Effect of particle size and curing temperature on mechanical and microstructural properties of waste glass-slag-based and waste glass-fly ash-based geopolymers

This paper aims to investigate the effects of waste glass particle size and curing temperature on the mechanical properties, microstructure and minerology of waste glass-slag-based and waste glass-fly ash-based geopolymers. Specimens synthesized from ground waste bottle glass of three different particle size distributions (D50 = 49.2 μm, 159.1 μm, and 302.1 μm), ground granulated blast furnace slag (GGBS) and Class F fly ash (FFA) were produced by reacting with alkaline activators potassium hydroxide (KOH) and sodium metasilicate nonahydrate (Na2SiO3·9H2O). The geopolymer specimens were cured at four temperatures (20 °C, 50 °C, 80 °C, 100 °C) for the initial 24 h and then at 20 °C. The compressive strength of the cylinders was tested. Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) were utilized to evaluate the microstructural and mineral characterization. Curing at 80 °C, the geopolymer made by GGBS and waste glass of D50 = 49.2 μm achieved a compressive strength of 46.5 MPa on the 28th day. The glass powder with D50 larger than 300 μm showed relatively low chemical reactivity and hardly had any reaction with the alkaline solution. An increase of curing temperature in the initial 24 h generally accelerated the kinetics and reached a higher extent of reaction, especially specimens added waste glass. Increasing curing temperature from 50 °C to 80 °C improved the compressive strength of most of specimens containing waste glass effectively. The geopolymers synthesized from the mixture of glass powder and slag achieved much higher compressive strength compared to the ones made with pure glass or slag. This was, however, not observed in Class F fly ash due to low calcium content of Class F fly ash.