Sodium glass liquid from glass waste as a user-friendly hardener in structural geopolymer systems

Soluble alkali silicates, known as hardeners, play a vital role in the production of geopolymer binders. Currently, different industrial techniques are used to manufacture soluble alkali silicate from different glassy minerals on a large scale, where the major concerns are related to their reactivity as well as their ability to sustain userfriendliness criteria. This paper aims to maximise the use of glass waste (GW) in geopolymer technology through its combined utilisation as a friendly hardener product and a precursor powder in the production of structural geopolymer binders. Sodium glass liquids (SGLs) from GW were developed to encounter SiO2/Na2O molar ratio (MR) of 1.25 as the threshold level of user-friendliness for soluble silica. Various factors involved in the dissolution of silica were investigated using the Taguchi design of experiments and hierarchical analysis of variances (ANOVA). Optimum SGLs were considered to develop geopolymer binders derived from metakaolin (MK) and 0%, 25% and 50% of devitrified glass powder (DGW). Mixture combinations were algorithmically designed based on targeted chemical and physical ratios of SiO2/Al2O3, Na2O/SiO2, liquid/solid and MK/DGW. Mechanical strength and microstructural characteristics were evaluated on the developed geopolymer binders. Acid washing and tridymite formation significantly increases soluble silica content in SGLs. The chemical adjustment of geopolymers allowed the development of high strength binders of user-friendly hardener and 25% and 50% DGW precursor while reducing the commercial sodium silicate by up to 48%. The creation of Q(2) as a new phase of silica species in user-friendly hardener and the formation of more silanol (Si-OH) groups from DGW compared to metakaolin were shown as the outcome of using SGL hardener and DGW precursor in geopolymer binders.

Automated summary

This paper aims to maximize the use of glass waste in geopolymer technology by utilizing it as a friendly hardener product and a precursor powder in the production of structural geopolymer binders. By adjusting the chemical ratios, high strength, user-friendly, and cost-effective geopolymer binders were developed.