Mechanical properties of alkali activated flyash/Kaolin based geopolymer concrete

•Geopolymer concretes reduce green house gas emissions.•Geopolymer concretes were made by fly ash, kaolin, alkalies and sodium silicate.•NaOH gave higher compressive strength as compared to KOH.•Combination of 50% FA and 50% Kaolin gave maximum strength.

Five geopolymer concrete mixes were casted using Fly ash, Kaolin, sodium hydroxide, potassium hydroxide, sodium silicate and aggregates. Portland cement concrete (M30) was used as a reference sample. The effect of temperature, sodium and potassium hydroxides and different superplasticizers on the compressive strength was studied. Portland cement concrete with the same mixture proportion was also casted as control. A total of 245 cubes of 100 mm × 100 mm were crushed including the trial experiments. The cubes were cured in oven at different temperatures (40 °C, 60 °C, 80 °C, 100 °C and 120 °C). The results have shown that the compressive strengths increased with increasing temperature, curing time and type of alkali activators. Naphthalene sulfonate based superplasticizer performed better than other superplasticizers. The compressive strength in the presence of 1.0% Naphthalene sulfonate superplasticizer was found 23.3% and 30.9% higher than in the presence of Melamine–formaldehyde and Polycarboxylate ester respectively. Mechanism of strength development has been discussed.