Utilização de silicatos e aluminossilicatos sintetizados via processamento sol-gel para preparação e avaliação de geopolímeros com diferentes composições e concentrações de ativador alcalino

Abstract

Silicas and aluminosilicates with controlled structure and composition can be used to adjust the structural properties of geopolymers. This study aimed to evaluate the effects of two types of silicas and one aluminosilicate Al2O3.2SiO2 synthesized via sol-gel process on the formation and structural properties of geopolymers. First, geopolymers based on metakaolin were prepared with 0%, 1%, 2%, and 10% substitution by the sol-gel materials. Two by-products rich in amorphous silica (rice husk ash and fumed silica) were used for comparison. Additionally, pure Al2O3.2SiO2- based geopolymers were studied with varying levels of alkaline activator, using metakaolin-based samples as a reference. Results showed that sol-gel silica contents above 2% increased particle aggregation and alkaline solution retention in their internal pores, reducing compressive strength and exacerbating efflorescence of geopolymers. The use of 10% sol-gel Al2O3.2SiO2 mitigated this pathology in less porous formulations, suggesting that secondary AlS structures inhibit Na+ cation diffusion in the hardened microstructure. SEM and porosity analyses indicated that Al2O3.2SiO2-derived structures were more porous and lighter than those from metakaolin. Pure Al2O3.2SiO2-based geopolymers exhibited compressive strength below 10 MPa at 3 days but achieved 28-day strength similar to the reference sample in the formulation with higher sodium content. However, pure Al2O3.2SiO2samples showed a high concentration of unreacted particles and efflorescence levels comparable to the reference geopolymers. These results suggest that sol-gel precursors could enhance the structural properties and stability of geopolymers for structural applications. Still, sol-gel materials appear to require higher alkaline activator content for geopolymerization compared to metakaolin, necessitating optimized formulations to balance sol-gel particle consumption with the chemical stability of the resulting geopolymers.