Performance of Na₂SiO₃ solution fly ash based geopolymer mortar under ambient curing

The aim of this study is to investigate the effects of sodium silicate solution with varying concentrations on aluminosilicate- based geopolymer mortars. The total binder content of 600 kg m⁻³ is maintained in all the mix design. The sodium silicate solution with a modular ratio (SiO₂/Na₂O) of 2 had been used. The molarity of the sodium silicate solution varies in the region of 1 < M < 2.5. It can be observed from the test results that there is a significant effect of silicate solution on aluminosilicate based geopolymer under ambient curing. The mix FG2.5 with a high concentration (2.5 M) of Na₂SiO₃ solution had achieved 110 mm mortar flow with sticky mortar because of the high viscosity nature of solution which shows compressive strength of 46 MPa at 28-day. The geopolymer mortar mixes containing 2 M, 1.75 M and 1.5 M showed low viscosity mortar with a slight decrease in strength as compared to 2.5 M. The SEM and EDX analysis revealed that, with a high concentration of the solution, the geopolymer matrix was densely formed. However, the increase in the concentration of the solution resulted in, low micro cracks on the surface of the specimens at a magnification of 2 μm. The Si/Al ratio of all the mixes laid in between 3.37 to 4.1. Therefore, the concentration of the solution in the region 1.25 < M < 2 has shown the better results with consideration of mortar flow, compressive strength, and microstructural observation. (paper)