Materials and microstructural characterization of porous geopolymer having fireclay and cordierite

The current fly ash-slag porous geopolymer formulations have low fly ash concentrations and limited porosity. Developing geopolymer porous materials with enhanced porosity is a key priority in advancing this field. One of the major challenges in producing thermomechanically stable, multifunctional composites is creating porous geopolymers (GC) that retain dimensional stability at elevated temperatures. This study examines the role of hydrogen peroxide decomposition in generating porosity in GC paste containing ceramic fillers such as cordierite and fireclay. To assess microstructural and porosity characteristics, digital microscopy, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) were employed. For GC reinforced with fireclay and cordierite fillers, the viscosity values at a shear rate of 100 s^-1 were 4.998 Pa.s and 4.227 Pa.s, respectively. The addition of these ceramic fillers resulted in an eightfold increase in apparent viscosity at 100 s^-1 without compromising the material's pseudoplastic behavior. The yield stress exceeded 24.978 Pa, while cordierite fillers raised the plastic viscosity to over 5.895 Pa.s. The compressive strengths of the composite porous geopolymer mortars containing ceramic fillers ranged from 1.51 to 10.1 MPa, attributed to the high degree of interconnected porosity and large pore size within the matrix. In samples reinforced with cordierite, the formation of large, interconnected pores was strongly influenced by the curing rate. Thermomechanical analysis revealed that the porous geopolymer mortar reinforced with ceramic fillers exhibited excellent dimensional stability and minimal shrinkage (-1.5%) at 850°C. These findings suggest new pathways for developing GC composite porous mortars for diverse technological applications.