The impact of microwave curing on the strength and microstructure of coal gangue concrete

The disposal of coal gangue through landfilling leads to resource wastage and environmental hazards. Coal gangue in Wuhai City, Inner Mongolia, is characterized by high carbon content, abundant kaolin components, liquefaction upon contact with water, and a layered structure. Utilizing it as coarse aggregate in concrete results in relatively low early strength. This study investigates the effects of microwave curing power and curing duration on coal gangue concrete (CGC) using microwave curing technology. The compressive strength and split tensile strength of CGC were tested, and the failure modes under microwave curing were analyzed. Optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) were employed to characterize the phase composition, microstructure, and pore structure of hydration products under different microwave curing regimes. Results indicate that compared to standard curing, at microwave powers of 120 W and 260 W, within 3-5 cycles, the compressive strength and split tensile strength of CGC at 1 day can be improved by up to 98 % and 33 %, respectively. With prolonged curing duration, strength initially increases and then decreases, with improved integrity of the concrete after failure. Microwave curing increases the formation of C-S-H gel in the hardened paste. It also leads to denser spatial binding and reduces the interface width between the paste and coal gangue aggregate. The concrete porosity decreases from 7.11 % to 1.66 % at 1 day. Therefore, microwave curing technology enhances the early strength of CGC. Applying this technology in producing prefabricated concrete slope protection structures in coal gangue landfills allows for large-scale in-situ utilization of coal gangue.