THE INFLUENCE OF THE SILICA/SODIUM RATIO ON THE FLY ASH GEOPOLYMER BINDER

This article investigates the properties of a geopolymer, an alternative binding material to the ordinary Portland cement (OPC), and their dependence on different SiO 2 /Na 2 O ratios in the system. To make the geopolymer polish coal burning fly ash consisting mainly of amorphous SiO 2 and Al 2 O 3 , it was activated with a NaOH solution. While many researches have been done on the Si/Al ratio influence, not many studies have examined the activator solution influence on geopolymer properties. Samples were made with 8 different mix compositions with the SiO 2 /Na 2 O ratio varying within 0.8–3.1. The samples were tested for compressive strength after 7, 14 and 28 days of curing. The mineral composition of each set mix was examined with XRD. Samples with the SiO 2 /Na 2 O ratio equal to 2.0 showed the highest compressive strength. The XRD of these samples showed the presence of low-crystallinity hydrosodalite and a small amount of mullite and quartz. The acceptable strength was shown by samples with the SiO 2 /Na 2 O ratio in the range of 1.5–2.5. Samples with the ratio beyond this range failed to produce enough of the necessary binding agents. DOI: http://dx.doi.org/10.5755/j01.ct.68.1.18873