Glass and Construction Wastes in Sustainable Geopolymer Systems

Abstract

<p>This research encompassed comprehensive analytical and experimental investigations with the main aim of developing sustainable ambient-cured structural geopolymer binders incorporating maximum amounts of glass and construction and demolition wastes as precursors and hardeners. The objective was also to design a numerical method of mixture for quantifying glass waste (GW) and construction and demolition waste (CDW) ingredients, with different chemical and physical properties, in a balanced geopolymer matrix with optimized rheological, mechanical and microstructural performances. The first challenge was to enhance the reactivity of GW in order to increase its contribution in the geopolymer system, which was reached through a devitrification process to form the tridymite-phase of silica in GW. Furthermore, an alkali hardener was produced from dissolved GW and used to reduce the required commercial sodium silicate while meeting the user-friendliness criteria of alkaline solutions. The enhanced GW was incorporated with metakaolin (MK) as an additional source of alumina and the effect of different amounts of this product was studied at fresh and hardened states. The GW-based hardener was utilized with the enhanced GW and MK precursors, after ensuring optimum factors were attained for dissolved silica using the Taguchi design of experiments and hierarchical analysis of variances. Then, ceramic waste (CW) and brick waste (BW), as the main CDW materials, were combined with the resulting GW and MK combinations in CW-GW+MK and BW-GW+MK precursors prepared with GW-based hardener. The solubility of silica species in alkaline media and the microstructural changes of the enhanced glass waste, as well as the rheological, mechanical and microstructural properties of produced geopolymer binders were investigated using spectrophotometry analysis, X-Ray fluorescence, X-ray diffraction, viscometry analysis, compressive strength measurement, Scanning Electron Microscopy, Energy-dispersive X-ray Spectroscopy and Fourier-Transform Infrared Spectroscopy, respectively. Throughtheresults ofthis research,it was possibleto develop a numerical mix design approach and to generate tridymite as an active silica form of GW. This enabled control of the important chemical and physical factors involved in the geopolymerization process and reach stable, user-friendly and enhanced strength binders with major amounts of GW, BW and CW and up to a 76% reduction in commercial sodium silicate content at ambient curing.</p>