Uniform Composition of Sol-Gel Synthetic Aluminosilicate Precursor as a Key Factor for the Production of Geopolymers

This paper aims to study the fabrication of geopolymers from precursors synthesized by the sol-gel process. Two precursors were produced: the first one from a physical mixture of silica and alumina synthesized separately by the sol-gel technique, and the second one from a one-step co-condensation sol-gel process. The sol-gel products and a commercial metakaolin were activated with sodium hydroxide and sodium silicate to produce the geopolymers. The physically-mixed precursor did not lead to enough hard geopolymers, thus presenting a rubbery behavior. However, the geopolymers derived from the one-step sol-gel aluminosilicate reached adequate strength at 28 days with a lower density than from the commercial metakaolin. This confirms the good alkaline activity of this sol-gel precursor, which could be an alternative source to produce geopolymers or to be used as a reinforcement additive. Such results also underline that a uniform composition of the precursor is a key factor to produce geopolymers with adequate properties.