Influence of alkali solutions on properties of pond fly ash-based geopolymer mortar cured under different conditions

Waste management of pond fly ash containing heavy metals beyond optimum limit is essential, otherwise leaching in the soil, water and air will create many hazardous problems. The best way to utilise pond fly ash is to convert it into geopolymer cement. Geopolymers form a class of binders manufactured by activation of solid aluminosilicate source material with a highly alkaline activating solution and aided by thermal curing. In the past few decades, geopolymer binders have emerged as one of the possible alternatives to ordinary Portland cement binders due to their reported high early strength and resistance against acid and sulfate attack apart, from their environmental friendliness. An experimental study was conducted to assess the activating influences of the combination of different alkali hydroxides and silicates (NaOH/Na₂SiO₃, NaOH/Li₂SiO₃, KOH/Na₂SiO₃ and KOH/Li₂SiO₃) on the mechanical properties of mortars. Geopolymer mortars using sand were cured at 80°C for 4, 8 and 12 h and compressive strengths were determined. Curing was also done by heating in a microwave oven for 10, 20, 30, 40, 50 and 60 min and compressive strengths were determined. Results for compressive strengths in the presence of different combinations of alkalis were compared.