Carbon dioxide mineralised iron tailings powder for high-performance mortar

This study evaluates carbon dioxide (CO2) mineralised iron tailings powder (C-ITP) as a supplementary cementitious material for eco-friendly high-performance mortar (HPM). Accelerated carbonation (15% carbon dioxide, 0.5 MPa, 60°C and 70 ± 5% relative humidity for 48 h) was employed to modify raw ITP. Crucially, the treatment passivated and partially consumed reactive free oxides, particularly free calcium oxide (CaO), thereby mitigating soundness risks. Unlike raw ITP which impairs workability, C-ITP reduced the yield stress of fresh mortar, creating a ‘ball-bearing’ effect by way of surface passivation. An optimal replacement ratio of 15% C-ITP yielded a 28-day compressive strength of ∼115 MPa, comparable to the control, while higher dosages maintained high-performance standards. Microstructural characterisation (X-ray diffraction, thermogravimetry-derivative thermogravimetry and scanning electron microscopy) demonstrated that carbonation weakened calcium oxide-related reflections, produced only limited crystalline calcite and improved the particle–matrix interface, thereby enhancing durability against chloride ingress and freeze-thaw damage. While the quantitative carbon dioxide uptake was 0.175%, the primary value lies in overcoming the technical barriers of volume instability and poor rheology. By enabling 15% cement substitution, this chemo-physical modification strategy – transitioning from expansive defects to stable interlocking structures – offers a robust technical route for reducing the carbon dioxide emissions of construction materials through waste valorisation.