Study on the calorific value and cementitious properties of coal gangue with 0-1 mm particle size

Research shows that thermal treatment of coal gangue particles with a size of 0–1 mm has significant technical and economic value. Coal gangue samples from four regions were crushed and screened to compare the calorific value of 0–1 mm and 1–16 mm. The characteristics of the coal gangue before and after calcination treatment were analyzed. 0–1 mm coal gangue was used to replace 30% of cement for the preparation of paste, and macro-mechanical properties and micro-experimental analysis including XRD, TG-DTG, FTIR, and SEM were conducted. The results indicate that compared to 1–16 mm coal gangue, the calorific value of 0–1 mm coal gangue significantly increased. After calcination, the larger particles of 0–1 mm coal gangue became smaller and there was an increase in smaller particles, the XRD diffraction peak of kaolinite disappeared. Under water-cement ratios of 0.4 and 0.7, the compressive strength of cement mortar with calcined coal gangue was significantly higher than that without calcination at 28 days. The thermally stimulated coal gangue in the paste underwent a pozzolanic effect, consuming a large amount of Ca(OH)2 and forming C-S-H gel and ettringite (AFt), making the structure of the paste more dense. Under low water-cement ratios, carbon in the non-calcined coal gangue inhibited the formation of AFt during cement hydration. The higher amount of kaolinite and carbon in coal gangue, the more noticeable improvement in the performance of cement paste after calcination will be observed. Thermal stimulation treatment and heat recovery of 0–1 mm coal gangue are beneficial for using fully graded coal gangue as aggregate in cement concrete.