Characteristics of metakaolin-based geopolymer mortars activated by a novel alternative activator

The relatively high cost of geopolymers remains a key limitation to their broader implementation. To minimize the dependence on expensive commercial activators such as sodium or potassium silicate, the use of alternative and sustainable activators derived from industrial by-products has become increasingly important. In this context, partially dealuminated kaolin (DK), a residue from the aluminum sulfate industry, was utilized as a source of amorphous silica to partially replace cementitious materials. In the current research, DK was employed to synthesize sodium silicate solution as a substitute for the commercial product in the formulation of metakaolin-based geopolymer mortars. Several preliminary trials were conducted to identify the optimal proportion of DK to sodium hydroxide solution (12M). A detailed experimental program was then designed to evaluate the influence of different parameters on both the fresh and hardened properties of GDMK-M. Four mixes were prepared and cured at ambient temperature to examine the impact of three variables: the DK-to-NaOH ratio, the activator-to-MK ratio, and the water-to-solid ratio. The experimental findings were further validated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The outcomes demonstrated that the DK-NaOH combination can be considered a promising and sustainable alkaline activator capable of enhancing GDMK-M through the geopolymerization process.