Influence of molybdenum tailings replacing river sand on mechanical properties and concrete microstructure

Many tailings are piled up, occupying land and polluting the environment. Tailings replace river sand to prepare concrete. It can reduce the tailings stockpile and slow the consumption of non-renewable resources. This study discussed the feasibility of molybdenum tailings (MTs) replacing river sand in preparing concrete. Firstly, the influence of the MTs addition amount on concrete strength was analyzed. Secondly, nuclear magnetic resonance (NMR), x-ray diffraction (XRD), thermogravimetric (TG-DTG), and scanning electron microscope (SEM) were used to characterize the microscopic characteristics of concrete with different MTs contents. The results showed that good gradation of fine aggregate could improve the strength of concrete. The optimum replacement rate of MTs was 20 %, and the 28-day compressive strength and tensile strength of concrete increased by 10.9 % and 14.9 %, respectively, compared with the control group. It cannot be considered that the greater the total porosity, the greater the strength of concrete, which was mainly determined by the proportion of pores with different pore sizes in the total pores. When the amount of MTs added was 20 %, the MTs played a role in dilution, promoting cement hydration. The hydration products can not only effectively fill the internal pores of the concrete but also improve the bond strength between the tailings and the hardened slurry, thus improving the strength of the concrete. When the content of tailings added was 50 % and 100 %, cement hydration was blocked, increasing concrete porosity, and the interfacial transition zone (ITZ) became looser, thus weakening the strength of concrete.