Effect of Granulometry of Sawing Sludges Entrapped in Metakaolin-Based Geopolymers

The stone industry generates a large amount of sawing sludge (SS). Geopolymers (GPs) offer a circular pathway by incorporating SS into their aluminosilicate networks, helping to mitigate the environmental impact on the construction industry. This preliminary study addresses the feasibility of using four types of SS (SS1–SS4) in metakaolin-based GP formulation, evaluating the effect of two granulometries (75 μm < x < 125 μm and 125 μm < x < 300 μm) on GP properties. Geopolymerization is confirmed through Fouriertransform infrared (FT-IR) spectroscopy, while integrity and boiling water tests confirm that all samples maintained their integrity under the selected preliminary experimental conditions. Microstructural and mineralogical characteristics, investigated by scanning electron microscopy (SEM) and wide-angle X-ray diffraction (WAXD), respectively, reveal heterogeneous microstructures characterized by the presence of unreacted crystalline particles. Thermal behavior, examined through thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG), reveals total mass losses of approximately 15–18% up to 1000 °C, with an additional loss in the 500–800 °C range associated with carbonate decomposition, which is particularly evident in SS2, GP2/1, and GP2/2. Mechanical properties, through compressive strength tests, reveal higher values for GP2/1 (24.1 ± 0.4 MPa) and GP4/2 (24.7 ± 1.7 MPa) than for the GP0 control (22.5 ± 0.2 MPa). These preliminary findings support further investigations concerning the use of sawing sludges as fillers in sustainable alkali-activated materials.