Synergistic effects of carbonated magnesium slag and calcined coal gangue on composite cement properties

Abstract

This study investigates the synergistic effects of carbonated magnesium slag (C-MS) and calcined coal gangue (T-CG) on the properties of composite cement. Various blends of C-MS and T-CG were used to substitute 50 % of ordinary Portland cement, with ratios ranging from 0:100–100:0. A combination of multiple techniques, namely compressive strength testing, isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis-derivative thermogravimetric analysis (TG-DTG), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), and low-field nuclear magnetic resonance (NMR), was systematically employed to examine the mechanical properties, hydration kinetics, microstructure, and phase composition of the composite cements. Results demonstrated that the optimal C-MS: T-CG ratio for mechanical performance is approximately 4:1. While early-age strength was initially lower than the control group, most composite blends achieved comparable or superior strength by 60 d. Hydration kinetics revealed a synergistic effect between C-MS and T-CG, with C50 + TCG50 exhibiting the highest cumulative heat release. Microstructural analysis showed enhanced formation of needle-like AFt and C-S-H gel in the composite cements. XRD and TG-DTG analyses further confirmed the formation of carboaluminate phases (including Hc, Mc) and a lower of content Ca(OH)₂ in composite cements, especially those with a relatively higher content of T-CG. FTIR indicated the formation of more Si-rich C-S-H gel in the blended systems. This research provides valuable insights into the complex interactions between C-MS and T-CG in composite cements, which could potentially contribute to the further development and optimization of such composite cements in the field of civil engineering.