Study on the Mechanical Properties and Pore Structure Evolution Characteristics of Molybdenum Tailings Concrete Under Carbonization

To investigate the feasibility of using molybdenum tailings (MTs) as fine aggregate in concrete production and the impact of carbonation on the performance of molybdenum tailings concrete (MTC), this study employed mechanical property testing, strain field analysis based on digital image correlation (DIC), industrial CT, and scanning electron microscopy (SEM) to systematically analyze the evolution of carbonation depth, compressive strength (fcu), splitting tensile strength (fsts), strain field distribution, pore structure, and microstructure of MTC at different carbonation ages. The relationship between porosity and fcu and the two-parameter strength model of porosity and average pore volume were established. The results show that the carbonation depth gradually increases with the increase in carbonation age and also increases with an increase in the substitution rate of MTs. The carbonation depth of MTs completely replaced is up to 13.72 mm after 56 days of carbonation. Carbonation significantly improves the fcu of concrete, but as the carbonation age increases, the rate of strength growth generally slows down. The 2D slice visualization of the pore structure shows that the pores of the concrete are gradually filled by carbonation products from outside to inside, the edge macropores gradually disappear, and the proportion of mesopores gradually increases. The total porosity is reduced (up to 37.3%). Microscopic observations confirmed that the carbonation-generated CaCO3 filled the concrete pores and optimized the structure of the interfacial transition zone (ITZ), but the DIC strain field distribution showed that the filled part increased the brittleness of the concrete. Therefore, it is inferred that excessive carbonization may cause microcrack propagation (which will be discussed in subsequent carbonization time extension studies). The study revealed the dual effects of carbonation on the mechanical properties and pore structure of MTC, providing an experimental basis for the application of tailings in the laboratory.