Mechanochemical and thermal activation of kaolin for manufacturing geopolymer mortars – Comparative study

Abstract The present study compares two different activating methods of kaolin for the purpose of manufacturing a binding material for geopolymer mortar production. Thermal activation is a well-known procedure, but here, the investigation focused on the influence of heat-treatment temperature and time. In this case a new method, called mechanochemical activation, was applied in parallel using various grinding parameters (grinding time, the mass ratio of sample to grinding body, and rotation speed). The structural and morphological changes of thermally and mechanochemically activated kaolinite were followed by X-ray diffraction (XRD), thermal analysis, and Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM), as well as determination of specific surface area and particle size distribution. The effectiveness of thermal and mechanochemical activation was characterised by compressive strength at 28 days and a calculated “degree of amorphisation”. The results demonstrate that mechanochemical activation is an effective method for producing geopolymers, the maximum compressive strength (55.6 MPa) of mechanochemically activated samples surpassed the best thermally activated one (43.0 MPa).