Parametric analysis of the production of alternative sodium silicate applied in alkali-activated materials

Abstract

Although alkali-activated materials (AAMs) are considered potential substitutes for Portland cement, they still come with elevated costs and significant carbon dioxide emissions. The development of alternative activators, such as sodium silicate based on the dissolution of rice husk ash (RHA), could partially overcome these disadvantages. However, to maximise the mechanical performance of AAMs, the production of RHA-based sodium silicate (RHA-SS) needs to be fully understood. The production process of an alternative RHA-SS activator was thus investigated through experimental evaluations of RHA grinding time, RHA dissolution time and thermal curing temperature and time. Mechanical performance was evaluated through compressive strength tests carried out on alkali-activated pastes made up of metakaolin, as a precursor, and two different activators (RHA-SS and a commercial sodium silicate). Microstructural features were evaluated through X-ray diffraction, scanning electron microscopy and thermogravimetry analyses. Optimal production was obtained for a grinding time of 30 min, a thermal curing temperature of 40°C, dissolution time of 6 h and a thermal curing time of 8 h. The results show the efficiency of the alternative alkaline activator, which may represent a technically viable solution for larger scale application to AAMs.