CHARACTERISATION OF COMPOSITIONAL PHASES IN GEOPOLYMERS BY THE RIETVELD METHOD

Activated alkaline materials represent a sustainable alternative to traditional binders due to their lower environmental impact. Within this group, geopolymer stands out as an inorganic aluminosilicate polymer that is mainly formed by a polymerisation reaction between alumina (Al₂O₃) and silica (SiO₂). Its structure is composed of tetrahedra of [AlO₂] and [SiO₂] linked through shared oxygen atoms, resulting in a three-dimensional network known as polysialate chains.

Geopolymerisation is the process by which this material is obtained. It consists of the activation of raw materials – usually industrial waste or natural resources rich in aluminosilicates – by means of highly concentrated alkaline solutions, followed by a curing treatment. Common raw materials include fly ash, slag, clays, kaolin and metakaolin.

To characterise the structure and composition of these materials, the Rietveld method, an advanced analytical technique used to refine crystal structures from powder X-ray diffraction data, was employed. This method allows fitting a theoretical model to the experimental data by means of an iterative least squares process, with the aim of minimising the difference between the observed and the calculated pattern.

In this study, the Rietveld method was applied to perform a quantitative analysis of the crystalline and amorphous phases present in the material, providing key information on its microstructure and degree of reaction.