Properties, structure and mechanism of high-temperature modified steel slag based on solid waste

In this study, a composite modifier (CMCDL) containing coal gasification residue, dicyandiamide waste slag, and lake sediments was used to modify steel slag at high-temperature. Five kind of raw materials was analyzed in physicochemical properties, mineral composition and microstructure, cementitious properties and soundness, and particle size analysis, the same to steel slag after high-temperature modification (SHTM). The new mineral phases were found that tricalcium aluminate (C3A), gehlenite (C2AS), magnetite (Fe3O4), spinels (MgFe2O4), quartz (SiO2), celite (C6AF2) and diopside (CMS2) formed in the SHTM when the mass fraction increase from 10% to 30% in CMCDL. The HTM with CMCDL increases the glass phase and hydrated mineral (C3A, C3S, C2S) and in raw steel slag, promoting the disassembled of RO phase, turning the phase from FeO into MgFe2O4 and Fe3O4. MgFe2O4 and Fe3O4 have similar crystal structures, and they form mixed spinels. When the content of CMCCL (coal gasification residue: dicyandiamide waste slag: lake sediments =7:9:4) is 20%, the temperature is 1250 °C, result showed that the mass fraction of f-CaO in SHTM using CMCCL decreases from 4.81% to 1.86%, with a decrease of 61.3%, the 28-day activity index of SHTM increases up to 17.6% compared with raw steel slag, reaching 86.2%. Therefore, the CMCDL-blended SHTM can be applied harmlessly in cement and concrete, enabling low-energy fine grinding of steel slag.