Effect of nano-silica on strength and durability of fly ash based geopolymer mortar

• Addition of nano SiO2 in geopolymer mortar improves strength and durability.
• Optimum strength at ambient temperature due to addition of 6% of nano SiO2.
• Water absorption and RCPT shows appreciable improvement with addition of nano SiO2.
• Presence of crystalline compound is more in nano SiO2 modified geopolymer mortar.

In general, the fly ash based geopolymer concrete/mortar needs heat activation for early strength developments depending on the molar concentration of activator. To overcome the above shortcomings, an experimental program has been taken up on low calcium fly ash geopolymer mortar having three molar concentrations (8 M, 10 M and 12 M) of activator liquids along with different percentage of nano silica addition (0%, 4%, 6%, 8% and 10% of fly ash). Geopolymer mortar with the addition of 6% nano silica shows appreciable improvement in compressive, flexural and tensile strength at 28 days under ambient temperature curing. The water absorption and charge passed in RCPT are also seemed to be comparatively less for 6% addition of nano silica modified geopolymer mortar. Such improvement of nano silica modified geopolymer mortar is due to transformation of amorphous compound to crystalline compound as noted in the XRD and FESEM analysis.