Fly ash-based alkali-activated materials, Fly ash, Alkali-activator, Compressive strength, Active calcium

A fly ash-based alkali-activated material (FAAM) is an important member of the alkali-activated geopolymeric family. The compressive strength is one of most important mechanical properties for FAAMs in its use as a construction material. The effects of the components of the precursors from fly ash, an alkali-activator, or additives on the compressive strengths of FAAMs have been reviewed. The SiO₂/Al₂O₃, Al₂O₃/Na₂O, and water/solid (W/S) ratios are crucial in developing the compressive strengths of FAAMs. The strength map, as a function of the change in the SiO₂/Al₂O₃ and SiO₂/Na₂O ratios has been established. There is a critical value of the SiO₂/Al₂O₃ ratio at about 4.20 to 4.30, in which the increase or decrease of the compressive strengths at a constant SiO₂/Al₂O₃ ratio with various Al₂O₃/Na2O ratios is found. The active CaO resource, originating from a ground blast-furnace slag (GBFS), ordinary Portland cement (OPC), or chemical agents, such as Ca(OH)₂ or CaO, is of benefit to the improvement in the strength of FAAMs: however, to avoid the dominant formation of C-A-S-H, N-C-A-S-H, and C-S-H gels instead of N-A-S-H and A-S-H gels, an optimal addition of 7.5% to 10% OPC and a 15% to 20% GBFS replacement is recommended by considering the setting time, workability, and strength development. The effects of Fe₂O₃ in the fly ash and the silica on the compressive strengths of the FAAMs are also generalised.

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doi: 10.13168/cs.2020.0037
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