Multi-Scale Study on Mechanical Properties Evolution Behavior and Synergistic Characteristics of Carbon Sequestration of TIT High-Performance Concrete Under Multiple Curing Conditions

Titanium–iron tailings (TITs) were incorporated into a high-performance cementitious matrix to investigate the curing-dependent evolution of mechanical properties, pore structure, microstructural characteristics, and CO2 mineralization behavior under standard, steam, and carbonation curing. The results indicated that curing conditions exert a critical coupling effect on hydration progression, microstructure optimization and strength development. At the same TIT replacement level, steam curing significantly improved the strength development of TIT-HPC compared with standard curing. When the TIT replacement rate was 10%, the 28-day compressive strength under steam curing reached approximately 111 MPa, whereas that under standard curing was only 100.1 MPa. XRD identified the principal hydration and carbonation-related phases, while SEM observations showed a denser microstructure in specimens containing 10% TIT. The coexisting hydration and carbonation products refined pore structure and filled micro-defects, thereby underlying the improved macroscopic mechanical performance. These hydration and carbonation products effectively filled internal pores, refined the pore structure, and enhanced the compactness and strength of the concrete matrix. In addition, the total porosity of specimens subjected to steam curing and carbonation curing decreased by 32.9% and 10%, respectively, compared with that of specimens under standard curing. The combined effects of hydration, pore refinement, and carbonation were observed in TIT-modified systems. After 28 days of carbonation curing, the highest TG-derived carbonate-related CO2 equivalent of 15.50 wt.% was observed at 20% TIT replacement. Because matched non-carbonated TG reference specimens were unavailable, this value is interpreted as a relative indicator of carbonate formation rather than baseline-corrected net CO2 uptake.