Developing low carbon molybdenum tailing self-consolidating concrete: Workability, shrinkage, strength, and pore structure

Abstract Incorporating mineral admixtures is essential to modulate the fresh and hardened properties of self-consolidating concrete (SCC). This study introduced waste molybdenum tailings (MT) as a novel mineral admixture, substituting fly ash in SCC for the first time. The fresh, mechanical properties and drying shrinkage (DS) of SCC were assessed at various MT substitution levels (0, 25, 50, 75, and 100%). Pore structure and microstructure were analyzed using nuclear magnetic resonance and scanning electron microscopy. Increasing MT content resulted in a decline in initial flowability and a gradual increase in early-stage shrinkage. Specifically, at 100% MT replacement, the slump flow decreased by 17.5%, and the DS increased by 65.3%. Notably, the incorporation of MT significantly improved early compressive strength, primarily due to the accelerated hydration reactions. At 3 days, the 25% MT mixture showed a 33.3% increase in compressive strength compared to the control group, demonstrating MT’s positive impact on early-age strength development. At 28 days age, the 25% MT exhibited comparable strength to the control group, with compressive strength and splitting tensile strength of 38.5 and 2.67 MPa, respectively. Our findings illuminated that the strength enhancement at 25% MT was rooted in the refinement of pore structure and interface between aggregate and hydration products, evidenced by a rise in the fraction of pores with dimensions smaller than 100 nm and a marked reduction in bigger ones.