Alkali-activated slag supplemented with waste glass powder: Laboratory characterization, thermodynamic modelling and sustainability analysis

Finding new aluminosilicate wastes to make sustainable alkali-activated materials (AAMs) has gained increasing attention in cement industry. In this work, the ground granulated blast-furnace slag (SG) was incorporated by waste glass powder (GP) as the raw materials for the production of AAMs. Laboratory tests were conducted to analyze the compressive strength and phase assemblages of hardened pastes at increasing ages. Analytical modelling based on Gibbs free energy minimization method (GEM) was implemented to compare with the experimental results and assist in the analysis of relationship between phase assemblage and compressive strength. The results show that GP had a lower reaction rate compared with SG, and about 28 days of curing was required to show its delayed contribution on the mechanical properties. The incorporation of up to 50% of GP into SG did not cause the significant detrimental effect on the late-age strength of AAMs, and the final strength ranged between 33.5 and 33.1 MPa. X-ray diffraction (XRD), thermogravimetric analysis (TG) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-DES) showed the presence of calcium (sodium) aluminosilicate (C-(N-)A-S-H) gels and hydrotalcite phases in the reaction products. In addition, it was found that a higher amount of C-(N-)A-S-H and lower porosity in AAMs generally contributed to a higher compressive strength. The sustainability and cost analysis also confirmed the environmental friendliness and the economic feasibility of incorporating GP in the traditional alkali-activated slag cement, paving the path for the value-added utilization of waste glass in cement industry.