OPTIMIZATION OF PARAMETERS FOR ALKALI-ACTIVATED BINARY MIXTURES OF FLY ASH AND RECYCLED GLASS POWDER: INFLUENCE OF ALKALI DOSAGE, SILICA MODULUS, AND FLY ASH REPLACEMENT LEVEL

Abstract

Alkali-activated materials (AAM) have risen as a sustainable alternative to OPC concrete by utilizing industrial by-products and significantly reducing carbon emissions. While fly ash (FA) and slag are the most commonly used precursors in AAM, their availability is becoming limited in many parts of the world. For instance, in Canada, the supply of FA is decreasing due to the shift away from coal-fired power plants. Therefore, exploring alternative precursors is necessary to expand the boundaries of base materials for geopolymer production. One such alternative is waste glass, which is also a growing environmental problem due to its non-biodegradable nature and increasing disposal concerns. However, when finely ground, waste glass can be used as a reactive aluminosilicate precursor in geopolymer matrices. This study investigates the feasibility of using Recycled Glass (RGP) sourced in the form of Windows glass (WG), Bottle glass (BG) and MRF glass as a partial replacement of FA in geopolymer mortar production. Three critical variables were considered for each glass type: silica modulus (Ms), alkali dosage (Na2O%), and the FA replacement level with RGP. A Taguchi design of experiments was utilized using Minitab software and nine mixes were obtained for each glass type. Compressive strength tests, and the mortar bar tests for alkali-silica reaction (ASR) were conducted. The results were used to generate strength grade contour plots based on Ms, Na₂O%, and replacement ratios. These contours serve as practical tools for mix design of FA/RGP mortars. Furthermore, predictive models were developed in Minitab for both WG and BG, enabling accurate estimation of compressive strength based on the above-mentioned parameters. Results revealed that replacing FA with RGP up to 50% at Ms value between 1-1.1 and Na2O% in the range of 8-10% exhibited better compressive strength at lower risk of ASR expansion above ASTM limit.