Thermal behaviour of metakaolin–bauxite blends geopolymer: microstructure and mechanical properties

This paper investigates the use of bauxite widely available in northern Cameroon as an additive in the optimization of some properties of metakaolin-based geopolymer. To do this, several geopolymer mixtures were prepared by substituting metakaolin (MK) by bauxite (BA) (from 0 to 50%) and partially kept at room temperature (28 °C), while others were sintered at 200, 800 and 1200 °C. The raw materials and resulting products were characterized using X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), densification parameters, mechanical properties as well as microstructural morphologies. The results revealed that the setting time of the geopolymer pastes increased with the bauxite content due to its low dissolution in alkaline medium at room temperature. The mechanical strength of samples decreased from 35.20 to 11.10 MPa at room temperature. At 1200 °C, the higher strengths (50, 98 and 70 MPa) were achieved in MKBA10, MKBA20 and MKBA30, respectively. These samples also exhibited dense and compact microstructure partially due to packing particles effect and the nature of bauxite known as refractory material. Thermal shrinkage and relatively high mass losses reflected the decomposition of chemical compounds within the system. Thus, the synthesized materials heated at 1200 °C could be used as a potential candidate for refractory applications.