Comparative study of geopolymers synthesized with alkaline and acid reactants at various liquid-to-solid ratios using Moroccan kaolin clay

Abstract

This study explores the underutilized potential of Guenfouda kaolin as a raw material for geopolymer synthesis, addressing the gap in comparative analyses of acidic and alkaline activation methods. Geopolymers were synthesized using thermally activated natural kaolin (metakaolin) with sodium-based alkaline (NaOH and Na₂SiO₃) and phosphoric acid (H₃PO₄) activation methods, with a focus on the effect of varying Liquid-to-Solid (L/S) ratios (0.5, 0.6, 0.7, and 0.8). Raw materials and geopolymers were characterized by X-ray fluorescence (XRF), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), compressive strength testing, and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS). Characterization of the kaolin revealed its rich alumina and silica content, making it an ideal precursor for geopolymer synthesis. XRD analysis showed a broad amorphous bump without significant variation in the crystalline structure of geopolymers at different L/S ratios. FTIR spectroscopy findings revealed the presence of specific bands related to aluminosilicate networks in alkaline geopolymers and characteristic bonds associated with phosphosilicate networks in acid geopolymers. The mechanical performance results showed that the compressive strength of alkaline geopolymers reached a maximum of 28.25 MPa at an L/S ratio of 0.6, while that of acid geopolymers was 22.73 MPa at an L/S ratio of 0.8. Densification of the geopolymer structure is improved by increasing the L/S ratio, according to SEM images. This is particularly observed at optimal ratios, where homogeneous microstructures were noted in both types of geopolymer. This study advances the sustainable utilization of local kaolin, offering novel insights into optimizing geopolymerization processes for eco-friendly construction materials.