Enhancing illitic-clay geopolymer production: A comparative study of conventional method and mechanosynthesized pre-geopolymer powder

Abstract

This study investigates the development of an environmentally sustainable production process for clay-based geopolymers. An illitic clay (IC) sourced from the Fes-Morocco region served as the aluminosilicate precursor after calcination (CIC), which was then activated using an alkaline mix (AM) composed of potassium hydroxide (KOH) and sodium silicate (SS). The pre-geopolymer powders (PGP) were generated by dry-mixing of milled CIC powders with alkaline activators, using various mass ratios of IC/AM and SS/KOH. This mixture underwent milling for brief durations of 3 and 5 min at 400 rpm, employing a planetary ball mill device. The resulting PGP was subsequently hydrated with water to form geopolymer pastes (MGP), which were then cured at 20 °C and 50 % relative humidity. Geopolymer pastes, prepared conventionally using the same mixture design (with a liquid form of sodium silicate) and curing conditions, were also included for comparative analysis of rheological, structural, and mechanical properties with the mechanosynthesized counterparts. The results of the study revealed that the mechanosynthesis process induced significant changes in the properties of the produced geopolymers. X-ray diffraction (XRD) analysis indicated a transformation in mineralogical composition towards amorphization, which is crucial for the formation of the desired Sodium-aluminium-silicate-hydrate(NASH) geopolymer network. Rietveld quantification further confirmed this by highlighting an increase in amorphous content and a decrease in crystalline phase content in the pre-geopolymer samples. Mechanosynthesized geopolymers with higher yield stress and storage modulus showed superior mechanical properties. Moreover, strain sweep analysis revealed greater stiffness and resistance to deformation in mechanosynthesized geopolymers compared to the conventional ones. Finally, compressive strength tests showed that mechanosynthesized geopolymers achieved significantly higher strengths than the conventionally prepared geopolymers, reaching up to 64 MPa after 28 days of curing. This result underscores the efficacy of mechanosynthesis in enhancing geopolymer properties.