The effects of adding molybdenum tailings as cementitious paste replacement on the fluidity, mechanical properties and micro-structure of concrete

To reduce the land occupation and environmental pollution caused by the accumulation of molybdenum tailings (MT), MT has been used as cement or fine aggregate replacement to produce concrete. Molybdenum tailings concrete (MTC) was prepared by replacing cement paste with MT of equal mass in this study in order to offer one more option for the adding of MT into concrete. The workability of the concrete mixture and the mechanical properties of the hardened concrete were investigated. The internal pore structure characteristics and micro-morphology of MTC were analyzed by nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), respectively. The results showed that, as the MT replacement rate increases, the slump of the concrete mixture decreases, the air content increases firstly and then decreases, the compressive strength and splitting tensile strength decreases firstly and then increase with the optimum MT replacement rate at 10%; the total porosity of concrete increases and then decreases, both the compressive strength and splitting tensile strength are inversely proportional to the porosity. When the MT replacement rate is 7.5% and 10%, the number of medium capillary pores (0–100 nm) decreases significantly, while the number of capillary pores (100–1000 nm) and air pores (>1000 nm) gradually increases. • Molybdenum tailings are added into concrete as replacements of cement paste. • Nuclear magnetic resonance is adopted to analyze the pore structure. • Molybdenum tailings decreases the slump of fresh concrete. • Concrete with 10% molybdenum tailings replacement shows the highest splitting tensile strength.