Influence of calcium compounds on the mechanical properties of fly ash geopolymer pastes

The influence of calcium compounds (CaO and Ca(OH)2) on the mechanical properties of fly ash based geopolymers has been studied. Calcium compounds were substituted in fly ash at 1, 2 and 3 wt%, respectively. Curing of the geopolymers was performed at ambient temperature (20 °C) and 70 °C. Addition of calcium compounds as a fly ash substitute improved mechanical properties for the ambient temperature cured samples while decreasing properties for the 70 °C cured samples. Seven days compressive strength of the ambient temperature cured samples increased from 11.8 (2.9) to 22.8 (3.8) MPa and 29.2 (1.1) MPa for 3% CaO and 3% Ca(OH)2 additions, respectively.