Multitechnique investigation of concrete with coal gangue

Although the research of coal gangue as construction aggregate has been conducted for many years, the fundamental knowledge about the links between the microscopic properties of coal gangue and the macroscopic properties of concrete has not been discovered yet. In this paper, gravel was entirely replaced by coal gangue to improve the utilization rate. The compressive strength, fluidity, and compactness of concrete were studied to explore the macro performance of coal gangue concrete (CGC). Meanwhile, mercury intrusion porosimeter (MIP), scanning electron microscope (SEM), and nanoindentation were used to comprehensively analyze the pore structure, morphology, and micromechanical properties of coal gangue as aggregate. The experimental results showed that coal gangue has a hierarchical structure, wide pore distribution, and poor mechanical properties in microcosmic. Compared with ordinary concrete (OC), both the fluidity and compressive strength of CGC were lower. However, due to the large porosity and water absorption of coal gangue, the bonding surface between coal gangue and cement was denser, which makes the overall compactness of CGC better than OC. The width of the interface transition zone (ITZ) of CGC did not change significantly with the water-cement ratio (w/c), while that of OC did. When w/c was greater than 0.4, the compressive strength of CGC was only about 10% lower than that of OC. The pore structure and micromechanical properties of coal gangue determined the compactness and strength of CGC.