Kill two birds with one stone: Contribution of steel slag on enhancing the performance of coal gangue-based cementitious materials and simultaneous sulfur fixation

The thermal activation of coal gangue (CG) is essential for its application in cement system; however, controlling the sulfur emission and improving the hydration activity to CG during activation are considerably challenging. Steel slag (SS), a potential additive, can simultaneously enhance cementitious material strength while attaining sulfur fixation. This research tries to introduce SS to solve CG dual puzzle and reached "kill two birds with one stone". The results indicate that the calcination behavior of CG can be divided into three stages, with most calcination occurring in the second stage and calcination inhibited during the main weight loss stage. CG primarily releases sulfur in the form of SO2 and H2S during the combustion. Sample G2S1(CG:SS = 2:1) showed the highest sulfur fixation efficiency, with 67.87% for total sulfur gas, 94.73% for H2S and 66.91% for SO2. SS reduced the required average activation energy by nearly half, indicating that SS has a significant impact on lowering the energy barrier and enhancing the overall activity. Together with sulfur fixation, G2S1 calcined at 600 degrees C considerably improved the performance of cementitious materials, with the compressive strength reaching 82.67 MPa. The mechanism of achieving the "kill two birds with one stone" objective can be attributed to the introduction of SS, which provides an abundant supply of calcium. On the one hand, it facilitates the sulfur fixation process by forming CaSO4. On the other hand, it contributes to the availability of CaO in the cementitious material, accelerating the formation of C-S-H gel.