Study of thermomechanical properties of foamed and unfoamed fly ash-based geopolymer using FT Raman spectroscopy and 29Si MAS NMR

The aim of this work is to investigate the influence of exposure to high temperature on the mechanical and microstructural properties of geopolymers (GP) and geopolymer foams (GPF). The GPs were elaborated using fly ash sourced from the Jorf Lasfar power plant in Morocco with the alkaline solution. The samples prepared and cured for 28 days were exposed to high temperatures (300 °C and 600 °C). Compressive strength tests on the prepared samples were carried out before and after heat treatment. X-ray fluorescence (XRF), X-ray diffraction (XRD), FT Raman spectroscopy, Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy (29Si MAS NMR) and scanning electron microscope (SEM) analysis were performed for the characterization of the raw materials and the elaborated GP. The structures of GP and GPF, as well as the microstructural changes observed after heat treatment, were studied using FT Raman spectroscopy and 29Si MAS NMR. Raman spectroscopy results showed for GP and GPF samples that the bond assigned to Si-O-Si, Si-O-Al or O-Si-O shifted to a lower wavenumber after exposure to high temperatures.