Effect of solid-to-liquid ratios on the properties of waste catalyst–metakaolin based geopolymers

•WCMBG samples contained 10% waste catalyst exhibited greater compressive strength and lower porosity.•Geopolymer samples were filled the pores, thus leading to the formation of a denser structure.•WCMBG samples showed the major structures of the Si and Al are Q4(3Al) and Q4(2Al).•The porosity of a WCMBG increases with the level of waste catalyst replacement.•We report effect of solid-to-liquid ratios of waste catalyst–metakaolin based geopolymers. In this study, the changes caused by adding a waste catalyst on the properties of the final product were investigated by applying curing on samples of waste catalyst metakaolin-based geopolymers (WCMBGs) prepared with different solid-to-liquid (S/L) ratios (0.66–0.81) and at different waste catalyst replacement levels (0–40wt.%). The mechanical properties of WCMBG samples, such as compressive strength and porosity, were determined after the curing process. Thermogravimetric and differential thermal analysis (TG/DTA), 29Si magic-angle spinning nuclear magnetic resonance (29Si MAS NMR), and scanning electron microscopy (SEM) were also used to determine their microstructural properties. When the S/L ratio was 0.76, WCMBG samples contained 10% waste catalyst exhibited greater compressive strength and lower porosity which were comparable with pure metakaolin samples. The TG/DTA results indicated that WCMBG samples contained 10wt.% waste catalyst had more structural water and geopolymer gels. The results of 29Si NMR spectroscopy of the samples showed that the major structures of the Si and Al are Q4(3Al) and Q4(2Al), and strong resonances were between −85 and −95ppm, respectively. Furthermore, the waste catalyst was the compromising resource material in preparing geopolymers.