The effects of SiO2/Na2O molar ratio on the characteristics of alkali-activated waste catalyst-metakaolin based geopolymers

Geopolymers, which are a new form of aluminosilicates, are environmentally friendly materials that exhibit high mechanical strength. Waste catalysts that contain a large amount of amorphous SiO2 and Al2O3 are highly soluble in alkaline solutions. This study investigated, the effects of the SiO2/Na2O ratio (S/N) and various levels of waste-catalyst replacement on the properties of waste-catalyst metakaolin-based geopolymers (WCMBGs). The mechanical and microstructural properties of the materials were studied by performing compressive strength testing, porosity analysis, thermogravimetric analysis, Si-29 magic-angle spinning nuclear magnetic resonance (Si-29 MAX NMR) spectroscopy, and scanning electron microscopy. When S/N was 1.93, WCMBGs containing 10% of the waste catalyst exhibited high compressive strength and low porosity. Thermogravimetric analysis indicated that the weight loss of the materials was related to the structural composition. Si-29 MAX NMR results showed that the major structure of the elements Si and Al was Q(4)(3Al). The experimental results indicated that waste catalyst can potentially serve as a partial replacement for metakaolin and exhibits favorable mechanic characteristics. (C) 2015 Elsevier Ltd. All rights reserved.