Influence of physicochemical properties and shape characteristics of coal gangue coarse aggregate on concrete strength

Natural aggregate is increasingly scarce, and the reuse of solid waste is highly valued. Application of coal gangue aggregate has been drawing broad attention. However, the performance of coal gangue varies greatly in different regions, and physicochemical properties and shape characteristics of coal gangue coarse aggregate significantly affect the performance of concrete. This paper aims at the coal gangue in different mining areas of Shaanxi Province, The crushing index, water absorption, soundness, apparent density and clay content are taken as the macro indexes of coal gangue coarse aggregate, the mineral composition, chemical composition, microstructure and internal pore structure are taken as the microscopic indexes of coal gangue coarse aggregate, and analyses the association between them. In view of the shape difference between coal gangue and nature gravel, the sphericity, angular number(AN) and aggregate particle shape and texture(IAPST) are proposed as shape statistical indexes of coal gangue coarse aggregate, in order to quantify its shape characteristics. Moreover, The influence of macro indexes and shape statistical indexes of coal gangue on workability and strength of concrete are analyzed. The results show that coal gangue with high content of quartz, kaolinite and illite, dense microstructure and small porosity has low water absorption and crushing index. Compared with natural gravel, the coal gangue coarse aggregate has lower sphericity and more irregular shapes. Most coal gangues have high AN and IAPST, showing more sharp edges and rougher surface. Coal gangue with low water absorption and low crushing index is used as coarse aggregate, and the prepared concrete has good workability and high strength, which can meet the C30 strength grade. Shape statistical indexes of coal gangue coarse aggregate affects the strength of concrete when the crushing indexes of coal gangue coarse aggregate is roughly the same. The higher the sphericity, the smaller angular number and texture index, resulting in the lower concrete strength, which is due to the poor interfacial bonding between coal gangue coarse aggregate and cement.