Properties and hydration products analysis of magnesium slag-based filling materials

This study investigates the properties and hydration products of filling materials based on modified magnesium slag (MMS) and unmodified magnesium slag (UMS). Two types of MMS (MMS-A and MMS-B) were compared with UMS through various analyses. X-ray diffraction revealed that MMS predominantly contained β-C₂S, while UMS was dominated by γ-C₂S. Strength activity index tests showed superior performance of MMS, with MMS-A and MMS-B achieving 97.53 % and 89.46 % at 3 days, respectively, compared to 68.5 % for UMS. Isothermal calorimetry demonstrated that MMS-based pastes had shorter induction periods and higher heat release rates, with MMS-A reaching a peak of 0.470 mW/g at 30 hours, while UMS peaked at 0.203 mW/g at 66 hours. Compressive strength tests at 28 days yielded 8.39 MPa for MMS-A, 8.08 MPa for MMS-B, and 4.99 MPa for UMS-based pastes. Microstructural analyses, including SEM, TG-DTG, and FT-IR, confirmed denser C-S-H formation and more refined pore structures in MMS-based pastes. The minimal differences between MMS-A and MMS-B across all tests demonstrated the stability of the modification process. These findings suggest that MMS offers a promising alternative for sustainable filling materials in mining applications, effectively valorizing an industrial by-product while potentially improving backfill performance.