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

Abstract

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.