Pore structure characteristics of cement mortars containing recycled brick powder of different finenesses based on NMR

To reveal the influence of recycled brick powder fineness on the pore structure of cement mortar, nuclear magnetic resonance technology combined with pore fractal theory was employed to quantitatively characterize the effects of brick powder fineness on pore characteristics, pore-system complexity, and uniformity. Grey entropy relational analysis was further used to clarify the degree of association between the particle-size distribution of recycled brick powder and the pore structure of the specimens. Finally, the comprehensive economic benefits of cement-based materials incorporating recycled brick powder were quantitatively evaluated based on a life-cycle assessment framework. The results show that the particle sizes of recycled brick powder after grinding are mainly concentrated within the range of 2-70 μm. Recycled brick powder with an appropriate grinding fineness can refine the pore-size distribution of mortar and improve matrix compactness. The pore structure of mortar containing recycled brick powder exhibits distinct fractal characteristics, and the specimen prepared with brick powder ground for 20 min presents relatively low macropore and overall fractal dimensions, indicating better pore-structure uniformity. Grey entropy relational analysis demonstrates that the contents of particles in the ranges of 10-20 μm and >60 μm show the highest correlations with porosity. Therefore, the proportions of particles within these size ranges can be selectively regulated in practical production to optimize the pore structure of the matrix. The economic benefit assessment indicates that recycled brick powder ground for 20 min achieves a favorable balance among pore-structure optimization, processing cost, and cement-replacement benefits, resulting in relatively good comprehensive performance. This study identifies a relatively suitable grinding time and key particle-size control ranges for recycled brick powder, thereby providing a theoretical basis and data support for solid-waste resource utilization and the preparation and performance optimization of green cement-based materials.