Geopolymer composite foams reinforced with refractory filler: The effect of curing regime on microstructure, porosity and thermomechanical properties

Porous geopolymers with sustainable dimensional stability at high temperatures represent a noteworthy challenge for the development of thermomechanical, reliable and multifunctional composites. This study reports on the porosity formation of refractory-reinforced geopolymer paste via hydrogen peroxide decomposition. Reinforcing the slurry with ceramic chamotte and cordierite increases the apparent viscosity more than eight times in the interval to 100 s-1 retaining a pseudoplastic behavior. Cordierite particles increase the plastic viscosity at 6 Pa s and yield stress above 28 Pa. Surprisingly, the particulate ceramic filler acts as a porosity-modifier thereby reducing the mesoporosity region. Microstructural and porosity behavior was studied via digital microscopy, SEM, MIP and micro -CT. The wrinkled morphology of ceramics significantly affects the macroporosity formation in the region of 100 mu m reaching a total porosity of 60 vol%. The presence of large pores in the macro region and the high distribution of interconnected porosity in ceramics-reinforced composite foams resulted in compressive strengths ranging from 2 to 10 MPa. The effect of curing rate on porosity was most evident in the cordierite reinforcement which led to the occurrence of large interconnected pores. Based on thermomechanical analysis, the ceramic-reinforced foams show high dimensional stability with a reduction in total shrinkage to -0.71 % at 850 degrees C. These results may foster further developments of innovative routes for the synthesis of geopolymer composite foams for widespread technological applications.