Synergistic activation of steel slag by triethanolamine (TEA) and CO₂: Hydration-carbonation coupling mechanism and performance enhancement

To overcome the dual bottlenecks of low hydration activity and poor carbonation efficiency of steel slag (SS) and achieve more efficient direct utilization, this study employs a direct gas-solid carbonation approach, adjusting the addition of triethanolamine (TEA) (1 and 3 wt%) to investigate its effect on the hydration-carbonation coupling process. The results show that under standard curing conditions, 1 wt% TEA accelerates the dissolution of brownmillerite and mayenite, promoting the formation of AFt, pyroaurite, and katoite. Although the induction period of C₂S is extended to approximately 12 h, the subsequent formation of C–S–H accelerates. During the carbonation phase, the high Ca/Si ratio C–S–H formed during early hydration becomes the primary reaction site for CO₂, inducing the precipitation of carbonates (vaterite/aragonite), which refine the pore size and reduce the total porosity to 15.75 %. Accordingly, the compressive strength after 7 days reaches 39.08 MPa (a 220 % increase compared to the control group), with a CO₂ sequestration of 7.69 g CO₂ per 100 g of SS, and a carbonation degree of 21.5 %. In contrast, 3 wt% TEA promotes the accumulation of iron-containing katoite on the surface of steel slag, which weakens the positive coupling of hydration and carbonation reactions. Although vaterite was generated after carbonation curing, the net carbonate formation still decreased. This study establishes a cement-free system for the hydration and accelerated carbonation of steel slag under normal temperature and pressure conditions, providing a sustainable strategy for CO₂ capture in low-carbon cementitious materials and resource utilization of steel slag, while offering insights for the low-carbon transformation of the cement industry.