2.2.2. Acidic Activators

Although Alkali activators are the most commonly used means of activation in geopolymers, some compositions rely on the use of acidic activators. For instance, MKbased geopolymer has exhibited remarkable compressive strength, up to 93.8 MPa, via the implementation of phosphoric acid as an activator [26,27]. Moreover, research has indicated that acid-based geopolymers possess higher temperature resistance (up to 1450 ◦C) and superior mechanical properties than alkali-based geopolymers [28]. In addition, recent studies suggest that an innovative phosphoric acid-based geopolymer could function as a dependable and robust fire or heat insulator, as it has a conductivity of no more than 10−<sup>7</sup> S/cm at elevated temperatures [29].
