Irreversible, in situ, self-healing and self-glazing of geopolymers

Abstract

Geopolymers are the result of the reaction of alkaline activators with reactive aluminosilicates. By dissolving these aluminosilicates and undergoing processes of polycondensation and geopolymerization, they form robust structures with distinct properties compared to other ceramics. These non-crystalline materials exhibit notable resistance to corrosion, heat, and environmental conditions, such as changes in pressure and temperature. Consequently, geopolymers, e.g., of stoichiometric composition (M2O•Al2O3•4SiO2•11H2O (or 13H2O)), find a place between cement and ceramics regarding mechanical properties. Considering the formulation of geopolymer blends, this study demonstrates that these materials have self-healing and self-glazing properties under high-temperature conditions. Through systematic experimentation and considering the specific properties of sodium-based (Na-GP) and potassium-based (K-GP) geopolymers, a combination of sodium and potassium waterglass compounds with different weight percentages were used to achieve geopolymer materials with optimum self-healing and self-glazing properties. Moreover, these samples were subjected to heat treatment under various time and temperature conditions to optimize their properties in terms of crystallization, and the best results were reported from among these variables. Based on the findings, the specific combination consisting of 75 wt% sodium waterglass and 25 wt% potassium waterglass were the best mixtures. This mixture was heated at a rate of 5 °C per minute to a temperature of 1000 °C and held isothermally for 6 h before being cooled at the same rate. As a result, an amorphous geopolymer turned into a ceramic with irreversible, self-healing, and self-glazing capabilities.