Abstract
The role of individual reactive components and process variables such as molarity and temperature on alkaline activation of different low- calcium fly ash is explored. The oxide ratios in the activated system, based on the total silica (total SiO 2 ) in the system consisting of the reactive silica contributed by fly ash and the reactive alumina in fly ash are shown to provide consistent results for achieving the highest strength. For a given total SiO 2 content in the system, an increase in the sodium content above a certain dosage does not influence the ultimate compressive strength. An optimum (total SiO 2 ) to Na 2 O ratio, equal to 2.66 is established for achieving maximum strength. The role of temperature within the range of 60 o C-85 o C is not significant when the molarity of NaOH is high. A N-A-S- H type gel with Si/Al ratio ranging between 2.5 to 3.0 and the Al/Na ratio varying between 1.30 to 0.9 is formed on decreasing the (total SiO 2 )/Na 2 O ratio from 6.55 to 2.66
Highlights
Alkali activated binders can be made from aluminosilicate source materials
Both the fly ashes exhibit similar tends in compressive strength at any particular age since the total/Na2O ratio is kept same for both the fly ashes, while there is a difference in the working solution ratios
For/Na2O ratio equal to 2.66, maximum compressive strength was achieved at 3 days after which there is very little improvement in compressive strength
Summary
Alkali activated binders can be made from aluminosilicate source materials. The most attractive aluminosilicate source material is fly ash due to its ready availability in a large quantity. The influence of the process variables, such as the temperature of curing and the oxide ratios of the activating solutions on the strength of activated fly ash have been evaluated. Most studies have focused on the influence of molarity of NaOH and the molar ratios of SiO2/Al2O3 and Na2O/Al2O3 in the activating solution on the final strength of activated fly ash [1,2,3,4]. Fly ashes with high reactive content would contribute higher quantities of Si and Al to the final product and may require a smaller addition of Na2SiO3. The influence of sodium content, total reactive oxide ratios, temperature and NaOH molarity on strength development in the alkali activated fly ash is investigated. The influence of sodium content relative to the total reactive alumina contributed by fly ash and the total silica content of the activated system is evaluated
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