Unilateral NMR Evaluation of Anti-Weathering Consolidation in Bricks from the Great Wall and the Altar of Agriculture (Beijing, China)

The intensification of weathering deterioration poses a serious threat to the long-term preservation of historic brick masonry; however, quantitative and in situ methods for assessing the effectiveness of consolidation treatments remain limited. In this study, unilateral nuclear magnetic resonance (NMR) and magnetic resonance imaging (NMR imaging) were employed as non-destructive techniques to evaluate the anti-weathering consolidation performance of two important historic brick materials: bricks from the Great Wall and the Altar of Agriculture (Beijing, China). Two commonly used consolidants were comparatively investigated: 1% limewater and a 10% potassium silicate-based consolidant in solution. The results showed that the 10% PS solution outperformed 1% limewater in filling large pores within the weathered layer, reducing pore size, and stabilizing the structure of the unweathered inner layer, thereby providing superior consolidation performance. These findings demonstrate that unilateral NMR and NMR imaging can serve as an efficient and non-destructive tool for quantitatively characterizing depth-dependent porosity and pore-size parameters before and after treatment, enabling reliable evaluation of consolidation effectiveness in historic brick materials and providing support for heritage conservation practice.