Researchers at Yulin University in northern China tested a way to turn coal gangue, fly ash, and excavated soil into low-carbon flowable backfill, also called controlled low-strength material. The optimized mix used 60 percent cement, 25 percent calcined coal gangue, and 15 percent fly ash, with excavated soil as the main bulk filler. It reached 3.62 MPa at 28 days and cut material cost by 34.6 percent and carbon emissions by 40.3 percent per cubic meter compared with a conventional cement-based mix, according to the study in Case Studies in Construction Materials. The approach works best where heavy industry is clustered. At Jinjie Industrial Park in the Shanxi-Shaanxi-Inner Mongolia energy triangle, a coal preparation plant, power plant, and cement plant sit within two kilometers, so waste heat and short transport distances make the process practical. The authors say a 100,000 cubic meter per year operation could reuse about 99,000 tonnes of excavated soil and avoid roughly 8,760 tonnes of CO2 equivalent annually. The study is lab-based with 28-day testing, so long-term durability, freeze-thaw behavior, and leaching from hardened material still need verification. Even with those limits, it shows how co-located industries can turn disposal burdens into usable construction fill.
