Hyperspectral imaging-based insights into water penetration resistance of blast furnace slag-blended cementitious materials and its relation to microstructure

The durability of cementitious materials is strongly influenced by water penetration, which is closely related to pore structure and interfacial transition zone (ITZ) characteristics. However, the effects of blast furnace slag (BFS) replacement on water distribution and the associated microscale mechanisms require further investigation, especially with respect to the relation to ITZ characteristics beyond conventional porosity and thickness. This study employed near-infrared hyperspectral imaging (NIR-HSI) to visualize water distribution in BFS-blended cementitious materials, combined with pore structure analysis, Energy dispersive spectrometry (EDS), and microhardness testing to elucidate microscale mechanisms. Results show that specimens with 40% BFS replacement dosage exhibit the lowest absorption rate and sorptivity. HSI reveals that more water reaches the wetting front of specimens without BFS, generating narrow transition zones and uniform profiles, while BFS replacement broadens transition areas and produces nearly linear water content gradients in transition areas. In terms of microstructure, this study emphasizes a broader set of microstructural parameters, BFS replacement not only refines the overall pore structure and reduces thickness of ITZ, but also modifies the ITZ with fewer large pores, higher average form factor, increased fractal dimension, and lower entropy. These changes collectively generate a denser, more regular, and more tortuous pore network, which effectively restricts capillary transport and slows water penetration. EDS analysis and microhardness testing further confirm these structural improvements. These findings offer NIR-HSI-based and detailed microstructural insights and practical guidance for designing durable BFS-blended cementitious materials.