Document Type : Review Article
Authors
1
Assistant Professor, Department of Civil Engineering, Faculty of Mining, Civil, and Chemaical Engineering, Birjand University of Technology, Birjand, South Khorasan, Iran.
2
Associate Professor, Department of Materials Engineering, Faculty of Mechanical and Materials Engineering, Birjand University of Technology, Birjand, South Khorasan, Iran.
10.30501/acp.2026.591221.1202
Abstract
Geopolymer-based ceramics are composed of aluminosilicate raw materials that can undergo polymerization reactions using alkaline activators and transform into ceramics following heat treatment in the 800 to 1200°C range. During this process, the originally formed amorphous structure is subjected to the formation of ceramic crystalline phases, allowing one to reduce the amount of porosity and increase the material density. In terms of its further application, four classes of initial materials were selected: (1) natural aluminosilicates (basalt, volcanic ash, kaolin, metakaolin, illitic clay), (2) industrial wastes (fly ash, blast furnace and steel slags, ceramic waste), (3) additives (waste glass powder, basalt fibers) and (4) alkaline activators (sodium and potassium hydroxides, silicates, sodium aluminate). On the basis of the results of the research, using the associations of oxides it was possible to predict the mechanisms of formation of geopolymer ceramics for each group. It should be noted that this approach was not used previously for this system. In this context, it was found that the predominant mode of ceramicization can be selected on the basis of SiO2 /Al2O3 and (CaO+MgO)/SiO2 ratios. For instance, metakaolin (SiO2 /Al2O3 =1.9) allows one to expect the achievement of compressive strength of up to 95 MPa due to the crystallization of N-A-S-H gel. In turn, blast furnace slag containing about 40% calcium oxide will provide the formation of a liquid phase at 800-950oC due to the C-A-S-H gel. Thus, four main mechanisms of ceramization were found: (1) the formation of N-A-S-H vs. C-A-S-H gels, (2) the viscous flow sintering, (3) the crystallization of ceramic phases (leucite, mullite, cordierite) and (4) the self-healing of the glassy phase, thereby reducing the open porosity to less than 1%.
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