Hongmei Chen

This study comprehensively evaluates the mechanical properties, shrinkage behavior, and durability of concrete prepared with limestone- and granite-manufactured sands under standard-curing and steam-curing conditions. The results indicate that limestone-manufactured sand concrete consistently exhibits superior compressive strength and splitting tensile strength across all curing ages, outperforming granite-modified counterparts. The introduction of granite-manufactured sand significantly degrades these mechanical properties, with deterioration intensifying as granite content increases. Dynamic elastic modulus and damping ratio analyses reveal that limestone-based concrete maintains the highest dynamic stiffness and lowest energy dissipation under both curing regimes, suggesting fewer internal defects. In contrast, granite incorporation reduces the dynamic elastic modulus and increases the damping ratio, reflecting structural deterioration and enhanced energy loss. Drying shrinkage tests demonstrate that limestone concrete achieves the lowest shrinkage deformation throughout the testing period, even under steam-curing conditions. Conversely, granite addition markedly elevates shrinkage, particularly under steam-curing conditions, leading to compromised volumetric stability. Durability assessments highlight that manufactured sand concrete exhibits higher capillary absorption, electrical flux, and porosity, attributed to inherent material defects and the surface characteristics of manufactured sand. Granite-modified concrete further weakens interfacial shear strength between aggregates and cement paste, indicating poor interfacial bonding. Steam curing exacerbates microstructural defects, emphasizing the need to optimize curing protocols. The findings propose strategies for enhancing manufactured sand concrete performance: improving interfacial adhesion between aggregates and cement paste, rationalizing supplementary material dosages, and refining steam curing regimes. These measures offer potential pathways to develop high-performance manufactured sand concrete with balanced mechanical and durability properties.

This paper analyzes the influence of different fibers (polypropylene fibers and basalt fibers) and fiber contents (0%–0.20%) on the bonding performance between recycled coarse aggregate concrete and steel bars. The results show that the addition of recycled aggregates can reduce the fluidity of concrete, whereas the addition of fibers can further reduce the fluidity of concrete. The addition of fibers can effectively improve the mechanical properties of concrete (polypropylene fiber can increase compressive strength and splitting tensile strength by 7.80% and 6.09%, respectively, while basalt fiber can increase compressive strength and splitting tensile strength by 8.78% and 8.31%, respectively), but excessive fiber content can actually reduce the mechanical properties of concrete. The addition of fibers can enhance the bond strength between recycled concrete and steel bars and limit the relative slip between recycled concrete and steel bars, thereby improving the bond performance. The improvement effect of basalt fibers on the mechanical and bonding properties of recycled concrete is superior to that of polypropylene fibers. The correlation between the bond strength between fiber-reinforced recycled concrete and steel bars and the splitting tensile strength of recycled concrete is better, and a calculation model for the bond strength between fiber-reinforced recycled concrete and steel bars is constructed on the basis of the splitting tensile strength as the mechanical performance index. This study can provide a basis for the application of fiber-reinforced recycled concrete technology in engineering.