Potential of copper tailings as supplementary siliceous materials in the preparation of autoclaved aerated concrete

The storage of copper tailings (CT) not only consumes considerable land resources but also tends to cause a series of ecological and environmental issues. To achieve the circular economy and green industry development, CT is utilized as a supplementary siliceous material of autoclaved aerated concrete (AAC) in this study. The effects of substitution rate of CT for quartz sand are evaluated though the flow and gas-foaming properties of fresh slurry, and the physical and mechanical properties of AAC products. Meanwhile, the relationship between the macroscopic properties and hydration products is analyzed by multiple microscopic tests, including the Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The experimental results shows that the bulk density, compressive strength and thermal conductivity of AAC incorporating CT show a trend of first decreasing and then increasing as the substitution rate of CT for quartz sand increases from 0 to 50 wt%, while the specific strength continues to decrease. When the substitution rate of CT for quartz sand is less than 40 wt%, the performances of AAC can meet the specifications of B05 A2.5 level according to Chinese national standards. These findings are closely related to the characteristics of air pore structure and the ordering, quantity and morphology of hydration products. With increasing the substitution rate of CT for quartz sand, the ordering of tobermorite gradually decreases, and its morphology transforms from plate-like to grass-like and then to needle-like, which can reduce the mechanical properties of AAC.