MetaResource

Aiming at the prominent problems of high cost of cementitious materials and low CO₂ sequestration efficiency in mine filling, this study systematically explored the influence mechanism of the mineral activator carbide slag (CS) and its composite activation with Na₂SiO₃ (sodium silicate, S₃) on the properties of low-activity electric arc furnace slag (EAFS) and granulated blast furnace slag (GBFS)-based cementitious materials. By preparing carbon-sequestering backfill materials with CS and CS-S₃ as activators, mineralization tests were conducted under controlled CO₂ curing parameters (pressure: 0.2-0.4 MPa, concentration: 20%-60%, curing duration: 1-4 h). Comprehensive characterization via X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermo-gravimetry-differential scanning calorimetry (TG-DSC), and scanning electron microscopy (SEM) was performed to elucidate the evolution of hydration products and microstructures. It was revealed from the experimental results that, for the CS single-activation system, the 3-day and 7-day uniaxial compressive strengths (UCS) of the cementitious materials decreased with an increasing EAFS replacement ratio. The UCS peaked at 6.81 MPa (3-day) and 10.96 MPa (7-day) when EAFS replacement was 20% (with 20% or 30% CS, respectively). However, excessive CS reduced strength due to insufficient GBFS participation. The CS-S₃ synergistic activation system exhibited superior early-age strength (17.66 MPa at 3-day or 22.01 MPa at 7-day), confirming the dominant role of S₃ in early hydration. Mineralization significantly enhanced the performance of the CS single-activation system: the 3-day strength increased by 1.90-2.77 times (reaching 11.60 MPa) compared to the control group (4.20 MPa), but it weakened the CS-S₃ synergistic activation system. It was identified via orthogonal analysis that CO₂ concentration (40%) was the primary factor influencing the 3-day strength of the CS single-activation system, followed by pressure (0.4 MPa) and curing duration (1 h). This validates that mineralization can be achieved under non-pure CO₂ and non-high-pressure conditions. Microstructural analyses showed that the CS single-activation system promoted the formation of C-(A)-S-H gel and CaCO₃, whereas composite systems underwent decalcification of C-(A)-S-H gels during mineralization. This study uncovers the synergistic advantages of CS under CO₂ mineralization conditions and the incompatibility between the CS-S₃ synergistic activation system and CO₂ mineralization curing, providing theoretical foundations and technical pathways for developing low-cost mine backfill materials with high CO₂ sequestration capacity.