Durability and Carbon Emission Analysis of Mixed Sand Concrete

Using a blend of aeolian and basalt sands as fine aggregate in concrete not only mitigates the reliance on river sand in Inner Mongolia but also aligns with China’s dual-carbon strategy. This study investigates the effects of mixed sand on concrete performance and elucidates the underlying mechanisms through laboratory-based physical experiments conducted under varying environmental conditions, with concurrent analysis of its carbon emissions. The findings demonstrate that incorporating mixed sand fine aggregates reduces the interaction effects among individual aggregate particles, facilitates the formation of a more compact internal packing structure within the concrete matrix, and consequently enhances its structural density. Furthermore, the combined particle morphology and surface roughness characteristics of basalt sand optimize its bonding performance with cement paste and the interlocking effects between aggregates, resulting in a remarkable improvement in the overall strength and stability of concrete. These enhancements enable concrete to better withstand freeze–thaw expansion and crystallization pressures, thereby increasing durability under sulfate freeze–thaw, wet–dry cycles, and their combinations. The model analysis shows that the mixed sand can significantly improve the durability of concrete, especially in the sulfate-freeze–thaw and dry–wet coupling environment. Mechanism analysis reveals that the dry–wet cycle is the dominant factor in the degradation process, while an increased aeolian sand replacement rate facilitates a continuous reduction in carbon emissions. Studies have confirmed that the 1:1 compounding ratio can synergistically optimize cost effectiveness and environmental sustainability, and provide high-quality green composite fine aggregates for low-carbon concrete.