Mechanical Properties and Mineral Characteristics of Multi-Source Coal-Based Solid Waste Filling Materials under Different Proportioning

Traditional grouting materials have certain limitations, such as greater cement consumption, high cost, slow setting rate, and insufficient early strength, hindering their wide applicability. In this paper, desulfurization gypsum (DG) and fly ash (FA) are used as the main raw materials, supplemented by a small amount of Portland cement (PC), to develop a low-cost, fast-setting, and high-early-strength filling material. The mechanical properties and setting characteristics were assessed for varying PC, DG, and FA ratios. The effects of different mineral crystal formations on mechanical properties and hydration characteristics were analyzed. The results show that adding DG leads to a sudden decrease in mechanical properties while accelerating the setting. The compressive strength and setting rate increase with increasing DG content. FA can assist in PC hydration and delay the setting time, and the dosage should be limited to 20%. A synergistic enhancement effect between DG and FA can be achieved, forming grossular-type aluminosilicate and promoting compressive strength development. The optimal performance is achieved when PC, DG, and FA are added at 20%, 60%, and 20% dosages, respectively.