The optimum curing temperature and time were
75 ◦C and 5 days.
The lightweight geopolymer material with mean bulk density of 0.88 g/cm3 and compressive
strength of 15 kg/cm2 was obtained. Incorporation of 40% RHA to increase starting SiO2/Al2O3
and Na2O/Al2O3 ratios to 22.5 and 1.7 and enhanced the compressive strength of geopolymer paste to
24 kg/cm2 withonly amarginal increase of bulk density to 1.01 g/cm3. However,the geopolymermaterials
with high Na2O/Al2O3 (>1.5) were not stable in water submersion.