Effect of acid attack on microstructure and composition of metakaolin-based geopolymers: The role of alkaline activator

The mineral composition of raw materials and the type of alkali cation plays an important role in the acidic resistance of geopolymers. This paper focuses on the study of chemical durability in hydrochloric acid of potassium and sodium based geopolymers. The study was carried out on two Algerian kaolins and compared with a kaolin from Charente (France). The acid degradation was studied using X-ray Diffraction, Fourier-Transform Infrared and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy. The samples based on Algerian kaolins seems to have the lowest loss in mass for formulations based on potassium due to the presence of secondary minerals (quartz and muscovite). They could have occupied the pores avoiding the release of alkali cations into the acidic solution. Regarding to sodium geopolymers, the best behavior was observed with the kaolin from Charente, which can be attributed to a more stable aluminosilicate cross-linked polymer structure formed for this material, which was corroborated with the Fourier-Transform Infrared analysis.