Physical and mechanical properties of lightweight aerated geopolymer

In this study, it is going to investigate properties of lightweight geopolymer specimens aerated by aluminium powder. It has been established well that aluminium powder can be appropriately used for foaming of traditional concrete. Reaction between aluminium powder and alkali activator in geopolymers of this study caused high porous structures based on the weight ratios of constituent materials. Different specimens were made by changing sodium silicate to sodium hydroxide, and alkali activator to fly ash weight ratios. Fly ash was substituted by aluminium powder with 1.5, 3.0 and 5.0 wt.% in different mixtures. Results indicated that substituting of 5.0 wt.% of fly ash by aluminium powder in the specimens with alkali activator to fly ash weight ratio of 0.35 and sodium silicate to sodium hydroxide weight ratio of 2.5 causes the best foamed specimen with the lowest density. Compressive strength of all aerated specimens were in the range of 0.9-4.35 MPa, which is suitable for using as bricks, fire-resistant panels, buried pipeline and so on. Finally, SEM analysis was conducted to evaluate the microstructure of successfully aerated geopolymer. It was seen that in highly aerated specimens, the foaming reaction is too fast that prevents complete alkali activation of geopolymers and many unreacted fly ash particles remains.