Synergistic enhancement of converter steelmaking slag, blast furnace slag, Bayer red mud in cementitious materials: Strength, phase composition, and microstructure

Abstract

The dosage of converter steelmaking slag (CSS) is less than 20 wt% in the field of cementitious materials. This work aims to increase the dosage of CSS in cementitious materials containing multiple types of solid wastes. It is found that the dosage of CSS in the cementitious material is 30 wt% in this work, which is beneficial to promote the synergy of CSS, Bayer red mud (BRM), and blast furnace slag (BFS). In this research, the strength of P·Ⅰ 42.5 cement is raised to the P·C 52.5 cement level due to the synergy of CSS, BRM, and BFS. The compressive strength values in CSS-based cementitious material No. 5 (CSSM5) at 3 days (22.90 MPa) and 28 days (56.30 MPa) are highest when the (CaO+Na2O)/(SiO2+Al2O3) mass ratio is 1.64, which meet strength standard of P·C 52.5 cement. The major phase composition is C–S–H gels, ettringite, and N, C-A-S-H gels that facilitate the improvement of compressive strength. The density of microstructure and pore structure of CSSM are optimal, with a (CaO+Na2O)/(SiO2+Al2O3) mass ratio of 1.64. In addition, the thermogravimetric mass loss of ettringite and C–S–H gels in CSSM5 is the maximum (7.79 wt%), which is beneficial to the development of strength. The results of this work have potential as a valuable reference to the synergy of CSS, BFS, and BRM in cementitious materials, and also highlight the potential to utilize solid waste as a secondary material in the production of useful resources.