Introduction Steel slag is a solid waste produced from steelmaking, which has a potential cementitious activity. However, its cementitious activity is much lower than that of Portland cement. Mechanical grinding, acid activation, alkali activation, high-temperature curing, modification/reconstruction and organic activation methods are commonly used to improve the hydraulic activity of steel slag. Triethanolamine is commonly used as an organic admixture to improve cementitious activity of steel slag. The existing research on the hydration of TEA on steel slag still focuses on a steel slag-cement composite system, in which the proportion of cement is higher and the hydration rate is faster, so the results obtained are related to cement hydration, and it is difficult to characterize the effect of TEA on steel slag. It is thus necessary to investigate the hydration of pure steel slag in the presence of triethanolamine. In this paper, the hydration characteristics of pure steel slag under the complexation of TEA were characterized by compressive strength, heat of hydration, thermogravimetry, phase analysis, complexation ability and dissolution characteristics as well.Methods The compressive strength of hardened steel slag paste was tested. In this work, the hydration characteristics of steel slag were investigated at different TEA concentrations, and the concentrations selected were 0, 500, 1 000 mg/L and 2 000 mg/L. A mass ratio of TEA solution to steel slag was kept at 0.35. The size of test block was 20 mm×20 mm×20 mm, and the curing age was 3, 7 d and 28 d. In the process of compressive strength testing, the test entrance force was set to be 200 N, and the pressure was applied by force control, and the pressure rate was 100 N/s. After the compressive strength was tested, the specimens were smashed (<5 mm) and the center portion of the specimens was immersed in an isopropanol solution to terminate hydration, and the terminated hydrated steel slag pieces were dried in a vacuum drying oven at 40 ℃. After drying, steel slag pieces were ground and sieved through a 200 mesh (74 μm) sieve. A portion of steel slag powder was taken for thermogravimetric analysis and X-ray diffraction (XRD).The hydration heat of steel slag paste was determined using calorimetry, and the exothermic process of hydration was recorded from the addition of water or TEA solution for 72 h. The TEA solution concentration and its ratio to steel slag both were consistent with the tests of compressive strength. The complexation ability of TEA with different metal ions was determined by a conductivity method. The complexation ability of TEA with metal ions was characterized via continuously adding TEA to a solution of metal ions at the same concentration and recording the conductivity data. The conductivity method was also used to characterize the dissolution process of steel slag in the presence or absence of TEA. The conductivity of solution without steel slag was the initial value, which was measured from the contact of steel slag with water and recorded continuously for 25 min.Results and discussion The compressive strength of hardened steel slag paste with TEA is higher than that of the blank group without TEA at each age. This indicates that TEA can simultaneously increase the early and late compressive strength of hardened steel slag paste, and this strengthening effect increases with the increase of TEA concentration. When TEA is in steel slag paste, the diffraction peaks of monocarboaluminate (Mc) appear, and the diffraction peaks of C2F gradually become weaker. This indicates that TEA can promote the formation of Mc, and the content of CaCO3 is fixed at different TEA concentrations, so it can be inferred that TEA promotes the formation of Mc via promoting the hydration of aluminum phases. Meanwhile, TEA promotes the hydration of C2F, and [Fe] in C2F can participate in the formation of Mc as a substitutional ion of [Al] to form . The heat of hydration and thermogravimetric tests further indicate that TEA can promote the hydration of aluminate and ferrate phases. The hydration degree is enhanced by the formation of a large amount of Mc. The increase in hydration degree ultimately leads to an increase in compressive strength.The promotion of Mc formation by TEA is related to its complexation. When the concentration of TEA is less than or equal to 0.05 mol/L, i.e., the molar ratio of TEA to metal ions is less than or equal to 1, the complexation ability of TEA on Fe3+ is stronger than that of Al3+ and Ca2+. When the concentration of TEA is greater than or equal to 0.05 mol/L, i.e., the molar ratio of TEA to metal ions is greater than or equal to 1, the complexation ability of TEA on Al3+ is stronger than that of Fe3+ and Ca2+. TEA promotes the dissolution of mineral phase in steel slag through complexation. The free-moving metal ions and the complexed metal ions in liquid phase of steel slag can simultaneously participate in the precipitation reaction of hydration product, producing a large amount of Mc, and thus improving the early and late hydration of steel slag paste, which in turn manifests itself as an increase in the compressive strength.Conclusions The complexation ability between TEA and metal ions and effect of TEA complexation on dissolution and hydration characteristics of pure steel slag were investigated. TEA significantly increased the early and late compressive strength of hardened steel slag paste. The main reason for the increase in compressive strength of hardened steel slag paste was that TEA improved the hydration degree of steel slag paste in early and late stages. TEA promoted the hydration of aluminate phases (C3A, C12A7) and ferrate phase (C2F), and through the interaction with carbonate, a large number of were formed, and the formation of such hydration products was the main reason for the improvement of the hydration degree and the compressive strength of steel slag paste. The large formation of Mc was related to the complexation and solubilization effect of TEA. TEA could complex with Ca2+, Al3+ and Fe3+, and the complexation of TEA promoted dissolution of steel slag and formation of metal ions that could participate in the precipitation reaction, thus promoting the hydration of steel slag paste.