Investigations on mineralogical characteristics and feasibility of coal gangue as a concrete aggregate from guizhou province, China

Coal gangue (CG) is an industrial solid waste produced by coal mining and separation that is considered to have a significant effect on the soil or water environment when exposed to the air, exacerbating ecological pollution. The comprehensive utilization of CG has always been a difficult problem due to the complex mineralogical characteristics. Producing concrete aggregates with CG is an effective strategy for utilising CG resources synthetically. This work studied the mineralogical characteristics of CG discharged from a coal mine in Guizhou Province, China, and the feasibility of producing concrete coarse aggregate by using CG particles. The results indicated that some CGs were mainly composed of coal particles, whereas others were mainly composed of noncoal particles. Based on their apparent characteristics, texture, and cross-sectional characteristics, the CG samples at this sampling point could be divided into 8 categories, and the mass ratio suitable for concrete aggregate production was less than 50%. The average pore size of CG was 5.5 nm smaller than that of the industrial (IS) aggregate, but its porosity and total pore area were 2.31% and 4.5 m²/g greater than those of the IS aggregate, respectively. CG aggregate concrete achieved a compressive grade of C40 at the appropriate mix ratio, but the mechanical properties of CG aggregate concrete were lower than those of IS aggregate concrete. The compressive strength of the concrete with the addition of coarse aggregate decreased by 17.26% at 7 days (7 d) of curing and 29.16% at 28 days (28 d) of curing compared with that of the concrete with the addition of the IS coarse aggregate. In addition, roasting at 500 °C for 2 h could increase the microhardness of this CG 40.06% higher than that without roasting. The separation of raw CG was a prerequisite for the preparation of concrete aggregate with CG, and also a direction to realize the comprehensive utilization of CG resources efficiently. Moreover, the roasting modification of this CG was an effective way to improve the mechanical performance of CG particles as concrete aggregates.