Utilization of molybdenum tailings as fine aggregate in recycled aggregate concrete

The increasing emissions of construction waste and industrial by-products have caused a serious burden on the environment. The shortage of natural coarse aggregate (NCA) and river sand provides the impetus for the reuse of solid waste. This research provides a cleaner option for the production of recycled aggregate concrete (RAC) from industrial by-product molybdenum tailings (MTs). MTs are used as alternative material to river sand (10%, 30%, 50%, 70% and 100%). Three types of concrete natural aggregate concrete (NAC), RAC, and MTs recycled aggregate concrete (MTs-RAC) were prepared. Firstly, the mechanical properties of the specimens were tested, including compressive strength (fcu) and splitting tensile strength (fst), and the digital image correlation (DIC) system was used to evaluate the strain field distribution. Then, the freeze-thaw (F-T) cycle corrosion resistance of concrete was evaluated. Subsequently, the pore structure was visualized and quantitatively analyzed based on industrial CT technology. The evolution of corrosion resistance of MTs-RAC was confirmed by microstructure. Finally, the economic efficiency factor (EEF) and environmental impact (EI) were evaluated. The experimental results showed that the appropriate amount of MTs significantly improved the pore structure and mechanical properties of RAC, and the fcu of RAC with a 50% MTs replacement rate increased by a maximum of 14.4%, which could achieve the same mechanical properties as NAC. However, the combination of excess MTs and recycled coarse aggregate (RCA) increases the porosity of concrete. The F-T cycle resistance of RAC decreased with the increase of MTs replacement rate. The increase in the proportion of large pores (>10 mm3) is the main factor leading to the destruction of F-T cycles. On balance, the replacement rate of MTs for use in RAC should not exceed 50% in salt lakes and cold regions. The results are helpful to understand the influence mechanism of MTs on RAC performance and provide the theoretical basis for the application of MTs in RAC.