Rapid visualization and quantification of water penetration into cement paste using near-infrared hyperspectral imaging

Water penetration is the leading cause of durability deterioration of cementitious materials, and the rapid in-situ visualization and quantification of water penetration process is important for evaluating water absorption behavior and durability of material. This study proposed a novel method to rapidly visualize and quantify the water penetration into cementitious materials using near-infrared hyperspectral imaging. Specifically, three different areas were distinguished as the dry area, the transition area (including wetting front) and completely wet area during the water absorption process based on the reflectance gradient of cement paste. A strong linear relationship between reflectance and water content was established through slice weighing calibration, enabling accurate quantification of water absorption. The real-time tracking of the water content distribution and penetration depth evolution was realized. Furthermore, the study revealed that water absorption behavior is significantly governed by local pore structure, and momentum balance of capillary water absorption behavior in porous media was used to explain the dynamic water transport mechanisms. Compared to traditional visualization techniques, the proposed method has achieved a millisecond-level breakthrough in time. This study provides an efficient and practical reference for on-site in-situ quantitative evaluation of cementitious engineering structures.