Research on the Sustainability of Desert Sand-Recycled Concrete Based on the NMR Porosity Structure and Grey...

To investigate the mechanism by which a combination of desert sand (DS) and recycled coarse aggregate (RA) affects the sustainability of recycled concrete, multiple mix proportions with varying replacement ratios were designed in this study. Macroscopic performance tests and microscopic analyses were performed using nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and X-ray diffraction (XRD), and the results were combined with grey relational analysis to reveal the intrinsic relationships between pore parameters and macroscopic properties. Additionally, technical and economic evaluations were conducted. The results indicate that incorporating either type of aggregate individually has a nonlinear effect on the compressive strength and impermeability of concrete. The optimal compressive strength is achieved when both aggregates are used at 20% replacement, whereas the best impermeability occurs at 10% replacement for each. The proportions of transitional pores and capillary pores, along with T₂ relaxation parameters, serve as key microstructural indicators for controlling performance. Economically, the use of both aggregates together significantly reduces material costs-reaching a cost savings rate of 3.51% with a recycled aggregate replacement level of 30%. Further substitution of 30% desert sand for river sand under the same replacement ratio can reduce costs by an additional 1.56%. This mix proportion achieves optimal synergy among mechanical performance, cost control, and low-carbon benefits. The findings provide theoretical guidance and practical support for mix design, durability enhancement, and the promotion of such green, low-cost concrete in engineering applications.