Strength development properties of geopolymer paste and mortar with respect to amorphous Si/Al ratio of fly ash

Abstract

The strength development properties of geopolymer paste and mortar with 20–40wt% of sand is analyzed with respect to changes in the Si/Al ratio calculated from a combination of the amorphous Si and Al contents in fly ash and an alkaline activator. Experimental results confirm that the compressive strength of the geopolymer paste is greatly affected by the Si/Al ratio. The geopolymer paste also shows high polymerization reactivity at an early age. Although a direct correlation between the polymerization reactivity of the geopolymer paste and the strength development could not be confirmed from the X-ray diffraction results, the difference in the polymerization reactivity resulting from the strength development is confirmed through scanning electron microscopy. The compressive strengths of the geopolymer mortar with 20–40wt% of sand after aging for 28days are 23.7–26.4MPa, which confirms the possibility of using geopolymer mortar as a construction material.