Influence of Si/Al molar ratio and ca content on the performance of fly ash-based geopolymer incorporating waste glass and GGBFS

This study delved into the utilization of waste glass powder (WGP) and ground granulated blast-furnace slag (GGBFS) as a binder and waste glass cullet (WGC) fine aggregate in fly ash (FA) based geopolymer concrete. The inherent characteristics of WGP, WGC, FA and GGBFS can be significantly altered by multiple factors such as sources, combustion temperatures, particle size, and impurity level. To offset the inconsistent characteristics of listed waste materials, this study provides a universal index to quantify and evaluate its reactivity to be used as aluminosilicate precursor and aggregate feedstock Ten distinct groups were examined: in five groups WG replaced fly ash at varying percentages (0, 10, 20, 30, 40%), and in five groups WG was used as a sand substitute with different fly ash and slag ratios (20, 40, 60, 80%). Alkali leaching tests were conducted on WGP, WGC, FA and GGBFS to determine the dissolubility and dissolution rate of reactive silica (Si) and calcium (Ca) within 3 h. The dissolubility and dissolution efficiency demonstrated decent correlations with the mechanical and durability properties of the resultant FA-based geopolymer. Leaching tests demonstrate that Ca from WGP, WGC, FA and GGBFS readily leaches out and reacts in both ambient and oven curing, while Si only exhibits activity primarily in high-temperature environments. Overall, the reactivity of Ca from GGBFS and WG improved by up to 50% and 30% in compressive strength and water absorption, respectively. Moreover, based on alkali leaching test, the most effective molar ratios (Si/Al=3.5-4) demonstrated the highest compressive strength (60-70 MPa), and verified intensively using scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS). Lastly, this study revealed that WGC as fine aggregate with the size of 20 mu m also leached out a significant amount of Ca to the geopolymerization process.