Abstract:

To achieve the efficient co-utilization of industrial solid wastes including fly ash （FA）， calcium carbide residue （CCR）， and desulfurization gypsum （DG）， 21 different mix proportion was designed to prepare ternary cementitious system. The primary objective is to elucidate the influence of material composition on workability， mechanical performance， and microstructural evolution. Furthermore， quantitative relationships between key molar ratios and strength development are established. Thermodynamic modeling is also employed to predict long-term phase stability， providing insights into the durability of the material. A total of 21 mix proportion were designed with varying mass ratios of FA， DG， and CCR at a fixed water-to-binder ratio of 0.3. The fluidity， setting time， and compressive strengths at 7 and 28 d were systematically evaluated. The phase composition and microstructure of the hydration products were characterized by X-ray diffraction （XRD）， thermogravimetric-differential thermogravimetric analysis （TG-DTG）， Fourier transform infrared spectroscopy （FTIR）， and scanning electron microscopy （SEM）. Thermodynamic simulations were performed using GEM-Selektor software with the CEMDATA 18 database to predict equilibrium phase assemblages. The results show that paste fluidity generally decreases with increasing CCR content due to the porous structure and water absorption capacity of CCR， while the setting time shortens with higher DG content， attributing to the rapid hydration of hemihydrate. Spearman correlation analysis of the key parameters sulfur-to-aluminum molar ratio （S/Al） and calcium-to-silicon molar ratio （Ca/Si） reveals that the 7 d compressive strength exhibits a strong positive correlation with S/Al， indicating that early strength is primarily governed by the formation of gypsum and ettringite networks. In contrast， the 28 d compressive strength shows a strong positive correlation with the Ca/Si， indicating that long-term performance is primarily dependent on Ca/Si. When the mass ratio of FA， DG， and CCR is 70∶5∶25， the 28 d compressive strength reaches the maximum value of 15.04 MPa. Its microstructure exhibits an interwoven network of calcium aluminosilicate hydrate （C-（A）-S-H） gel and ettringite， contributing to a dense matrix. XRD and FTIR analyses confirm that the main reaction products include gypsum， ettringite， and C-（A）-S-H gel. TG-DTG results further reveal that， for three representative mixes with different CCR content， the weight loss associated with ettringite decomposition is consistent with their corresponding strength trends. Thermodynamic simulations were conducted with a fixed FA content of 70% by mass， varying the relative proportions of DG and CCR. Additional simulations were also performed with fixed FA content of 75% and 80%. The simulations predict that under long-term equilibrium， systems with high DG content tend to form more gypsum， and ettringite may disappear when DG exceeds a critical threshold. In contrast， systems with higher CCR content favor the formation of C-（A）-S-H gels. The simulations also identify the potential formation of stratlingite and gibbsite as stable phases under long-term equilibrium. These phases are not observed in the actual specimens at 28 d， likely due to their slow formation kinetics， which are limited by the relatively short curing age. These findings provide a reference for evaluating the long-term durability and phase stability of the material.

Key words: cementitious material, industrial solid waste, synergistic stimulation, mechanical property, microstructure, thermodynamic simulation