Synthesis and characterization of eco-friendly mortars made with RHA-NaOH activated fly ash as binder at room temperature

In this study, an ecofriendly binder was developed by using rice husk ash (RHA) and sodium hydroxide as the activator alongside fly ash (FA) as the aluminosilicate precursor at ambient conditions. The developed binder was used in the production of mortars with varying proportions of sand. A total of three mortar mixtures were developed with sand to binder ratios of 0.55, 0.83 and 1.11. The corresponding behaviour of the mortars and influence of the sand proportions was assessed in terms of the compressive strength, water absorption, density, porosity. Microstructural investigations such as scanning electron microscopy, energy dispersive x-ray spectroscopy, infrared spectrum analysis and mercury intrusion porosimetry were also used to validate the physical properties. The findings from this study demonstrated that RHA can be used successfully as an activator component in the production of mortars. In terms of the sand content, it was found out that increasing the sand to binder ratio has detrimental effects on the performance of the mortars due to the reduction in the binder content primarily. The microstructure analysis of the mortars made with sand to binder ratio of 0.55 showed a compact and strong structure justifying the higher compressive strength achieved. The MIP analysis confirmed that the formation of C-A-S-H gel at the advanced ages allowed the pores refinement with a significant decrease in the fraction of the capillary and macroscopic pores within the geopolymer mortars.