2.2.1. Alkali Activators

Numerous studies have demonstrated that the activation of geopolymer materials is achieved through the use of alkali activators. Alkalinity, resistance to chemical attacks, strength development, and durability are all dependent on the type of Alkali activator used. Additionally, the selection of suitable activator solutions is based on the chemical composition and the source of raw materials. Typically, the activation of alkali materials involves the use of sodium- or potassium-based activators (e.g., hydroxides, such as NaOH and KOH), sodium- and potassium-based silicate solutions, and carbonates. Each of these activators has distinct advantages, with sodium- and potassium-based activators being the most commonly used due to their cost-effectiveness and widespread availability. Prior investigations have revealed that, in the case of FA, sodium-based activators exhibit greater activation efficiency than their potassium-based counterparts [24], despite the higher alkalinity in potassium-based solutions [25]. To produce a metakaolin-based geopolymer, sodium waterglass has been used as an activator; the research has shown a compressive strength reaching 63.8 MPa [26].

In addition to conventional activators, ash generated from the incineration of solid waste and organic material can be employed as activators. Moreover, ash sourced from olive oil biomass can serve as an alkali activator for GBFS-based geopolymer production. [16].
