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

• Interaction between pores and slurry during the chemical foaming process is analyzed. • The macroscopic properties and pore characteristics of GFC are investigated and correlated. • The alkaline activator affects the macroscopic properties of GFC by changing the pore characteristics. • The different pore characteristics are traced back to the different gas generation rates and different rheological properties of the slurry. 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 Na 2 O 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/m 3 , 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 Na 2 O content and lower modulus ratio, resulted in higher porosity, lower compressive strength, and lower thermal conductivity.