Synthesis and characterization of hierarchical porous slag-based geopolymers by ice-templating method

The design of porous structures to meet specific applications is a potential direction for geopolymers to achieve high value-added development of applications, and the use of solid waste such as slag as a raw material for geopolymer preparation is also conducive to the realization of green and sustainable development of resources. This paper presents the study on application of the ice-templating method as an innovative approach for the synthesis of porous slag-based geopolymers, water was used as the pore forming agent and utilizing the inherent chemical consolidation properties of geopolymers to achieve self-curing. This process achieved the reinitiation of geopolymerization within freeze-dried samples, avoiding the necessity for high-temperature sintering and the use of organic dispersants and binders. In this study, the optimal parameters for producing porous geopolymers by the ice-templating method were systematically investigated. To achieve customizable pore structures, it was found that the viscosity of the slurry should remain below 4 mPa·s. The duration of the mixing process was established at 5 minutes, accounting for the influence of viscosity and its subsequent effect on the geopolymerization process. In terms of the comprehensive analysis by some characterization methods, the steam curing was selected as the ideal method for reinitiating geopolymerization. In this research, the porous geopolymers exhibited a trimodal distribution of pores spanning 2 nm to 0.5 μm, 0.5 μm to 5 μm and 5 μm to 300 μm, respectively. It wconcluded that slag-based porous geopolymers with highly connected aligned hierarchical pore structures can be tailored by the ice-templating method. •Using the ice-templating method to synthesize porous geopolymers by a green way.•The key parameters for ice-templating are investigated in the geopolymer system.•The porous geopolymers with a hierarchical pore structure.