The role of silica fume in activating composite cementitious materials blended with red mud and phosphogypsum
Yong Li, Mingxuan Shen, Yu Tao Zhao, Wei Tang, Xiaohu Chen
Abstract
Using red mud (RM) and phosphogypsum (PG) as supplementary cementitious materials (SCMs) enabled large-scale industrial waste treatment and optimized resource utilization in cement production. Nonetheless, the mechanical strength of composite mortar and workability of composites manufactured by these materials were not optimal. This study introduced silica fume (SF) as a crucial activator to enhance hydration in RM-PG-OPC systems. Both the strength and workability of RM-PG-OPC cementitious system were improved by incorporating SF. Results indicated that the optimal component-mix ratio of RM, PG, and SF with replacing 30 % OPC, was 15:8:7. The compressive strengths of composite mortar were 27.30 MPa and 41.30 MPa, accounting for 103.40 % and 105.36 % of OPC (26.40Mpa and 39.20Mpa) at 3 and 28 days, respectively, with initial and final setting times of 290 min and 370 min. It was also revealed that the RM-PG-SF-OPC cementitious system exhibited the highest cumulative exothermic rate at 72 h, attributed to SF’s nucleation and pozzolanic effects. Based on the analysis of X-ray diffraction (XRD), thermogravimetric analyzer (TG), and scanning electron microscope-energy dispersive spectrometer (SEM-EDS), It was further demonstrated that SF involved in the RM-PG-SF-OPC cementitious system not only enhanced the leaching levels of Ca 2 + , Mg 2+ , and Al 3+ , but also facilitated reticular nucleation on SF particles, which promoted the formation of C-(A)-S-H, ettringite (AFt), and a denser gel structure. This research aims to optimize the RM-PG-OPC cementitious system by adding SF and provide guidance for large-scale treatment and efficient resource utilization of industrial solid wastes.