EFFECTS OF COMPOSITION OF FLY ASH-BASED ALKALI-ACTIVATED MATERIALS ON COMPRESSIVE STRENGTH: A REVIEW

摘要

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 SiO?/Al?O?, Al?O?/Na?O, 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 SiO?/Al?O? and SiO?/Na?O ratios has been established. There is a critical value of the SiO?/Al?O? ratio at about 4.20 to 4.30, in which the increase or decrease of the compressive strengths at a constant SiO?/Al?O? ratio with various Al?O?/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)? 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 Fe?O? in the fly ash and the silica on the compressive strengths of the FAAMs are also generalised.