The effect of various Na2SiO3/NaOH ratios on the physical properties and microstructure of artificial aggregates

Artificial aggregate was manufactured by using geopolymerization of fly ash, with alkaline activators using granulation systems. The activators comprised a mixture of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH). The geopolymerization process formed different microstructure and physical properties. This study aimed to determine the effect of alkaline activators ratios on the artificial aggregate properties for use as road and airfield pavement materials. The laboratory trials explored the impact from Na2SiO3 to NaOH ratios, from 1.5 to 3.0, on the properties of the artificial aggregate. Statistical tests demonstrated that there was a significant effect between different ratios of Na2SiO3 to NaOH on artificial aggregate properties. The absorption value of all Na2SiO3 to NaOH ratios (>3%) did not meet the specification requirements. However, the test results for artificial aggregates with alkaline activator ratios less than 3.0, met the requirements for the properties of hardness, strength and durability, therefore the aggregates were deemed suitable for use as road and airfield pavement materials. The scanning electron microscope results indicated similarity of the geopolymerization reaction for all alkali activator ratios. Overall an activator ratio of 2.5 was recommended to provide the best balance in aggregate properties.