Study of the rheological and microstructural properties of a geopolymer binder based on fly ash

Abstract

Geopolymers are a potential alternative substitute for Portland cement binders in some applications. However, there are many unexplored research topics to be conducted on this subject. Thus, this study aimed to investigate the rheological and mechanical properties of geopolymer pastes based on Class F fly ash activated by a solution of NaOH and Na₂SiO₃, with activator/precursor ratios of 0.5, 0.6 and 0.7, by mass. Furthermore, microstructural and chemical analyses. Rheological properties were determined from flow tests with shear rates between 0 s^-1 and 100 s^-1 at 25°C. Mechanical analysis was performed from simple compressive strength tests on the hardened pastes. The results of simple compression indicated better strength values for lower activator/precursor ratios. In flow tests, the material behaved as a pseudoplastic fluid, and, with the increase of the activator/precursor ratio, there was a reduction of apparent viscosity values. Therefore, by evaluating the mechanical and rheological results, it was noticed that the paste that presented the best properties was the one with activator/precursor ratio 0.6.