Foaming processes and properties of geopolymer foam concrete: Effect of the activator

In this paper, an ambient-cured geopolymer foam concrete (GFC) was produced based on the chemical foaming method, in which the mixed fly ash (FA) and ground granulated blast furnace slag (GGBS) were used as the precursor, water glass was used as the alkaline activator and aluminum powder was used as the foaming agent. The different properties of the alkali solution, including Na2O contents (i.e., from 4% to 7%) and modulus ratios (i.e., from 1.1 to 1.5), were adopted in the mixture design and the resultant properties were compared for investigating their effects. The density, compressive strength, and thermal conductivity of the GFC ranged within 280.8 ∼ 865.8 kg/m3, 1.10 ∼ 8.13 MPa, and 0.088 ∼ 0.20 W/(m × K), respectively. In addition, more attention was paid to the properties of GFC during the foaming process, including the gas generation rates and rheological properties of the geopolymer slurry, which were determinants of the pore characteristics (e.g., porosity, pore size distribution and roundness) and the macroscopic properties of the GFC (e.g., density, compressive strength, and thermal conductivity). The test results indicated that the higher gas generation rate and lower viscosity of the slurry, which were obtained at higher Na2O content and lower modulus ratio, resulted in higher porosity, lower compressive strength, and lower thermal conductivity.