Use of ladle furnace slag as supplementary cementitious material before and after modification by rapid air cooling: A comparative study of influence on the properties of blended cement paste

Ladle furnace slag (LFS) exhibits excellent early hydration activity due to its special mineral component C(12)A(7). The mineral phase of LFS was optimized and modified by rapid air cooling, which could effectively improve the volume stability and the content of active substances in the amorphous phase of the LFS. To study the performance advantages of LFS after modification by rapid air cooling (CLFS), the hydration processes, physical and mechanical properties, and volume stability of the LFS-OPC (ordinary Portland cement) system before and after modification were compared and analyzed from a macroscopic perspective. The microstructures, compositions, and pore structures of the CLFS-OPC hardened pastes at different ages were studied. The results showed that both CLFS and LFS can accelerate the hydration and setting of cement significantly. With the increase in the LFS content, the second hydration exothermic peak of cement gradually became divided into two main exothermic peaks, which were mainly due to aluminate hydration and silicate hydration. Compared with the LFS-OPC, the CLFS-OPC exhibited a faster hydration rate and shorter setting time. In addition, the mechanical properties and volume stability of the CLFS-OPC were better than those of the original system due to the existence of more active beta-C2S crystal forms and smaller f-MgO particles in the CLFS, which provides a good foundation for the use of CLFS to promote the setting of cement-based cementitious materials. CLFS is recommended to be used as mineral component regulator with a dosage of 5% similar to 10%.